One of the most important features offish culture is that the fish should have good food. Feeding and fertilization together make the pond culture successful. The growth offish in the ponds is directly related to the amount of food available in the pond. The pond must provide all the food and nutrients that the fish need. But all fishes do not need the same kind of food, for different species feed on different types of food, fish also feed on different foods depending on the stage of their life cycle.
Newly hatched hatchlings absorb feed from their yolk sac until the yolk in the yolk sacs is exhausted. The fry eat the smallest phytoplankton in the pond. Adult fish feed on a particular kind of food that fish enjoy plankton, aquatic weeds, worms, insect larvae, etc.
As the aquaculture technology evolved, there has been a trend towards high yields and faster growth of fish. It is necessary to enhance the food supply by fertilization, supplementing the food with artificial feed or providing all the nutrients to the fish in a cultivating field. As the fish becomes less dependent on natural food organisms and more dependent on artificial food, the need for nutritional artificial feed becomes necessary.
With the advancement offish culture technology, the extensive carp farming method has gradually shifted towards intensive culture method. The fish originally lived solely on the natural products of the pond for growth, reproduction and health. In the farming habitat, feeding of stocked population with nutritionally balanced and quality test diet is of critical importance to ensure optimal biological and physiological processes as well as production. However, test diets are either dried, semi-dried, moist, encapsulated or particulate diets. Dried diets includes the diets of pure plant origin, animal tissue meal, compounded or formulated meals.
Compounded diets should contain adequate level of nutrients to meet the physiological requirements of the organisms such as energy, body building, repair or maintaining cells, tissues and regulating body processes. According to Halver (1976), any nutritionally balanced compounded diet must include an energy source with sufficient essential amino acids, essential fatty acids and non-energy nutrients to maintain and promote growth. Any imbalance in these nutrients may show sparing action that would affect the efficacy of conversion of food by the organisms. The specific nutritional requirements offish vary greatly with species, size, physiological condition, temperature, stress, nutrient balance of the diet and environmental factors. Therefore, programming of nutrient constituents must be done in order to have most economic compounded ration for fish.
The knowledge relating to basic nutritional requirements of fishes stems from man’s endeavers to raise fishes for food and for stocking in lakes and rivers. In intensive fish culture practices the objective is to maintain optimum density of fish per unit area of water by adopting techniques relating to polyculture, multiple stocking, stock manipulation etc. Under such conditions of fish culture, the natural protein component of food organisms present in the environment will not meet the needs of the growing fish biomass, thereby necesciating supplementation with protein rich feeds. Since there is heavy competition of protein foods mainly for human consumption the idea of feeding such type of foods to all cultivated species. Of fishes does not sound very economic. There are certain foods which are not consumed by the human beings such as plant proteins, condemned grains straw, hay, scrap or human food, by products and wastes from industries, single cell proteins etc. To achieve progressive development of the fish farming industry such substances could be utilized for the preparation of artificial fish feeds after conducting proper experiments.
The development of artificial feeds mainly depend on the studies relating to basic nutrition and physiology. For economic reasons such investigations should aim to find out the minimum level of protein which satisfies the amino acid requirements of the species for optimum inherent capacity for growth, adequate supplementation by carbohydrates to serve as dietary calories and luxurious supply of vitamins and minerals for necessary stimulation of protein digestion.
Information regarding the nutritional requirements of warm water fishes is not available excepting the channel cat fish for which complete ration has been formulated and dietic requirements have been studied. However, the importance of giving protein rich diets to carps has been realized in view of the high yields obtained. It has been established that the natural food plays only and insignificant role. Results obtained by feeding carps in running and confined water practices, in cages and floats have revealed that carp can grow well even without natural food by feeding with different types of supplementary feeds.
Natural fish food organism
A variety of natural fish food organisms are found in a waterbody, which depend on the nutritive nature of the waterbody. The natural food provides the constituents of a complete and balanced diet. The demand of natural food varies from species to species and age group of individuals. For example catla prefers zooplankton and silver carp prefers phytoplankton. At a younger stage; the fish may feed on plankton, and the same fish may prefer animal food as an adult Fishes feed on different natural food organisms at all the different trophic levels. Natural feeds have high protein and fat contents, which promote the growth of the fish. Hence, it is necessary to increase the live food in the aquatic ecosystem to improve the growth of the fish.
Classification of food and feeding habits of fishes
Different authors have classified natural food and feeding habits of the fishes (Schaprclas, 1933).
1. Main food : It is the most preferred food on which the fish will thrive best
2. Occasional food : It has relatively high nutritive values and is liked and consumed by fish whenever the opportunity presents itself.
3. Eniergency food: It is fed upon/ accepted when other food material is not available.
Nikolsky (1963) recognised 4 main categories of food on the basis of their importance in the diets of fishes.
Basic food: It is normally eaten by the fish and comprises most of the gut contents.
1. Secondary food : It is frequently consumed in smaller quantities.
2. Incidental food : It is consumed rarely.
3. Obligatory food : The fish consumes this food in the absence of basic food.
Based on the nature of food, Das and Moitra (1963) classified the fishes into 3 primary groups. x
1. Herbivorous fishes : They feed on plant material, which forms more than 75% of gut contents.
2. Omnivorous fishes : They consume both plant and animal food.
3. Carnivorous fishes : They feed on animal food, which comprises of more than 80% of the diet.
Herbivores are divided into 2 sub-groups.
a. Planktophagous fishes : They consume only phyto- and zooplankton
b. Detritophagous fishes : They feed on detritus.
Omnivores can also be grouped into 2 categories.
a. Herbi-omnivores : Fishes feed more on plant material than animal food,
b. Cami-omnivores : Fishes feed more on animal food than plant material.
Carnivores are also classified into insectivores (feed on insects), carcinophagous (feed on crustaceans), malacophagous (feed on molluscans), piscivorous (feed on other fishes), and larvivorous (feed on larvae). Some fishes are cannibalistic.
The fishes consume a variety of food material, such as phytoplankton, zooplankton, aquatic weeds, animals like annelids, arthropods, molluscs, other fishes and amphibians.
Plankton
Fish production in a waterbody is directly or indirectly dependant on the abundance of plankton. The physico-chemical properties of water determines the quality and quantity of plankton. Thus, during the study of plankton, a link in the food chain is a pre-requisite to understand the capacity of the waterbody to support the fisheries and the need for introduction of additional selected species of commercially important fishes. Other two categories of life in an ecosystem are benthos and neckton. Benthos is the term given to life at the bottom, like aquatic earthworms, insect larvae and certain fishes. Neckton includes the larger swimming animals like fishes. Plankton is most essential for many fishes as food. The growth of plankton feeding fishes mostly depends on plankton dynamics of the waterbody. The plankton is further divided into two main categories – phytoplankton and zooplankton.
Phytoplankton :
Fishes consume the phytoplankton, which is found abundantly in well managed ponds. Phytoplankton gives green colour to the water due to the presence of chlorophyll. Phytoplankton are generally made up of mostly unicellular algae which are either solitary or colonial. Phytoplankton are autotrophs, i.e., they fix solar energy by photosynthesis using CO2, nutrients and water. Phytoplankton occupy the base of the food chain and produce the food material on which other organisms in the ecosystem sustain themselves. The phytoplankton drift about at the mercy of the wind and water movements. Algae consist of three major classes which form the main food in phytoplankton (Fig. 6.1) . These are chlorophyceae, cyanophyceae and bacillariophyceae.
a. Chlorophyceae:
These are called green algae due to the presence of chlorophyll. Many chlorophyceae members are useful as food to fishes. These organisms are distributed all over the pond. The chlorophyceae members useful as fish food are Chlamydomonas. Volvox, Eudorina, Pandorina, Chlorella. filamentous algae like Ulothrix, Oedogonium, Spirogyra, Pediastrum, Microspora, Cladophora, Clostredium, Scenedesmus, Cosmarium. etc.
b. Cyanophyceae: These are also called as myxophyceae and are commonly known as blue green algae. This colour is due to the varying proportions of chlorophyll a. carotenoids and biliproteins. The product of photosynthesis is cyanophycean starch, present in granular form. The cell wall lacks cellulose and instead comprises mainly of aminoacids and amino sugars. Many cyanophycean members are consumed by fishes. These are Nostoc, Oscillotoria, Anabaena, Microcystis, Spirulma. Merismopedia, Arthrospira, etc. 1.2.1.3. Bacillariophyceae .-These are called diatoms. They are unicellular organisms with different shapes and sizes. These may be yellow or golden brown or olive green in colour. Golden brawn diatomin pigment is present in diatoms. The reserve food materials are fat or volutin. The diatoms consumed by fish are Diatoma. Navicula. Cocconies, Synedra, Tabellaria, Meridian, Fragilaria, Nitzschia, Pleurosigma, Amphifileura, Rhizosolenia, Cyclotella, Amphora, Melosira, Aclwanthes, etc.
a)Microcystisb&c) Oscillator,!, d) Anabaenae & f) Spirulna b) Nostoc h) Euglena i) Chlomydomonas j) Volvox k) Spirogyra 1) Nitella.
Zooplankton :
Plankton consisting of animals is called zooplankton. .Zooplankton is abundant in the shallow areas of a waterbody. The zooplankton unlike phytoplankton are particularly distributed horizontally and vertically in an ecosystem. They also undergo diurnal vertical migrations. The zooplankton forms an important group as it occupies an intermediate position in the food web, many of them feeding on algae and bacteria and in turn being fed upon by fishes. They also indicate the trophic status of a waterbody. Their abundance increases in eutrophic waters. They are also sensitive to pollution and many species are recognised as indicators of pollution. Among zooplankton, some of the organisms occasionally occur in appreciable numbers forming swarms. These swarms occur in freshwater ponds forming bands or streaks, or are arranged into areas of thick and thin concentration. Simulating cloud effect, they may give the water a strikingly different colour in the region of the swarm. The most common organisms in zooplankton are protozoans, crustaceans and rotifiers (Fig. 6.2).
a. Protozoa:
Protozoans are most primitive, unicellular and microscopic animals. These organisms are provided with locomotory organellae like pseudopodia, flagella and cilia. These organisms are found abundantly in fish ponds and are useful as natural fish food. Generally protozoans dominate in the zooplankton communities. Protozoans in general, are solitary single celled organisms. In some dinoflagellates and ciliates the daughter individuals do not separate and together form pseudo-colonies during repeated fission. These colonies are called catenoid colonies. The protozoans belonging to the classes sarcodina, flagellata and ciliata are useful as food items to fishes.
The protozoans with pseudopodia are included in the class sacrodina or rhizopoda. Amoeba and Actinophrys are common sarcodines found in fish ponds and are also used as food by fishes and prawns occationally.
The protozoans with flagella are included under the class flagellata or mastigophora. Euglena is the most common fish food organism found in fish and prawn ponds. E. viridis, E. spirogyra and E. minuta are some important species used as fish food. Ceratium, Chilomonas and Phacus are also used as fish food.
The protozoans with cilia are included in the class Ciliata. Here the cilia persist throughout life. The ciliates like Paramecium, Vorticella. Coleps, Colpoda. Metropus, Euplotes. Oxytricha, etc. are fish food organisms. The ciliates are the dominating organisms among the zooplankton.
a) Brachionus plicatilis b) B. rubens c) Euchlanis sp. d) Daphnia cahnata (male) c) D. cahnata (female) f) Moina sp. (male) g) Moina sp. (female) h) Ceriodaphnia sp. (female) i) Artemia salina.
b. Crustacea : The aquatic animals with 19 pairs of appendages and branchial respiration are included in the class Crustacea. The crustaceans vary form microscopic to large animals. Crustaceans form a major component of zooplankton. In zooplankton, the microcrustaceans are useful as food to fish and prawns. The important microcrustaceans are copepodes and cladocerans. The crustacean nauplii also constitute good food material for many fishes and prawns. For example, nauplei ofArtemia are used in prawn hatcheries.
a) Copepoda : These are animals with 5 pairs of thoracic appendages, abdomen without appendages, forked telson, two pairs of antennae and body with head, thorax, and abdomen. The copepodes inhabit many of the freshwater habitats such as lakes, reservoirs, ponds, etc. Many of the copepodes are pelagic and so are abundant in the plankton of both limnetic as well as littoral regions of the water. Only the harpacticoids are mostly benthic or bottom living. The size of the body of the copepods is 0.3 to 3.5 mm. Copepods such as Cyclops, Mesocyclops, Diaptomus, Canthocamptus, etc. are useful as fish food organisms.
b) Cladocera”: The animals which are bivalved, shield shaped with or without shell, flattened trunk appendages and leaf-like caudal styles which may be unjointed or jointed are included in cladocera. The greatest abundance of cladocerans is found near the vegetation in lakes, ponds, etc. The size of these shelled crustaceans varies from 0.2 to 3.0 mm. The cladocerans like Daphnia, Ceriodaphnia, Moina, Sinocephalus, Scapholebris, Sida, Eurycents, Chydorus, Daphniosoma, Polyphemus, Macroihrix. Leydigia, etc. are useful as fish food organisms.
c) Ostracoda : The animals with bivalved carapace, which encloses the entire body, 4-6 trunk appendages and reduced trunk are included in ostracoda. These forms are well represented in both the standing and running waters. These are exclusively planktonic forms. Occasionally the ostracods like Cypris, Stenocypris, et. are consumed by fish.
c. Rotifera : Rotifers are readily identifiable from other planktonic materials by the presence of their anterior ciliated wheel-like structure called corona and hence they are called wheel animalcules. Rotifers live in a variety of aquatic habitats. They are microscopic, ranging from 40 microns to 2.5 mm in size. Usually rotifers like, Keratella, Phlodina, Rotaria. Hexanhra, Filinia, Brachionus Epiphanes, etc., are useful as food organisms. Rotifers offer several advantages as fish feed organisms. They are
1. They reproduce quickly, it is estimated that a population under favourable conditions can double every one to five days. Under intensive laboratory conditions, they have recently been reported to have a doubling rate of less than 9 hours.
2. Rotifers are small and therefore are accepted as food by some organisms that cannot ingest larger zooplankton: thus they are an important first food for many fishes and prawns.
3. They are nutritious and their actual nutritional value can be improved, as can be done for other zooplankton, by packing the rotifers with specific strains of algae or other feed.
Aquatic weeds
Though the aquatic weeds form undesirable vegetation, which cause damage to the fisheries, these are helpful as food for a few fishes. Many herbivorous fishes consume aquatic weeds. The grass carp is a fast growing fish that feeds on aquatic weeds. This fish utilizes submerged weeds like Hydrilla. Najas, Ceratophyllum, Ottelia, Nechamandra. Vallisneria in that order of preference. The young fish prefer smaller floating plants like Wolffla, Lemna, Azolla and Spirodela, the other herbivorous fish utilize aquatic weeds are Pulchellus pulchellus, Tilapia and Etroplus. Though an omnivore, common carp feeds well on filamentous algae like Pithophora and Cladophora. Trichechus sp., a large air-breathing herbivore, is being utilized for clearance of aquatic weeds in the canals of Guyana. The detailed account of aquatic weeds is given in chapter 5.
Annelids
Animals with metameric segmentation, eucoel, nephridia and setae are included in the phylum annelida. The animals which belong to classes polychaeta and oligochaeta are useful as fish food organisms. These are found at the bottom of the waterbody and are generally consumed by bottom-dwelling fish, common carp, catfishes, murrels, etc. Tubiflex, Glycera and earthworms are the common fish food oligochaetes.
Insecta
Animals with 3 pairs of legs, 2pairs of wings, jointed appendages and a chitinous body wall are included in class insecta. Insects and their larvae form the main food item of many fishes. Aquatic insects are often preyed upon by fish like trout, catfishes, murrels, etc. Hemiptera, diptera, coleoptera, ephemeroptera and plecoptera insects dominate as fish food among the insects. Belostomatidae and notonectidae and nymphs of odonata are good fish food organisms. Larvae of mayflies, dragonflies, chironomid larvae, chaoborus larvae and mosquito larvae are also found commonly in fish diets. When mayflies constitute the diet of trouts, it has been observed that the trout are fatter and better flavoured.
Mollusca
The animals with a soft body, shell and foot are included in the phylum mollusca. The molluscans are found at the bottom of waterbody. Hence, only bottom-dwelling fish consume them. The gastropodes are found in the diets of carnivorous and omnivorous fishes.
Amphibia
Amphibians are tetrapodes, terrestrial as well as aquatic. The fishes consume only anuran larvae, the tadpoles among amphibians. The consumption of tadpole larvae is not frequently found.
Fishes
Carnivorous (piscivorous) fishes feed on a variety of other adult fishes, fish eggs. fry and fingerlings. Fishes like murrels, freshwater shark, seenghala, etc. feed on other fishes. The small fishes like Salmostoma, Amblypharyngodon, Puntius, Labeo. Chanda. Nuria, Lebistis, Gambusia. Esomus, etc. are consumed as food by larger fishes. Some fishes are cannibalistic in nature.
Fishes also feed on decapods (prawns). The carnivorous and omnivorous fishes feed on small prawns. For example, Macrobrachium kitsuensis is found in the gut of many fishes. Acetus prawn suspension is given as food to the larvae and post-larvae of prawns in the hatcheries.
The bryozoans or ectoprocta are also found in the gut of fishes. They enter accidentally into the mouth of fishes. Generally bryozoans inhabit the aquatic weeds, stones and pebbles. When aquatic weed are taken as food by fish, along with the weeds the bryozoans enter into the mouth of the fish. Adult bryozoans and statoblasts ofBugula and Hyalinella are found in fish gut. Natural food of different stages of carps like fry, fingerlings, yearlings and adults are discussed in the later part of this chapter.
Significance of Plankton inAquaculture
In temperate countries, because of low-temperature regime, in the place of fertiliser-based fish culture, feed-based intensive fish culture is followed, despite (he heavy expense involved. In the waters of the tropics, a food pyramid exists with bacterioplankton at the base and fish at the top. Plankton provides about 50% of total food required for the fish which can be broadly classified as live food and formulated feed. Live organ-ferns, essentially microorganisms, those drift or are visibly mobile, are referred to as plankton or live fish food organisms in a pond ecosystem. Due to their balanced nutritional content, plank-ters are referred to as ‘living capsules of nutrition. These fish food organisms are broadly catagorised as phytoplankton land zooplankton. The former is com-ijwsed of bacteria and single and multi-• cellular algae. The members of the later ‘. belong to phyla protozoa and metazoa. iSome phytoplankton of interest that iierve as fish food are those of chlorophyceae, cynophyceae, bacillariophyceae, euglenineae and di-noflagellates, and those amongst the zooplankton are protozoans, crustaceans and other aquatic larvae. Plankton, in a pond system, is distributed non-un’rformly and horizontally as well as vertically.Though basically these are surface dwellers, thi.ir daily shrinkage losses are fairly hicjh. Many forms of zooplankters such t.s rotifers, cladocer-ans and copepods, for example, exhibit diurnal vertical migration in response to variation in light intensity.
Thus, plankton can be regarded as a heterogenous group of saline and freshwater organisms, essentially microorganisms, showing no or only vertical movement, drifting helplessly with ;| the water current, i hey are microscopic |; to submicroscopic in size, classified as I euplankton (or hnloplankton; plankton -”: throughout life cycic), pseudoplankton and meroplanklon ipi.iriklon lor a poriod of their life cycles). Some plankton terminology swch as, nekton, neuston, pleuston, etc. baffle a general reader at times. Therefore, these have been elaborated lucidly in the course of the presentation.
This contribution encompasses various aspects of several freshwater fish-food organisms but with the deliberate omission of Artemia as it cannot be regarded as a strictly freshwater species. However, as Tubifex is a conventional aquarium fish-food, some aspects about its culture are touched upon.
Some facts about plankton biology:
1) Transparency optima with reference to plankton in an aquaculture pond are : a) 35-40 cm for 1.2 m deep pond, and b) 25-35 cm for 0.8-1.0 m deep pond;
2) Cat/a adults feed preferably on zooplankton as also almost all fry;
3) Rohu, common carp, silver carp and grass carp feed preferably on phytoplankton;
4) Rohu shows preference to chlorophyceae, as also the crustacean zooplankters;
5) Mrigal feeds on bottom dwellers including plankton, benthos and detritus (neuston);
6) Shrimp feeds upon both zoo- and phytoplankton;
7) Phytoplankton supercedes zooplankton in riverine water as also in a productive pond at a ratio of upto 10:1;
8) Rotifers prefer Cy-anophyceae;
9) Cyanophycean members have a greater adaptability to different environmental parameters, and hence are found in abundance in any water body followed by Chlorophyceae;
10) Some malodour-forming and toxic Cyanophycean members are generally unpreferred diet of certain zooplankters and fish;
11) Some other Cyanophyceans viz., Spirulina, Arthrospira, form the most desired food for all the zooplankters, shrimps and carps;
12) Dominant phytoplankters in a pond system are Chlorophyceae and Cyanophyceae;
13) Similarly, dominant /oopl.mktors are rotifers, copepods and nauplii;
14) Ichthyo-eutrophication: A phenomenon marked by the dominance of phytoplankton in a fish pond system due to overgrazing of zooplankton particularly by catla and other such zooplanktivores as bighead carp (Aristichthys nobilis) and Thai magur (Clarias gariepinus);
15) Cyclomorphosis’. A phenomenon where the same organism exhibits a number of morphological characteristics as the seasons change. For example, Daph-nia, in summer, exhibits a sharp-pointing head and in winter, a round one;
16) In temperate regions, phytoplankton usually grows in a series of flushes or blooms, the first in spring by the increase in sunlight, and in autumn growth is terminated. In tropical regions, growth is nearly uninterrupted subject to continuous availability of nutrients;
17) There may be a seasonal abundance of forms. In summer blue-green algae usually predominate while diatoms are the most abundant in winter;
18) Case study shows that Cyanophycean members dominate from April to November, Chlorophyceans in December and January, Dinophyceans in February, and Euglinineae in March;
19)Plankton blooms may lead to oxygen depletion;
20) Plankton death (senility) leads to ammonia accumulation; and 21) A popular practice to control bloom formation is to add copper
sulphate (CuSo4) and citric acid in the ratio of 1:2, and then apply the mixture at 1-2 ppm (10-20 kg/ ha-m depth).
Classification:
Though there are many classifications of plankton made by several taxonomists, one of them is as au-totrophs (phytoplankton; chemo- and photo-) and heterotrophs (zooplankton; herbivores, “carnivores, detritivores, om-nivores) and as bacteria, a specialised group, that includes both auto- as well as heterotrophs.
According to another widely accepted classification, the three groups are, bacteria, phytoplankton (macroplankton: >3 mm; nannoplank-ton: <0.03 mm; picoplankton: <0.003 mm) and zooplankton (macro: visible to the naked eye, e.g., Anemia’, micro: seen under a microscope; nanno: sub-microscopic; ultraceston: 0.0005-0.05 mm; picoplankton: <0.0005 mm). The last two types of the former and the last three types of the later are commonly collected by centrifugation technique because of their minute size.
Primarily, classification of various types is based on one or the other consideration. Algae, for example, are divided into different divisions on the basis of pigment composition, maintenance of energy reserve, cell wall composition, locomotory organs and their general structures. These contain two main groups of pigments, chlorophylls and carotenoids. The cell wall of algae is composed of cellulose and polysachharides, silica, proteins and lip-ids in various proportions, which also serve as the basis for taxonomic classification.
Thus, the three main groups of plankton are bacterioplankton (a special submicroscopic bacterial-algal group representing mainly the bacteria, nannoplankton and some filamentous algae), phytoplankton (plankton with photosynthetic pigment, of plant origin), and zooplankton (plankton without photosynthetic pigment, of animal origin).
Some of the divisions of phytoplankton (algae) are: euglenophyta (Colacium, Euglena and Phacus), chlorophyta – presence of chlorophyll a and b, cellulosic cell wall, may be unicellular or multicellular (e.g., unicellular: Chlamydomonas’, colonised: Volvox, Pandorina; filamentous: Spirogyra, Ulothrix’, thalloid: Ulva, Monostroma), Chrysophyta (Xanthophyceae – yellow-green algae, chrysophyceae: golden or yellow-brown algae and bacillariophyceae (diatoms) – presence of chlorophyll a and c, xanthophylls pigments, pectin and silica-rich cell wall, cell is covered with a frustule (two overlapping valves connective bands to laterally form a band)), phaeophyta (brown algae); pynrophyta (desmocontae and dinophyceae), rhodophyceae (red algae) and cyanophyceae (myxophyceae or BGA; Anabaena, Nostoc and Spirulina).
Some of the divisions of zooplankton are: protozoa – not a food of choice, indirectly involved in the basic fish-food cycle, unicellular or ncellulnr animals of minute size, usually microscopic, fln-gella and/ or cilia may be present as feeble locomotory organs (e.g., Vorti-ce/la, Actinophrys, Arcella, Diffusia), rotifera (wheel animalcules) (Brachionus, Keratella, Asplanchna, Polyarthra, Fillinia), cladocera -(minute crustaceans of 0.2-0.3 mm) (e.g., Ceriodaphnia, Daphnia, Moina, Simocephalus, Bosmina, Diaphanosoma), Ostracods – small, bi-valved crustaceans (e.g., Cypris, Stenocypris), Copepoda – longest division of Crustacea, body separated into head, thorax and abdomen (e.g., Mesocyclops, Microcyclops, Heliodiaptomus).
Again, based on occurrence, plankton are classified as limnoplankton (occurring in lake), rheoplankton (in running water), haleoplankton (in pond), halioplankton (in salt water), hypalmyroplankton (in brackishwater), and so on. Similarly, based on hydrogrnphical distribution, plnnklon i<; classified as hypopl.’inklon (bottom dwellers), epiplankton (euphotic-zone dwellers), bathyplankton (aphotic-zone dwellers) and mosoplnnklon (dispholic zone dwellers).
Characteristics of plankton as fish food
A pianktonic fish food organism normally has all the required physical trails of an ideal fish-food (or feed), such as a) It has easy availability ; b) it is easy to handle ; c) It performs as a feed; d) Its production cost to serve as feed is low and the rate of capital return is viable; e) It has particle size of 10-500µm dia; f) It stays suspended in the water column for a considerable period (suspendability/water stability); g) It does not pollute the water system; h) It possesses attractability as a feed for the fish; i) It is acceptable, palatable and ‘digestible; j) It possesses a low BOD, reducing any chance of rapid microbial degradation; k) It has an appreciable shelf-life; and I) It is easy for culture/rapid propagation.
Other roles of plankton: Plankton regulates transparency and dissolved oxygen thereby regulating sun’s ray penetration and temperature, and decreasing accumulation of CO,, NHr NO, H,S etc. in water. Pond with a definite phytoplankton is observed to keep prawns calm and reportedly minimize cannibalism. They consume phytoplankton and thereby regulate NH4+ and tieup with heavy metals.
Planton’s role as a bioindicator is worth mentioning. Because of their short life cycle, plankton responds quickly to environmental changes. Hence, the standing planktonic crop and species composition indicate the quality of water mass in which they are found (density>1 lakh in nos/ml water indicates future algal collapse; density <1 lak in nos/ml water indicates future algal collapse; density <50,000 nos/ml water indicates weak algal density; Vorticella microstomata indicates a re-purification zone in a polluted water body; Microcystis bloom indicates a dilapidated water mass). Higher zooplankton population indicates higher organix loading. Planton Plays a significant role in stabilizing the whole pond ecosystem and in minimizing the fluctuations in water quality. Maintenance of proper phytoplankton growth prevents the growth of lab-lab, a bottom meance after its death. Plankton serves as a shelter for a large number of small to smaller creatures when an algal mat (periphyton, and even sewage fungus) is formed.
Indication of algal collaps
Increase in water colour intensity –Clusters of colour on water suface – Milk clouds on water column with foaming/frothing – Water clear-up – Dramatic increase in transparency.
Procedure for enhancing pond plankton population
During preparation of the following procedure is suggested:
Water may be filled upto 50 cm depth – Fertilisation may be done with 9 kg urea and 0.9 kg TP (Total phosphorus) – Pond may be temporarily sealed till dark brown colour with yellowish colouration appears- Water may be filled upto 80% of the operational level and 14kg urea and 1.4kg TP may be applied – Pond kept undisturbed for 2/3 days-(If no colouration develops 50-100kg/ha CaCo3 may be applied) – Pond filled to operational level – 19 kg urea and 3kg TP per ha may be applied – If yellowish-brown coloration does not appear water level may be dropped by 10cm and refertilised with 6.8 kg urea and 0.7 kg TP.
After 5 days, a Secchi disc reading of 25-35 cm and a yellowish-brown water coloration confirm optimal condition for best stocking results.
Nutritional value of plankton (fish food organisms): As discussed earlier, due to their balanced nutritional aspects, fish food organisms are rightly referred to as ‘living capsules of nutrition’ and more often so as single cell protein. However, the nutritional values of each organism greatly vary according to the culture conditions as well as the phase of growth during the harvest. As for example, harvest at prime phase of microalgae contains high protein and at stationary phase, higher carbohydrate. The proximate composition and nutritional details of some natural food groups of the plankton species (Table 1 at P.56) are discussed.
Microalgae: The nutritional status depends on the cell size, digestibility, production of toxic compounds and biochemical composition. Although marked differences are exhibited, the range for the level of protein, lipid and carbohydrate are 12.0-35.0%, 7.2-23.0% and 4.6-23.0%, respectively on dry weight basis. Microalgae could be considered as a rich source of highly unsaturated fatty acids (HUFA) and ascorbic acid (0.11-1.62% dry wt).
Cladocerans: It has low essential fatty acid contents, particularly HUFA. Daphnia contains broad spectra of digestive enzymes, such as, proteinases, pepti-dases, amylases, lipases and even cel-lulases, which ultimately facilitate extrinsic digestion in the predator fish.
Copepods: these contain 44-52% protein and a good amino-acid profile with the exception of methionine and histi-dine.
Dangers to fish food organisms:
The various danger elements that fish food organisms in particular and plankton in general encounter in a pond system include predators such as protozo- fans, rotifers, crustaceans, bacterioph-”fages, vibrios, and even microplanktonic flarvae of benthic organisms, opportunistic pathogenesis by viruses, bacte-fria and fungi, physico-chemical factors f^such as the pH, temperature regime, tur-fbidity, nutrient status of the water and fsediment, as also some of the hydro-fbiological factors such as excessive feeding of one type of the plankton by fish that may, as discussed earlier, lead to ichthyo-eutrophication, etc.
Some cyanobacteria and other plankton reportedly produce toxin, which endanger aquatic life in general and fish in particular. One such example is microcystin production by Microcystis sp.
In India, though the case has not yet been alarming, its potential as a hazard cannot be ruled out. Sometimes, the algal culture may get contaminated with toxic substances such as heavy metals and non (or low) biodegradable pesticides, which may lead to further complications, including algal collapse, oxygen depletion and fish kill.
Food and feeding of cultivable fishes
Thorough knowledge of food and feeding habits of culturable fish is essential for successful fish farming. Mixed farming of compatible species of fish in suitable proportion is practiced for full utilization of food habits of cultured fishes. It is necessary to determine the stocking rate of fishes in ponds. We should also be familiar with food preferences and acceptable food in an emergency for individual species. Frequent feeding zone of individual species and availability of food in each zone of ponds provide important information necessary for successful fish farming.
The food and feeding habits of major carp also differ as availability of different kinds of food in ponds varies. Food habits also van- with season, size and age. We have a very meagre knowledge of the food requirements of our culturable species of major carps. Major carps are non-predatory fishes. They have toothless jaws and cannot, therefore, bite their food unlike predatory fishes which have strong teeth to catch the prey. They can, however, swallow food which is crushed with a set of pharyngeal teeth at the throat before it is passed down into the stomach. Their non-predatory habit of feeding is also reflected by a highly coiled intestine as compared to a very short bag like stomach of predatory fishes. Food components of major carps vary in different stages of their life cycle.
Food of carp fry
Newly hatched larvae of about 5 mm have a yolk sac, on which they subsist for at least two days, when they start feeding on organisms found in water. Three to four days old carp fry measuring about 7 mm feed primarily on zooplankton.
Food habits of all the species of major carps are identical at the fry stage. They all start feeding on cladocerans and the animalcules. Cladocerans and rotifiers form the bulk of the food consumed by these young fish. Cladocerans are the most preferred food of carp fry. They are voracious feeders at this stage. A single fry may consume as many as 150 cladocerans within 24 hours. As the yolk sac absorption differs somewhat from one fry to the other, the number of organisms consumed by them varies accordingly.
Carp fry have the ability to choose and eat only selective food. Generally they discriminate plankton and prefer zooplankton as food. Species of Daphnia, Moina. Cyclops, Diaptomus, Brachionus, Keretella, Fi/i/niaandNauplius larvae form the most important components of zooplankton food. When these organisms are scarce, carp fry may consume plankton algae like Pandorina, Volvox, and Microcystis as an emergency food. Carp fry raised on phytoplankton alone is very weak and the survival is very poor. Phytoplankton have very little food value so far as carps are concerned. Phytoplankton organisms have a resistant cell wall, which is indigestible by tender fry. Zooplankton specially cladocerans are consumed eagerly and also digested quickly.
Food of carp fingerlings
As the young fry of major carps approach toward fingerlings size, there is definite change in their food and feeding habits. Also food of fingerlings differ from one species to the other. Each species of major carps at this stage have a choice for its own preferential food. However, there is only little change in food habits of catla fingerlings which continue to feed largely as before on cladocerans and other animalcules, making very little, use of microscopic plants floating in water. Rohu fingerlings on the other hand start feeding on microscopic plants, vegetable debris, deritus and mud in addition to few cladocerans. The food of mrigal fingerlings is more or less same as that of rohu. but they consume relatively larger quantities of decaying vegetable debris, phytoplankton organisms, sand and mud. Kalbasu fingerlings mainly feed on vegetable debris and microscopic.plants in addition to few cladocerans, detritus and mud.
Food of carp yearling and adults
Catla do not exhibit any marked change in food and feeding habits even at the yearling and adult stage. At all stages of their growth, their preferred food is largely composed of cladocerans, copepods and rotifiers, although they do swallow algae, vegetable debris and other organisms floating in the water. Rohu consume, at this stage, considerable quantity of bottom sand, mud, vegetable debris and planktonic algae but have very little proportion of cladocerans and other animalcules in their diet. Mrigal at fingerling and adult stages have a common diet as that of rohu of the same size and age, but consume more quantities of organic and vegetable debris, microscopic plants sand and mud. Mrigal feeds mostly on debris and decaying matter. The proportion of animal food in their diet is very poor. Kalbasu at fingerling stage consume more or less same food as that of mrigal of the same size and age. Kalbasu prefers feeding on snails and worms at the bottom of pond in addition to their usual food. Some of the submerged plants like Vallisneria, Potamogewn, Ceratophyllum, Hydrilla and Ottelid at least in the decaying condition are utilized to a limited extent by rohu and mrigal. Of all these plants, Potamogeton, is best relished by carps. Catla, however, does not eat submerged plants to any appreciable extent. Rohu, mrigal and kalbasu may casually include these larger aquatic plants in fresh or decaying condition, but carp raised on these plants do not show satisfactory growth.
Food and feeding habits of prawns
A wide range of feeding habits have been noticed in prawns in nature during their developing stages. The nauplius larvae do not feed at all as they depend on yolk reserves. But protozoea larvae feed voraciously on minute food organisms, mainly phytoplankton viz. Skeletoneria, Chaetoceres, etc. as their oral appendages are not fully developed for the capture of larger food organisms, and they have a simple alimentary system. The mysis stage starts feeding on small animal food organisms, occuring plenty in the ecosystem. During the post larval stages, which follow the mysis stage the mouth parts and chelate legs are fully developed, and from now on, the prawn larvae are capable of feeding on a variety of animals as well as vegetable matter. They then settle down to the bottom and browse on the substratum. Penaeus indicus has been reported to feed on plant material in the younger stages while the older ones prefer predominantly crustacean diet. Algal filaments also form part of the food of this species. P. monodon feed on molluscs, crustaceans, polychaetes and fish remains. P. semisulactus consume large quantities of animal matter viz. polychaetes, crustacean, molluscs, foraminiferans and fishes. Controlled fertilization of culture ponds stimulates the growth of algae and zooplankton and inturn some of the bottom dwelling animals, which are known to be the food of prawns.
The natural food of larvae, from mysis stage onwards, consists mainly of zooplankton such as veliger, trochophore, rotifers, copepodes, very small worms and larval stages of various aquatic invertebrates. In the absence of live food, minute pieces of organic material especially those of animal origin (fish, prawn, crab, molluscs, etc.) are readily eaten.
Non-conventional feeds
In aquaculture. supplementary feeds constitute 50 % of the cost offish production. The cost of available feeds is high and generally, these feeds do not meet the actual protein requirements of growing fish or prawns. Hence, it is imperative to make use of the protein rich and locally available non-conventional feeds.
A number of non-conventional materials suitable in the preparation offish feeds have been identified. The blue-green algae, Spirulinaplatensis. grown in sewage water contain 40-70% protein (on dry weight basis) and sufficient quantities of essential amino acids such as lysine and tryptophan, vitamin BI2, unsaturated fatty acids, carbohydrate and minerals. Unlike the cellulose cell wall of green algae, the mucoproteic constituents of the cell wall of Spirulina platensis are easily digestible. Tapioca leaves have 20-40% protein and a good amount of minerals and vitamin A. The toxic constituent linamarin likely to be present in these leaves, may however, be removed by drying and boiling them. Air-dried leaves of Subabul (Leucaena lecocephald), a recent addition to India contain 33 % crude protein and a variety of amino acids similar to those in prawn waste and fish meal. The toxic mimosine content of the leaves is removed by heating the leaves at 80°C for two days. Aquatic fern, Azollapinnata fixes atmospheric nitrogen at the rate of 2-3 kg/ha/day owing to its symbiotic blue-green algae viz., Anabena azollae. The dried Azolla which has a crude protein content of 27% also finds application in the feeds of pigs and poultry. Mangrove leaves contain 8-18 % of protein in the decomposing state. The associated bacteria of the leaves are also known to increase the protein content besides making them easily digestible. Further, the bacterial flora may also improve the quality of food by providing essential amino acids lacking as such in healthy leaves. Seaweeds such as. Ulva fasciata, Enteromorpha intestinalis and E. compressa (green algae); Gracilaria corticata and G.follifera (red algae) and Sargassum ilicifolium (brown algae) have 15-25 percent protein and a number of minerals which should be included in fish feeds.
Other vegetable components are leguminous seed kernels, groundnut oil cake, rice bran, wheat bran, tapioca flour. Non-conventional animal components include silk worm pupae, trashfish meal, prawn waste, squilla meal, squid meal, chank meat, clam meat, pila meat and slaughter house waste. These have high protein content (50-70 %) and the inclusion of any one or two of these components is essential to enhance the protein content of feeds.
For optimal growth, juvenile and adult fish and prawns need 30-40 % and 40 % protein respectively. A prawn feed containing 35 % protein may be prepared using the animal component (50 %), groundnut oil cake (30 % ) and tapioca flour (20 %) and a fish feed of 40 % protein with rice bran (15 %), groundnut oil cake (15 %), animal component (60 %) and tapioca flour (10 %). Cheaper feeds of varying protein levels could also be formulated and prepared with non-conventional components making use of their protein contents.
The dried and powdered feed components are mixed and the mixture kneaded well adding about 30-50 % of water to form a soft dough. The dough is cooked for 30 minutes in steam under pressure at 1 kg/cm2. The cooked dough is then fed through a pelletiser.
Bioenriched feeds
Bioenrichment is the process involved in improving the nutritional status of live feed organisms either by feeding or incorporating within them various kinds of materials such as microdiets, microencapsulated diets, genetically engineered baker’s yeast and emulsified lipids rich in w3HUFA (Highly Unsaturated Fatty Acid) together with fat soluble vitamins.
Factors to be considered prior to bioenrichment
a) Selection of the carrier or biofeed : This is a very important aspect taking into account the acceptability of the organism and its size. Commonly used carriers and their size ranges are listed as under :
1 Microalgae : 2 – 20 u
2 Rotifers : 50 – 200 u
3 Artemia : 200 – 400 u
4. Moina : 400 – 1000 u
5. Daphnia : 200- 400 u
b) Nutritional quality, digestibility and acceptability before and after enrichment. This requires extensive studies on all commercial species. This study will form a baseline to conclude upon whether to go in for bioenrichment or not.
c) Fixing up the level of the enriching media to be incorporated into the carrier organism. This depends on the nutritional quality of the carrier before incorporation and is also based on the feeding trials conducted in the laboratory.
d) Economic feasibility of enrichment.
e) Purity of the culture of the carrier organism.
f) The other criteria that the carrier should satisfy include,
i) It should be easily procurable.
ii) Culture should be economically viable.
iii) Catchability of the carrier by the target species.
iv) It should be easily reproducible.
Techniques of bioenrichment:
There are essentially two methods which are widely used for bioenrichment, – the direct method, and the indirect method.
1. The indirect method : It is based on the fact that baker’ s yeastcontains a fairly high amount of monoethylenic fatty acids and no w3HUFA, and that the fatty acid composition of rotifers is readily affected by the fatty acids of the culture organisms. A new type of yeast has been developed as a culture organism for rotifers in order to improve upon the nutritional value for fish larvae of rotifers cultured on baker’s yeast (Imada et al, 1979). This new type of yeast designed as co-yeast, was produced by adding fish oil or cuttle fish liver oil as a supplement to the culture medium of baker’s yeast, resulting in higher levels of lipids and w-SHUFA, the essential fatty acid for both marine and freshwater finfish and shellfish larvae. In a similar manner Anemia nauplii and Moina are also enriched with W-3HUFA. This method is so called because live feeds are enriched with w-3 HUFA together with the lipid.
2. The direct method: This method was first developed by Watanabe et al (1982). wherein a homogenate prepared by an emulsion of lipids containing W-3HUFA. raw egg yolk and water is directly fed to the carrier organisms to enrich them directly.
The use of both the methods, direct and indirect will significantly improve the dietary value of live feeds by allowing them to take up from the culture medium not only w-3 HUFA, but also fat soluble vitamins together with lipids (Watanable et al, 1982). Temperature and density of the carriers too dictate the incorporation.
Preparation of enrichment media :
For the preparation of emulsified lipids. the w-3 HUFA concentration in the lipid source should be very high. In an ordinary preparation about 5 gm. of the fish oil is homogenized for 2-3 minutes in a homogenizer or mixer or by vigorous shaking. Proper emulsification is ensured by observing the emulsion under a microscope. The preparation may be stored under refrigeration until use. Ermilsifiers may be added to maintain the emulsion. If not, a violent shaking prior to use reforms the emulsion. The enrichment media may be supplemented with water and fat soluble vitamins like A, D, E and K prior to homogenisation.
Enrichment of Artemia nauplii and rotifers with w-3 HUFA is dictated by two factors – lipid content in the emulsion, and type of lipid source. The amount of lipid source depends on the population density of the carriers, their feeding activity and the water temperature. The nauplii or rotifers are harvested using a plankton net of 60 u mesh size washed with clean sea water or freshwater and fed to the larvae of finfish or shell fish in adequate numbers.
Nutritional Requirements
Carps being the fast growing varieties of fishes are mostly chosen for culture practices in India in fresh waters. The general practice is to provide some starchy foods to these carps to serve as dietary calories. As a result of series of experiments conducted in the country certain balanced artificial feeds have been formulated. To meet the dietary demand of fishes one should know the nutritional requirements of fishes such as proteins, carbohydrates, fats, micronutrients, vitamins etc., besides the knowledge relating to digestibility and utilization of the compounded feeds by the fish for yielding protein as the final metabolized product in intensive fish culture practices.
Proteins
Fishes are efficient converters of vegetable proteins into tasty proteins of high biological value and are able to utilize high levels ofdietary proteins for synthesis, as comparedto other organisms. It has been reported that at 470F Chinnok salmon require 40% casin, whereas the requirement was 55% and 580F. It has also been observed that high protein level (53%) is less effective in comparison to lower level (26.67%) when fed to fry and fingerlings of carps. Level of protein depends upon quality of protein for obtaining optimum growth.
Amino acids which are indispensable in human nutrition have been found to be essential for certain fishes and since their composition is known to the primary factor influencing protein digestion, need for their quantitative requirements by the cultivable fishes could be measured by the qualitative and quantitative distribution of amino acids so that limiting ones can be supplemented by synthetic preparations of complementary proteins resulting in a proper mixture of dietary amino acids for better utilization of dietary proteins. Composition of amino acids in fish flesh which can offer guide lines for their levels in artificial feeds is given in Table – 6.1.
Amino acid composition of Fish and other animal proteins (From the Wealth of India)
Animal Proteins
Fish Meal: Fish meal is the ideal protein item having all the essential amino acids required in fish feeds. It has been reported that fishes feed with fish meal have yielded better results when compared to the fishes fed with soyabeen.
Silkworm pupae: In Japan intensive farming of carps in cages and floats is achived by feeding with silkworm pupae and the conversion rate worked out to 2. It has been revealed that fishes fed on silkworm pupae have yielded better growth when compared to the fishes fed on a mixture of rice bran and mustard oil cake in the ratio 1 : 1. It has been observed that a mixture of animal proteins gave better weight grain and feed conversion than a mixture of plant proteins or any of the proteins tested alone. It has also been reported that plant proteins mixed with 10 to 15% of animal proteins could be utilized as the basic ingredients in formulating the artificial feeds under intensive fish farming.
Plant Proteins
They are deficient in lysine and methionine content, and to avoid aminoacid imbalance need supplementation with animal protein. The most favoured items generally used for carp feeding are different oil cakes, and grain fodders. It has been reported that in the composite fish culture of Indian major carps and exotic carps high fish production has been achieved by using a mixture of rice bran and mustard oil cake in the ratio 1 : 1. The nutritive value of oil cakes and grain feeder is dependent on their quality. The quality of prepared feeds will be reduced when their fact content is 10-20%. The overall protein content will be used when the solvent extracted oil cake and rice bran are used as feeds.
Leaf Proteins: Information regarding the use of leaf proteins in fish nutrition is, as yet, negligible except for somevegetable eating species, but because of their high production and competitive economy in agricultural industries, they may in the near future occupy a prominent place in fish feeds after adequate processing involving separation of pigments, flavour and toxins.
Algae Proteins: Algae constitutes the feed of certain varieties of Cultivable fishes. Chlorella spp. have been found to contain all the essential amino acids and protein of desired nutritional and functional and functional quality can be obtained by selecting the suitable media for their culture and adjusting the harvesting time. It has been noticed that feed pellets made of Chlorella resulted in the higher yields of Oreochromis mossambica.
Single Cell Proteins: the proteins derived from yeast, bacteria, fungi or algae grown on a variety of substrata, which include hydrocarbons like crude oil, gas oil, natural gas, coal, carbohydrates such as cellulose, grain, sulfite liquor, molasses and organic wastes constitute yet another source of protein. It has been reported that satisfactory results are achieved when yeast is grown on liquid hydrocarbons as a substitute for a part of fish meal.
Carbohydrates
They are diets of starch and serve as a major source of dietary calories in artificial feeds. Most of the cultivable fishes like carps and mullets are omnivorous taking in considerable amount of vegetable matter and are therefore, well adapted physiologically to digest starch. Digestibility of starch is reported to be 30-90%. Rice bran and wheat bran which are the main starchy diets used for cultivable fishes are found to the highly digestible. Potatoes can be used as substitute for grain. It has been reported that the digestability of potato starch, xylan and algin as 85, 66 and 53% respectively. The ratio of protein to carbohydrate in the feeding of 1 : 7 or 1 : 8 which gives a wide scope to utilize feeding of cheap carbohydrate diets as long as protein in the natural food is sufficient for growth. While formulating the balance diets, carbohydrate and protein ratio needs a careful manipulation so as to spare the proteins for growth and carbohydrate to serve supplying the dietary calories. The diet of certain fishes is said to be nutritionally complete when it contains 39.9% of proteins and 18.2% carbohydrates with food conversion rate of 1. 4-2. 4:1.
Fats
The fishes cultivated in warm waters utilize the fats in a better way. Stimulation has been noticed in the growth of fishes when cod liver oil is added to the diet. But it is known whether lipids or other components of the oil are responsible for such a type of stimulation of growth. As excess fats get deposited in liver, trout ration is usually prepated with less than 10% fat content. It has been reported that in order to yield better results of growth and to reduce mortality in rainbow trout fatty acids with Omega-3 configuration between 3-10% are required. The increased fish yield was found maily due to accumulation of body fat in sorghum fed fish as long as protein was not a limiting factor. Therefore it is clear that provided the protein component in the diet is sufficient, fats can be advantageously used in carp feeds for gaining added yields as well as sparing proteins for growth.
Micronutrients
The growth stimulating micronutrients cannot be substitute for food but their presence in general required to formulate a balanced diet for improving the protein assimilation. In spite of the presence of proteins, growth rate may be slow due to the absence of micronutrients.
Vitamins
Salmon and trout require all the seven vitamins for their growth. Cultivae carps need pyridoxine riboflavin and pantothenic acid. The carps indicated better results when they werefed with 0.8 mg/kg/day of cobalt, which is a part of vitamin B12 concerned with nitrogen assimilation and synthesis of haemoglobin and muscular protein and addition of 4% fodder yeast. Addition of cobalt chloride increases the survival and growth of cultivable fishes.
Antibiotics
The intensive fish farming results in causing diseases to fishes. The role of antibiotics in stimulating protein metabolism depends upon the quality of diet and best results have been obtained by feeding 20,000 units of terramycin to carps every three days resulting in the growth increase by 9.5% and a fodder saving of 10.5%.
Digestibility
Natural food items of fishes are highly nutritious, reflecting a simple and regular relation between protein, fat, carbohydrate and their utilization, but in case of artificial feed stuff, elaborate experimental analysis have to be carried out to know their digestibility and utilization co-efficients. Digestion co-efficients are generally measured in terms of nitrogen and calories.
Relationship Between Food and Growth
Food supply is the most potent factor affecting the growth of fishes and with sufficient quantity and adequate quality of food, fish attain the maximum size. It is not easy to measure accurately the food intake of fishes.
Some of the food is used to replace the tissues broken down in catabolic processes i.e., to provide for basal metabolism. Basal metabolic rates can be measured by studying the respiration of anaesthetized fish. The activities of fish is influenced by the environmental conditions and requires energy. The energy for these activities is obtained from food. Fish can gain weight only when they eat more food than is necessary to satisfy their basal metabolism and to provide energy for their activity. The fish require particular ration for the upkeep of the routine metabolism known as maintenance requirement. Fish only gain weight from surplus food after fulfilling the maintenance requirements. In case of food shortage, fish lose weight, and in case of starvation the metabolic activities are lowered to some extent.
The use of vitamin B12, cobalt nitrate and extract of ruminant stomach give good results in survival of the major carp fry. It is found that 50 kg B12 and cobalt nitrate in combination with extract of goat stomach enhance the survival of carp fry upto 5%. Addition of yeast, also promotes growth. Yeast along with vitamin B12 and B-complex also enhance the survival rate significantly. The knowledge of conversion rate is very essential for the selection of fish feed. The conversion rate is expressed as a ratio between food consumed for increase per unit weight gained by the body discounting the food requirement by the for its maintenance and energy requirement.
Quality of feed Conversion rate = Weight increase (flesh) 6.8 Supplementary Feeding
In the raising of stable fishery, there is a need for regular supply of sustained and balanced food for growin fish. Suitable food has to be provided for healthy growth of fish. Special food arrangement is required for raising good crop of quality often very necessary. However, artificial feeding of fish in rearing and stocking ponds may not be economical in India at present. Some fattening food may, however, be desirable a few days before the harvesting and marketing of fish. To ensure sustained growth, artificial food has to be supplemented at times of natural food scarcity in ponds.
The food which is added in the pond for better growth of fish is supplementary food. The typical supplementary foods are rice bran, groundnut oil cake, bread crumbs, fish meal, maize power, broken rice, soyabean cake, peanut cake, corn meal, cottonseed oil cake, oats, barley, rye, potatoes, coconut cake, sweet potatoes, guinea grass, napier grass, wheat, silkworm pupae, left-over animal feeds and animal manures.
The kind of extra food depends on the type of fish. For example tilapia eat almost anything including all types of supplementary foods. The silver carp eat only phytoplankton, even at the marketable size.
Supplementary feeds given to different cultivated fishes of diverse feeding habits are:
- Vegetable feeds such as leaves, grasses tubers and roots starches.
- Oil cakes such as mustard, groundnut, til, coconut etc., and other residues.
- Grain fodders like wheat bran, rice, lupine, soyabean, maize, rye, barely etc.
- Feeds of animals origin such as fish flour, fish meal, fresh meat from warm blooded animals blood, poultry eggs shrimps, crabs, mussels, snails etc.,
- Additives such as vitamins and minerals.
Fish may also feed directly on dung applied as manure in ponds. The selection of supplementary feed depends on number of factors such as:
- Ready acceptability to fish
- Easy digestibility
- High conversion value
- Easy transportability
- Abundant availability
Of all these, ready acceptability by the fish and its conversion ration and the involved costs are the most important. It should be a balanced one with adequate protein, fat, carbohydrate, mineral and vitamin contents. The rate of food conversion depends on:
- quality of supplementary feed
- stocking density of fish
- size and age of the fish stock
- environmental factors such as temperature, oxygen tension, water etc.
- The method of feeding (the spreading and frequency of distribution etc.)
In the raising of stable fishery, there is a need for regular supply of sustained and balanced food for growing fish. Suitable food has to be provided for healthy growth of fish. Special food arrangement is required for raising good crop of quality often very necessary. However, artificial feeding of fish in rearing and stocking ponds may not be economical in India at present. Some fattening food may however, be desirable a few days before the harvesting and marketing of fish. To ensure sustained growth, artificial food has to be supplemented at times of natural food scarcity in ponds.
The food which is added in the pond for better growth of fish is supplementary food. The typical supplementary foods are rice bran, groundnut oil cake, bread crumbs, fish meal, maize powder, broken rice, soyabean cake, peanut cake, corn meal, cottonseed oil cake, oats, barley, rye, potatoes, coconut cake, sweet potatoes, guinea grass, napier grass, wheat, silkworm pupae, left-over animal feeds and animal manures.
Relationship between supplementary feed and fish production in different culture systems
In the natural environment, when the growing fish number and natural fish food organisms are in equilibrium, it is need not necessary to provide supplementary feed. When the culture system is intended to go in for more fish production, fertilizers and supplementary feeds should be supplied. In the extensive culture system, the fish production can be
Relationship between supplementary feed and fish yield.
enhanced by adding little amount of organic and inorganic fertilizers, whereas in semi-intensive culture systems the fish production can be enhanced by adding the fertilizers along with sufficient amount of supplementary feed. In intensive culture systems the fish production can be enhanced more by using large amount of supplementary feeds (Fig).
The fish yield can be enhanced by increasing the supplementary feed from the extensive to intensive culture practices (Fig).
Formulated feed
Rearing of spawn, fry and fingerlings until they become stockable size and their subsequent culture in grow out ponds require appropriate and nutritionally balanced diet for enhancing production. This has been one of the essential requisites in the development of aquaculture. The advantages of formulated feeds are:
1. Proper formulated feeds are a replica of exact nutritional requirement of fish. Therefore, by understanding the nutritionally well balanced feeds which could be formulated using low cost feed stuff availability locally.
2. Ingredients of formulated feeds can complement one another and raise the food utilization rate.
3. Proteins can supplement one another so as to satisfactorily improve most of the essential amino acid content of the feed, thereby raising the protein utilization.
4. Large quantities of feeds can be prepared at a time with good shelf-life so as to be convenient to preserve, which can be used at the time of supplementary feeding.
5. Feed ingredient sources can be broadened with preferred and less preferred ingredients along with additives like antibiotics and drugs to control fish diseases.
6. High efficiency of feed can be achieved by judicious manipulation of feed ingredients and can be made commercially feasible.
7. By adding a binding agent to produce pelleted feeds, the leaching of nutrients in water is diminished and wastage is reduced.
8. Dispersing over large farm areas is quite possible as formulated feeds are convenient to transport. These are suitable for automatic feeding, for which automatic feed dispensing devices could be successfully employed.
Formulated feed are mainly of two types. They are:
a) Suspension – It is liquid feed, prepared with Acetes, Squilla and clams. Its preparation is discussed in chapter VG.
b) Pelletised feed – This is a nutritionally well balanced solid feed and can be used off the shelf as and when required. This type of feed contains only ingredients of precisely known composition and for this reason such diets are very expensive.
Formulation of feeds:
Though natural fish food is available to fish, supplementary feeds are required to get more yield. The supplementary feed is a combination of different ingredients both from plant and animal origin and it can be administered in different forms. The conventional method is by broadcasting the feed in dry powder form in the fish pond. Broadcasting has its own disadvantages. Much of the feed is likely to be wasted by getting dissipated in water due to the disturbance causes during the feeding of fish. Further, supplementary feed in powder form can not be stored for a longer period. Alternatively, the feed is given in paste form. To avoid the instability of these ingredients, the feeds are now prepared into dry type of pelleted feeds. Dry pellets are easy to handle and store, have longer shelf-life and are free from accumulation of lethal toxic materials like alpha-toxins. Further, such pellets reduce wastage on feeding and ensure uniform composition of the various nutritional components. Owing to these advantages, the fish culturists are assured of maximum return when they use dry pellets.
The ingredients used for formulating fish-feed should be based on their qualities such as protein content, energy level, type of amino acids, etc. Major ingredients commonly used are corn meal, groundnut oil cake or mustard oil cake, soyabean powder, rice bran, wheat bran, fish meal, fish offal, shrimp meal, crab meal, blood meal, slaughter-house waste, tannery waste, silk worm pupae, cow dung, tapioca flour, wheat flour, wild leguminous seed kernels, dried algae, molasses, etc. Besides, dried yeast in the form of flour also serves as a rich food ingredient with protein and many B-group vitamins.
In many fish feeds, protein is the most expensive portion and is invariably the primary substance. The energy level of the diet is adjusted to a desired level by the addition of high energy supplements, which are less expensive than protein supplements. The rectangle method is an easy way to determine the proper dietary proportions of high and low-protein feeds for use in the dietary requirements of fish. For example, if rice bran and groundnut oil cake are to be used as chief ingredients to prepare fish feed with 40% protein, the procedure is as follows: A rectangle is designed and the above mentioned ingredients are put on the two left corners along with their protein contents.
The desired protein level of feed is placed in the middle of the rectangle. Next, the protein level of the feed is subtracted from that of the already used ingredients placing the answer in the opposite corner from the feed. This could be elucidated by an example. That is, for the preparation of 36.8 kg of fish feed with 40 percent protein, 3.5 kg of rice bran and 33.3 kg of groundnut oil cake are added. In other words, for the preparation of 100 kg of fish feed with 40 percent protein, 9.5 kg of rice bran and 90.5 kg of groundnut oil cake are needed.
Preparation of pelleted fish feeds:
The required quantities of the various components are dried, powdered and mixed. The mixture is kneaded well adding minimum quantity of water to form a soft dough. The dough is then cooked for 30 minutes in steam under pressure at 1 kg/cm2 (15 lbs/inch2). The dough after cooking is allowed to cool in a spacious tray and the prescribed quantities of chap fish oil or vegetable oil and vitamin and mineral mixture are thoroughly mixed in the dough. Finally, it is pressed through a hand pelletiser having a perforated disc with 2 mm or larger holes depending on the size requirement for different finfish and shellfish. A semi-automatic pelletiser powered by a 0.25 HP electric motor suitable for the production of pelleted fish feed having a rated output of 10 kg/hr has been designed. The noodles are dried in the sun and broken into pieces of about one cm, Care should be taken to see that the pelleted feeds are free from moisture. However, a maximum moisture content of 15% may be allowed in the pellets. Sun-dried pellets can be stored for a period of even one year.
Management of feeding
Proper management of feeding in aquaculture practice is important for resulting in maximum yield, feed utilisation efficiency and to reduce the waste of feed as well as the cost incurred for feed to a certain extent. The management of feeding involves the feeding rate as well as the frequency of feeding at a fixed place and fixed time. These feeding rates and feeding frequencies vary with the species, size of fish, water temperature and dietary energy levels in the feed (Chiu, 1989). Usually the feeding rate is adjusted either at a given percent of body weight. The former feeding rate is very common and prevalent. Feeding frequency is also positively related to the growth of fish. Fish either at short food chain at low trophic niche or at the higher feeding regime naturally grow faster although there is a maximum ingestive limit at which the increase in growth is negligible. This is defined as the optimal feeding frequency which differs from size offish, sex, gut morphology of the species and meal size of the artificial feed.
The feeding management concept of fixed quantity and quality is to be oriented as the daily food consumption in fish is variable. Such daily variations in feed intake is bound to influence the digestibility of the fish. Hence, the management of feeding schedule should match with the diurnal variations of digestibility of the fish for proper feed utilization and assimilation efficiency. Therefore, mixed dietary regimes of low and high protein in feeding can provide a means of reducing feed costs and marginal cost of fish yield.
Supplementary feeding in nursery ponds
Though carp hatchlings predominantly feed on minute plankton, yet the supply of supplementary feed in the form of finely powdered 1:1 ratio of groundnut oil cake and rice bran to the hatchlings or fry results in better growth in nursery pond. The nursery ponds are supplied with supplementary feed equal to double the weight of spawn from the first to fifth day and then the amount is doubled till fifteenth day. Feeding should be stopped a day before harvesting. The feed should contain 40-45% protein, 25-30% carbohydrate. Cobalt in minute quantities of 0.01 mg/fish/day along with supplementary feed enhances the survival and growth rate of hatchlings. The mixture of silk worm pupae, groundnut oil cake and wheat bran in rohu and mrigal, and soyabean in catla cultures gave good results.
Supplementary feeding in rearing ponds
The fry are provided with supplementary feed in the form of groundnut oil cake and rice bran at the rate of 1% of the body weight till they grow to fingerlings.
Supplementary feeding in stocking ponds
The supplementary feeds like oil cake and rice bran must be supplied to the fish in stocking ponds. Oil cakes like mustard or groundnut and rice bran in 1:1 ratio should be given to fish daily at the rate of 1-3% of the body weight. Aquatic weeds are given to grass carp. Feeding is carried out preferably in the morning hours. It is always better to assess the density of plankton before feed is supplied. If the plankton is below 2 ml/50 1, only then the supplementary feed should be given. The feed should be supplied at a fixed place in a tray suspended in the water. The grass carp should be given aquatic weeds on a bamboo platform.
Summary
A variety of natural fish food organisms are found in a waterbody, which depend on the nutritive nature of the waterbody. The natural food provides the constituents of a complete and balanced diet.
The natural fish food organizims are plankton, oligochaetes, insects larvae, molluscs, tadpoles, weeds, etc.
The plankton is divided into two main categories – phytoplankton and zooplankton.
The phytoplankton drift about at the mercy of the wind and water movements. Algae consist of three major classes which form the main food in phytoplankton. These are chlorophyceae, cyanophyceae and bacillariophyceae.
The most common organisms in zooplankton are protozoans, crustaceans and rotifiers
Bioenrichment is the process involved in improving the nutritional status of live feed organisms either by feeding or incorporating within them various kinds of materials such as microdiets, microencapsulated diets, genetically engineered baker’s yeast and emulsified lipids rich in w3HUFA (Highly Unsaturated Fatty Acid) together with fat soluble vitamins.
Food supply is the most potent factor affecting the growth of fishes and with sufficient quantity and adequate quality of food, fish attain the maximum size.
The food which is added in the pond for better growth of fish is supplementary food. The typical supplementary foods are rice bran, groundnut oil cake, bread crumbs, fish meal, maize powder, broken rice, soyabean cake, peanut cake, corn meal, cottonseed oil cake, oats, barley, rye, potatoes, coconut cake, sweet potatoes, guinea grass, napier grass, wheat, silkworm pupae, left-over animal feeds and animal manures.
Formulated feed are mainly of two types. They are:
a) Suspension – It is liquid feed, prepared with Acetes, Squilla and clams. Its preparation is discussed in chapter VG.
b) Pelletised feed – This is a nutritionally well balanced solid feed and can be used off the shelf as and when required. This type of feed contains only ingredients of precisely known composition and for this reason such diets are very expensive.
Source: AquaCulture