Artificial Feed in Fish Culture

Artificial Feed in Fish Culture• Fishes are widely distributed in various lakes, rivers, ponds, and reservoirs.

• Most of the freshwater fishery resources are very productive and fish growth depends on the availability of as fish natural food organisms.

• Since reproductive potential of fish is very high, they grow fast in their free water bodies.

• For this purpose only commercial species of fish are scientifically cultured using quality and balanced artificial feed fortified with vitamins, minerals and other organic compounds.

• Sustainable and successful freshwater fish culture on scientific basis principally depend upon the use of nutritionally adequate, economically viable and environmentally friendly artificial feeds.

• Since the feed costs vary between 40 and 65 per cent of the total managerial expenditure in freshwater fish culture systems

• artificial feeds must be scientifically formulated and adequately supplied so that the entire amounts of nutritional inputs in the feeds may be utilized by the fish.

Importance of Artificial Feed• Though natural food contributes to the nutrition of the cultured fish in

semi-extensive and extensive fish culture systems, the exogenous supply of artificial food needs to supply nutrients which maybe deficient in natural food.

• Fish production from these systems depends on the natural biogenic potential on the quality and quantity of natural food production in the pond and artificial feed supplied and on the physico-chemical factors of water and soil.

• In intensive fish culture systems, where very high stocking densities are maintained (such as cage culture, recirculatory and pond culture systems), the cultured fish has to rely on the artificial feeds.

• At high densities, insufficient feeding leads to poor growth and nutritional diseases.

• Therefore, it is necessary to design and prepare artificial feeds in balanced proportions with all essential nutrients so that the metabolic activities of fish may accelerate immediately after feeding.

Energy in Artificial Feed• The basic function of fish food is to supply adequate energy for

growth and reproduction.

• There are two advantages in energy utilization of fish such as (1) the excretion of waste nitrogen requires less energy in fish than in land animals and (2) fish do not expend energy to maintain body temperature different from that of their environment.

• In case of warm-blooded animals, energy converts ammonia to less toxic metabolites. But in fish, ammonia diffuses into the water through gills.

• However, it has been found that deficient or excess dietary energy levels results in reduced growth of fish.

• Generally energy is obtained from carbohydrates, proteins and fats and the gross energy levels of these food items are 4,100,5,650 and 9,450 IC cal/kg, respectively.

• The digestible energy is defined as the gross energy of the

food consumed by the fish and is expressed as K cal/kg.

• However, the digestible energy values of non-leguminous

carbohydrate, leguminous carbohydrate, plant protein, animal

protein, and fat for fish are 3.0, 2.0,4.25,3.8 and 8.0 K cal/g,

respectively.

• If the proximate compositions of feed ingredients are known,

the digestible energy (DE) of feed can be calculated for

balancing energy levels in artificial feed.

Example Suppose a fish feed has to be prepared by mixing with three

types of feed ingredients (such as fish meal, soyabean and rice bran) in the ratio of 3:3:4, respectively) having the percentages of their proximate composition as shown in Table 9.1

From these data, it is possible to calculate the digestible energy level in 1.0 kg of fish feed in the following way:

• digestible energy values (K cal/g)

• fish meal: 4.25

• soyabean: 3.8

• rice bran: 3.8

Artificial Feed Versus Water Quality • Application of artificial feed affects water quality criteria more

than any other management factors.

• As a result, freshwater bodies produce excessive plankton blooms which use dissolved oxygen.

• Decomposition of uneaten food also results in oxygen demand. Therefore, the amount of fish that can be produced in lentic water bodies is dependent upon the amount artificial feed to be added while maintaining proper water quality enough for fish growth.

• However, the application of artificial feed in fish culture is the most important and expensive item and therefore, the supply of optimum quantity of feed under various environmental factors (such as temperature and dissolved oxygen) is necessary.

• Artificial feeds are used for culture of different species of fish to increase production above that obtained with chemical fertilizers and organic manures.

• Metabolic wastes from feed reach the water, exert an oxygen demand, and provide nutrient for phytoplankton.

• The phytoplankton also exerts an oxygen demand. Therefore, as feed rates increase, the concentration of phytoplankton increased and consequently water quality deteriorates.

• Maximum daily feeding rates of 0,28,56,84, 112,168 and 224 kg/hectare have been established in some fish ponds of U.S.A. When concentrations of dissolved oxygen fall below 2 mg, aeration was supplied at 6.1 kilowatt per hour.

• Strong correlations (r =0 85 to 0.98) were observed between concentrations of dissolved oxygen and feeding rates particularly at dawn. It has been observed that little aeration is necessary at feeding rates of 56 kg/ha or less.

CONT…• Constant aeration at night in ponds with feeding rates of 112

kg/ha/day and above was found to be effective for fish production in significant levels.

• However at higher feeding rates, feed conversion ratios (feed applied/net fish production) increased and fish production steadily declined.

• Deterioration of water quality obviously limits the amount of feed that can be applied with a given aeration regime. Since the cost of aeration is very high for poor farmers, the amount of aeration must be limited. If excessive aeration is applied without any economic considerations to check low dissolved oxygen at high feeding rates, fish production will obviously be limited by large concentrations of ammonia.

Diet Formulation and Manufacture

Introduction • Diet formulation and manufacture are exercises in

compromise between the ideal and the practical. • The perfect feed formulation that meets the nutritional needs

of an animal or fish must always be modified to be less than ideal so that it can be manufactured.

• Similarly, the perfect feed mixture for producing pellets or some other type of feed particle must always be modified to account for the nutritional needs of the animal.

• Thus, feed formulation and manufacture, intellectual and physical activities, must be combined to produce animal diets.

• Together, formulation and manufacture involve the selection and combination of feed ingredient to form a mixture that can be manufactured into a product that delivers the nutrients needed to meet production goals in animal and fish husbandry.

History of Diet Formulation and Manufacture

• Fish diet formulation and manufacture has developed greatly since it began several hundred years ago.

• Prior to the beginning of the 20th century, fish production was mainly extensive, depending on natural food production, often stimulated by pond fertilization, and on supplemental feeding.

• Early studies on trout feeding showed that feeds based on combinations of animal, fish, shrimp, and vegetable meals reduced growth and impaired health (Embody 1918).

• However, when 15% of the feed consisted of fresh liver or kidney, these problems were eliminated.

• Vitamins had not yet been discovered and were not supplemented to early complete diets; fresh liver and kidney supplied the missing vitamins to early feeds.

• In the early stages of diet preparation, biologists investigated the natural diet of trout (which varied somewhat with location and season), enumerating the species of aquatic and terrestrial creatures they consumed, along with the relative proportions of natural prey items in the total diet of the fish.

• They used this knowledge as a guide to arrive at the proper nutritional profile of artificial diets.

• Embody and Gordon (1924), calculated the proximate composition of the natural diet of wild trout.

• The proximate composition was remarkably similar to that of diets fed to young salmon and trout today; i.e., 49% crude protein, 15–16% fat, 8% crude fiber, and 10% ash, expressed on a dry weight basis.

Protein Supplements• protein supplements are feed ingredients having a protein content

above 20%, on an as-fed or wet weight basis.

• There are three general groups. The first group is made up of ingredients having a protein content of 20–30% which contain materials of plant origin that are by-products of the brewing and distilling industries, wheat germ meal and corn gluten feed.

• The second group is composed of ingredients having a protein content of 30–50% and includes the oilseed meals, crab meal, and dried milk products.

• The third group contains ingredients of over 50% protein and includes fish meals, blood meal, feather meal, tankage (a fertilizer or animal feed obtained from the residue from tanks in which animal carcasses have been rendered), meat and bone meal, yeast products, shrimp meal, poultry by-product meal, soy protein concentrate, wheat gluten, corn gluten meal, and casein.

Animal By-products

• Animal by-products are derived from the meat-packing, poultry processing, and rendering industries.

• The protein content of these products after drying ranges from 50 to over 85%, and there are established standards for the quality of the proteins, generally a minimum pepsin digestibility level.

• The essential amino acid composition of animal by-products meal is similar to that of whole-egg protein, which is the standard by which protein quality is judged.

• These meals are good sources of lysine but poor sources of methionine and cystine, which are usually found to be limiting in diet formulations.

Meat Meal and Meat and Bone Meal.• These products are dried mammalian tissues, exclusive of hair,

hooves, horn, hide trimmings, manure, and stomach contents.

• The protein content of meat meal is about 51%, while that of meat and bone meal is closer to 50%.

• Fat levels in these products average 9.1–9.7%.

• The principal difference between the two products is the phosphorus level, with meat meal having, by definition, less than 4.4% phosphorus.

• The calcium content of meat and bone meal ranges from 8.8 to 12%, while meat meal generally contains about 3% less calcium.

• Both ingredients have relatively high ash contents, about 27 and 31% for meat meal and meat and bone meal, respectively

Blood Meal• Blood meal is a dry product made from clean, fresh

animal blood, exclusive of all extraneous materials. • The most common blood meal is produced by spray-

drying after an initial low-temperature vacuum evaporation has reduced the moisture content to about 70%.

• Other processes of drying blood include flash-drying and conventional drying in a cooker.

• Blood meal has a minimum protein content of 85% and a lysine content of 9–11%, with a lysine availability of over 80%.

Feather Meal• Feather meal is made from poultry feathers, which

have been hydrolyzed under pressure in the presence of Ca(OH)2 and dried.

• It has a protein content of 80–85%, and not less than 75% of the protein must be digestible by the pepsin digestibility method.

• Its use in fish feeds is restricted, however, due to its low protein digestibility by fish [52.4–70.5%, (NRC 1981)].

• Recent investigations have shown that the protein digestibility of feather meal may be higher for rainbow trout

Poultry By-product Meal.• Poultry by-product meal is made from waste generated from

poultry processing plants, exclusive of feathers and the contents of the gizzards and intestines.

• The material remaining after chickens are dressed is rendered and dried.

• The ash content cannot be higher than 16%, of which not more than 4% can be acid-insoluble ash.

• Regular poultry by-product meal contains about 58% protein and 13% fat on an as-is basis.

• Pet-food grade and low-ash poultry by-product meals contain higher protein and lower ash levels than regular poultry by-product meal.

Milk By-products• Several milk by-products are useful in the formulation of fish

feeds, including dried whey, dried whey product, casein, and dried skim milk

• Dried whey product is the residue obtained when a portion of the lactose has been removed, while dried whey contains a minimum of 65% lactose.

• The protein content of whey products is relatively low (13–17%), yet these products are classified as protein supplements.

• Dried skim milk is sometime used in starter diets, due primarily to its excellent digestibility and amino acid balance.

• Its protein content is about 34%. • Casein is the residue obtained by acid or rennet coagulation of

defatted milk. • By definition, it contains at least 80% protein. • Vitamin-free casein is the standard protein supplement used

in semipurified diets.

Gelatin• Gelatin is an important ingredient in semipurified

feed formulations (NRC 1993). • It is a glutinous material obtained by the partial

hydrolysis of collagen from animal skin, tendons, and ligaments.

• It is hard and brittle when dried but dissolves in hot water and forms a jelly when cooled.

• It is 88–92% protein and contains almost no tryptophan.

• It is used in semipurified diet formulations as both a protein source and a binding agent.

Fish Products and By-products• Fish meal is the most important protein ingredient used in

diets of salmon, trout, shrimp, and marine fish.

• The major fish meals include anchovy, capelin, menhaden, sand eel, herring, whitefish, and salmon.

• They may be made of whole fish, as is the case with anchovy, capelin, or menhaden, or from processing residue, as is the case with whiting, pollock, herring, and salmon.

• Fish meal contains high levels of essential amino acids.

• The fat content ranges from 4 to 20%, and the ash content is highly variable, ranging from about 11–12% in anchovy meal to over 23% in whitefish meals made from filleting wastes.

• Typical specifications for fish meal for use in salmonid diets are listed in Table 9.6.

• The waste products of shrimp and crab processing can be dried to produce shrimp and crab meal.

• These products contain about 40 and 32% protein, respectively.

• Their ash content is high because of the quantity of shell that remains in the waste after processing.

• These wastes are good sources of trace elements and carotenoid pigments.

Wet Fish Products.• Fish waste may be preserved by means other than drying, such

as acid preservation.

• When it is acid-preserved before hydrolysis, it is called fish silage.

• When it is hydrolyzed and then acidified for preservation, it is called fish hydrolyzate.

• Either mineral or organic acids can be used as the acidulent as long as the pH of the material remains low (<4.0) and antifungal agents are added.

• During acid preservation, the proteolytic enzymes present in the waste material hydrolyze the fish protein, releasing water from peptide bonds, resulting in a liquid product.

Wet Fish Products

• Short-time, high temperature exposure will denature the enzymes and stop hydrolysis.

• Fish silage or hydrolyzate can be used as is, concentrated, or dried with other ingredients.

• Wet fish can also be pasteurized by heating to >85◦C for 15 min and used directly as an ingredient in semimoist diets.

Plant Protein Sources• The most important protein supplements of plant

origin are the oilseed meals, produced from the cake remaining after oil has been extracted from soybeans, cottonseed, canola, peanuts, sunflower seeds, coconuts, and so forth.

• Oils may be mechanically expelled or extracted by solvents.

• In North America, soybean meal is the most commonly used oilseed protein.

• Dehulled soybean meal contains 48% protein, while defatted soybean meal contains 44% protein

Plant Protein Sources• Soybeans contain several antinutritional factors that are

important considerations in fish nutrition.

• Some, such as the trypsin inhibitors, can be inactivated by heat, while others, such as phytic acid, are unaffected by heat.

• Phytic acid can reduce zinc availability and reduce protein digestibility in salmonid diets

• Full-fat soybean meal is obtained by processing raw soybeans from which no oil has been removed and is sometimes used in trout and grow-out salmon feeds

• Its use is restricted in catfish feeds because of its oil content.

• It is not suitable in juvenile salmon diets.

Plant Protein Sources• Cottonseed meal has been used in the OMP formulation at 15% due

to its protein content (48%) and its value as a binder. • Cottonseeds, like most oil seeds, contain antinutritional factors that

must be taken into account when considering their use in fish diet formulations.

• Wheat gluten and corn gluten meals are protein supplements of plant origin that are derived from grains.

• Both corn and wheat gluten meals are by-products of starch production and are high-protein ingredients (>60 and >75% protein, respectively).

• Wheat germ meal is a by-product of wheat milling and consists primarily of the germ of the wheat seed, with some wheat middlings and bran added.

• It has a variable proximate composition, depending on the milling processes used.

• The protein content varies from 25 to 30%, while the fat level varies from 7 to 12%.

Plant Protein Sources• Brewery and distiller’s by-products are another

major category of protein supplements of plant origin.

• These products are made from the residue remaining after beer and liquor production.

• Since most of the starch in the original material is fermented to alcohol and removed, the protein and fiber content of the by-products is increased on a relative basis.

• Distillers’ products are enriched with vitamins and nucleotides as a result of synthesis by yeast.

Plant Protein Sources• Brewer’s dried grains and brewer’s yeast are the major by-

products of brewing that are sometimes used in fish feed

formulation.

• The protein and fiber contents of brewer’s dried grains are 27 and

13%, respectively.

• Brewer’s dried yeast contains about 44% protein and only 3%

fiber.

• Brewer’s grains have limited use in fish diets because of their

bulk and the difficulty in grinding them to a consistent particle

size.

• Brewer’s yeast acts as a binder in some formulations, but its use

is limited because of its relatively high cost.

Plant Protein Sources

• A fourth group of plant protein supplements includes the pulses,

e.g., peas, beans, and lentils.

• These products contain 20–30% protein, but their methionine

levels are low, limiting their use in fish diet formulation.

• The protein fraction can be concentrated by air classification,

resulting in protein concentrates having 50–60% protein.

Other Protein Sources• Another category of protein supplements is sometimes referred

to as unconventional feedstuffs. • These products have not yet reached the level of availability or

acceptance that allows them to be used routinely in fish feed formulations, but someday they may.

• They include single-cell proteins derived from yeast or bacteria grown on waste material such as paper mill sludge, sewage, crop processing wastes, and methane.

• The microorganisms are then harvested, purified, and dried into a product suitable for animal feeding.

• Products with 60–70% protein have been developed, and feeding trials with salmonids in which single-cell protein derived from yeast has replaced fish meal have been promising

• Some concern has been raised about the digestibility of yeast products by salmonids and about the possibility of uptake of heavy metals and other undesirable compounds by single-cell organisms grown on industrial waste.

Other Protein Sources• Krill, Euphausia superba and E. pacifica, is a major marine

biomass that is increasingly being harvested and processed into supplements for fish feeds.

• Krill meal is 33–55% protein, 15–20% fat, and 15–28% ash.

• Besides having a well-balanced amino acid profile, it contains the carotenoid pigment, astaxanthin, which is the natural pigment that colors the flesh of salmonidsand the skin of many species of fish.

• In feeding trials, fish fed diets containing krill meals have grown nearly as well as those fed conventional diets

• Krill meal and krill hydrolyzates are added to salmon fry and fingerling diets to increase diet palatability

Other Protein Sources

• A final unconventional ingredient category is dried insect meal.

• Most fish nutritionists, at some time in their careers, will be asked by a fish farmer if it is feasible to grow fly larvae or worms with which to feed fish.

• After all, are these not natural feeds for many fish?

• Studies of insect meals suggest that hey have relatively high nutritional values .

• In general, it is simply not cost-effective to produce them, but in some instances, ingredients such as silkworm pupae and maggot meal can be economical ingredients to include in fish diets.

Energy Sources

Carbohydrates (Starch) from Grains

• Basal feeds, or energy feeds, are low-protein, high-energy feed ingredients.

• The upper limit for protein content of basal feeds is 20%, although most are in the 10–17% range.

• Grains are generally 68–72% starch, with the exception of oats, and about 10–12% protein.

• Domestic animals can digest about 95% of the starch in grains, hence their classification as energy feeds.

• The digestibility of the carbohydrates in grains is highly variable among fish.

• Carnivorous species, such as salmonids, derive very little energy from unprocessed plant starch.

• Omnivorous species, such as catfish, and herbivorous species, such as some carp, derive a high amount of energy from grain starch, providing that it is cooked.

Carbohydrates (Starch) from Grains

• By convention in animal nutrition, energy feeds cannot contain over 18% fiber

• Otherwise, they are classified as roughages.• Fiber is indigestible by carnivorous fish, while

omnivorous and herbivorous fish are able to digest fiber to varying, limited degrees.

• The fiber content of grains is about 6%, although oats and barley contain higher levels, at least hulled varieties.

Carbohydrates (Starch) from Grains

• Numerous by-products of grain processing are used in animal feeds and are also classified as basal feeds.

• Wheat milling, which produces flour as its main product, also produces wheat shorts, wheat bran, wheat mill-run, feed flour (second-class flour), and wheat middlings, all of which can be used in fish feeds.

• By-products of oats, corn, and other grains are also potential fish feed ingredients.

• Due to the removal of starch (flour), these products contain higher protein, fiber, and fat levels than the grain from which they were derived.

• Factors other than nutrient content influence the use of basal feeds in animal diets.

• The most important factor is cost, which is usually relatively low.

• Thus, after the nutrient requirements have been met, basal feeds can be used to fill out the energy needs in animal feed formulation.

• Basal feeds also have excellent binding properties and can help to hold feed pellets together in both dry and semimoist diets.

• Finally, they are relatively indigestible, and this quality is useful in animal production when a reduced rate of growth at a normal feeding level is desired.

• Rarely does a similar situation arise in fish culture.

• A large number of feed ingredients other than those listed here may be suitable for use in fish feed formulation.

• As mentioned earlier, over 18,000 individual feed ingredients have been identified and classified throughout the world.

• Although most of these ingredients will never be used in fish feeds, some are important feed constituents in developing countries.

• Fish nutritionists continue to identify potential fish feed ingredients and characterize their chemical composition and nutritional value to fish.

Fats and Oils• Fats and oils are lipid sources, fats being the term for

lipids that are solid at room temperature and oils being the term for lipids that are liquid at room temperature.

• The melting point of a lipid depends on its fatty acid composition.

• Lipids containing a high proportion of unsaturated fatty acids have a lower melting point than those containing a high proportion of saturated fatty acids.

• Thus, tallow is termed a fat, while plant or fish lipids• are called oils. In either case, they are concentrated

energy sources for fish and animals, having 2.25 times as many calories per gram as carbohydrates, a result of their structure.

• It used to be thought that fish could not digest fats, because they were solid at the water temperature at which most fish are cultured.

• However, research has shown that fats are digestible to fish, although slightly less so than oils

• The main factors determining which lipid source to use in fish feed formulations are the

1. fatty acid composition of the lipid source and

2. its physical characteristics at ambient temperatures,

• which dictate how it must be stored and handled at the feed mill.

• A variety of commercially available fats and oils is suitable as

ingredients for fish diets.

• Salmonid diets normally include fish oils, such as herring,

pollock, menhaden, anchovy, and capelin. Plant oils, such as

soybean, corn, and cottonseed, and animal fats, such as tallow,

lard, and poultry fat, may also be used as long as the diet

contains sufficient levels of essential fatty acids

• Fats and oils are chosen using the same criteria as for other

ingredients: price, availability, nutritional value, and quality, as

defined by chemical tests.

• Since fats and oils are susceptible to oxidative and hydrolytic

degradation, specifications on the percentage of free fatty acids and

products of oxidation, such as malonaldehyde and peroxides, are

generally made.

• Limits on water content, unsaponifiable matter content, and

insoluble matter are also often specified.

• Occasionally, refined fish oils are available on the market; oils are

refined to reduce free fatty acid values and nonfat material.

• Even though these oils are within specifications for fish feed use,

they may be low in naturally present antioxidants, which can result

in a shortened induction period prior to the onset of oxidation.

• Oxidation of fat and oil can be prevented by adding antioxidants.

• Antioxidants are usually added to fish oils during production to prevent oxidation, but buyers of oil for fish feed use should make certain this had been done.

• Ethoxyquin is the most common antioxidant used in fish oils.

• Another concern with fats and oils is the possible presence of organic contaminants, many of which are lipophillic.

• Several published values for polychlorinated biphenyls (PCBs) and 1,1-dichloro-2, 2-bis(p-chlorophenyl) ethylene (DDE) in fish feeds are available , While none of the published values approach toxic levels,

Other Nutritive Ingredients• Practical mixtures of protein supplements and basal

feeds contain all of the nutrients needed by fish but not at levels sufficient to meet their total dietary requirements.

• Thus, additional vitamin and mineral premixes are added to feeds to ensure adequate intake of these nutrients.

• Fats and oils are also added at low levels to reduce dustiness in catfish feeds and at high levels to increase the dietary energy levels in high-energy feeds for salmonids and some marine fish, such as yellowtail.

Vitamin Premixes• Vitamin premixes are concentrates in which stable forms of

essential vitamins are mixed with a carrier, usually a basal feed such as a wheat by-product.

• Choline chloride is not included in vitamin premixes, although it is a stable product, because it has been shown to reduce the stability of other vitamins

• So, it is added to feeds separately. • Ascorbic acid is included in some vitamin premixes but is added

separately to others.• In the past, the concentration of vitamins in the premix was

sufficiently high that the finished feed exceeded the recommended vitamin levels (NRC 1993).

• In recent years, the level of vitamin supplementation has been lowered to match the recommended levels more closely.

• Vitamin premixes are added to practical diets at levels ranging from 0.5 to 4% of the diet, depending on the formulation of the vitamin premix.

Mineral Premixes• Mineral premixes are concentrates of essential elements that are

fortified in practical fish diets to make up for low levels in the formulation or to overcome antagonistic interactions among feed ingredients.

• Trace element fortification is a wise precaution when diets contain high levels of protein supplements of plant origin, which are low in some trace elements and which also may contain phytic acid, which reduces the bioavailability of divalent cations.

• High dietary ash levels can result in antagonistic interactions between calcium phosphate and other minerals, i.e., phosphorus and zinc, which lower intestinal absorption .

• The cost of trace element premixes is low, so including them in practical diets is inexpensive insurance against possible deficiencies.

• .

• Additional mineral fortification is required in

semipurified, experimental fish diets since their

ingredients are highly refined and do not contain

sufficient amounts of minerals to meet the nutritional

requirements of fish.

Nonnutritive Feed Additives• Nonnutritive feed ingredients are additives that are

included in diets for reasons other than to provide nutrients.

• For the most part, these compounds have little or no nutritional value, yet they are important constituents of fish feeds, increasing pellet stability, diet safety, diet flavor, and animal and fish performance and health status and influencing the quality of the final product.

• Nonnutritive feed ingredients include feed binders, carotenoid supplements, drugs and fiber, flavorings, and water.

Pellet Binders• Fish feeds must be formed into particles or pellets that are strong

enough to withstand normal handling and shipping without disintegrating.

• Moreover, fish feeds must be somewhat water-stable.

• These requirements make it necessary for feeds to contain binders.

• There are numerous materials that act as binders in fish feed, including regular feed ingredients and ingredients added solely for their binding properties.

• Some binders are by-products of cereal grains or plants and provide nutrients to the diet.

• For example, 20% pregelatinized potato starch is added to eel diets to increase the water stability of the dough and to provide energy.

• Other commonly used binders include bentonite, lignin

sulfonate, and hemicellulose extract, none of which provides

nutrients to the diet.

• Bentonite is a naturally occurring clay consisting mainly of

trilayered aluminum silicate. It is available as either sodium

bentonite or calcium bentonite.

• Sodium bentonite has, by definition, more than 1% and less

than 2% available ion content, or sodium exchange. It swells

when added to water, while calcium bentonite does not.

Pellet Binders• Moist and semimoist fish food production requires the

use of both nutritive and nonnutritive binder materials.

• Nutritive binders include oat groats (the hulled grains of oat), vital wheat gluten, finely milled wheat bran, cottonseed meal, gelatin, fish hydrolyzates, and pregelatinized starches.

• Nonnutritive binders include tapioca (starch extracted from cassava, brazillian species), carboxymethylcellose, alginates, agar, and various gums.

• Chitosan, carageenan( family of linear sulfated

polysaccharides that are extracted from red seaweeds) and collagen have been evaluated as binders but are not commonly used

Pellet Binders

• Semimoist feeds, containing 25–35% moisture, can often be made into satisfactory pellets by careful selection of feed ingredients that possess binding properties.

• However, when feed formulations contain ingredients that do not possess suitable binding properties, it is necessary to add ingredients specifically to bind the diet.

Pellet Binders

• Moist feeds, having moisture contents of 35 to 70%, always

require the addition of a binder.

• For example, semipurified test diets, such as H440, include

gelatin and carboxymethylcellulose as binders.

• Moist diets, which are combinations of wet fish ingredients and

dry meal, may contain 0.5–2.0% alginates as binders.

• It was found that alginates were better binders than gum,

carageenan, chitosan, collagen, carboxymethylcellulose, and corn

starch in a 41% moisture diet.

• Agar was an effective binder, but expensive.

Carotenoid Supplements

• Addition of carotenoid pigments to fish diets to color flesh and/or eggs

• Over 300 pigments are found in various plants and animals, with xanthophylls and carotenoids being the most important classes of carotenoid pigments that add color to fish.

• For the most part, xanthophylls are found in plants, such as corn, and carotenoid pigments in crustaceans and fish.

• Some finfish and shellfish possess the ability to convert certain xanthophyll pigments to carotenoid pigments.

• Goldfish and common carp can convert the yellow xanthophyll pigment, zeaxanthin, to the red carotenoidpigment, astaxanthin .

• Similarly, Penaeus japonicus, a shrimp, can convert both β-carotene and zeaxanthin to astaxanthin

• Salmon, trout, and red sea bream, which normally have pigmented flesh and skin, do not convert xanthophyll pigments to the carotenoids, canthaxanthin, and astaxanthin.

• In nature, they receive these pigments in their diet. • Fish raised in hatcheries and farms must receive canthaxanthin

and/or astaxanthin in their diets to become pigmented.• Carotenoid supplementation is necessary for salmonid offspring

to produce viable offspring• In nature, carotenoid pigments are synthesized by algae and

bioconcentrated in the food chain, ultimately ending up in fish.

Therapeutants and Nonspecific Immune Stimulants

• Therapeutants are added to fish feeds to treat, cure, mitigate, or prevent disease.

• A number of drugs are effective against fish diseases, although in the United States, the only ones approved for use with fish feed are sulfamethazine, terramycin (oxytetracycline), and furox. Erythromycin and azithromycin have been used to treat bacterial kidney disease in captive broodstock of endangered salmon stocks, but they are not allowed in normal production.

• In Europe, oxalinic acid is used in feeds as an antimicrobial drug.

• As with livestock feeds, medicated fish feeds have specific labeling requirements, including a warning to withdraw for a proscribed length of time before the fish are marketed.

• Antibiotics have been supplemented at subtherapeutic levels for

decades in poultry and swine feeds to stimulate growth.

• Their benefit is derived through control of intestinal microflora,

preventing toxin-producing microorganisms, such as

Clostridium perfringens, from becoming established in large

numbers and lowering the growth rate of the animal.

Nonspecific immune stimulants, (neutriceuticals)

• They are unregulated feed additives that are used to enhance

the health and well-being of farm and companion animals.

• In fish, the focus on neutriceuticals lies in making the fish less

susceptible to infectious disease.

• The most common supplements are β-glucans, which are

fragments of the cell walls of yeast and mycelial fungi.

• β-glucans supposedly come into contact with leukocytes in the

intestinal mucosa.

• Glucans supposedly possess the same chemical signals as

infectious disease agents and, therefore, activate the

leukocytes.

• It physically attach to pathogens and thus render them inactive.

• Although glucans have been shown to reduce fish disease, and also to stimulate the nonspecific immune response of fish, exactly how they work is not known.

• Glucans are sometimes effective, and other times not.

• Questions remain concerning the effective dose, route of administration, and chemical form.

• There are many forms of β-glucans, and other materials that stimulate the immune system of fish.

Nonspecific immune stimulants, (neutriceuticals)

Probiotics• Probiotics are live, microbial feed supplements that are thought

to stimulate animal and, possibly, fish growth by affecting the microbial flora population in the gut of the animal.

• Probiotics may be a single species of microorganisms or a mixture of species.

• The concept behind their use is that the species of microorganisms present in the supplement colonizes the gut and out competes detrimental species of microorganisms, thus limiting their numbers and allowing the animal (fish) to avoid wasting metabolic energy fighting the effects of detrimental microorganisms.

• probiotics must be added to feeds after pelleting.

Enzyme Supplements• Enzyme supplements are either single, purified enzymes or

crude enzyme preparations containing multiple enzymes that are

added to feeds to enhance the digestion of feed components that

the fish either cannot digest or cannot digest efficiently.

• Eg, Phytase , cellulase,

• Enzyme supplements are available to assist in the digestion of

complex carbohydrates, collagen in skin and bones, and other

feed constituents.

• Enzymes are typically denatured at temperatures above 65◦C, so

adding them to feed mixtures before compression or extrusion

pelleting destroys their activity.

• Enzyme supplements are typically sprayed on feeds after

pelleting.

Hormones• The use of anabolic steroids in domestic animal feeds is no

longer permitted in many parts of the world due to concern about hormone residues in food products.

• The same concerns exist for fish products, and the addition of steroids and other hormones to the diets of fish raised for market will almost certainly never be approved.

• there are some aquaculture situations in which the addition of hormones to fish diets for a short period may pose no human health risk and may prove useful to fish culturists.

• Hormones fall into three categories:

i. those that affect growth and feed conversion,

ii. those that affect sexual development, and

iii. those that affect osmoregulation

• Fish growth rates can be accelerated by supplementing diets with anabolic steroids and thyroid hormones, thereby increasing feed intake and metabolic efficiency

• An alternative is to add compounds or feed components that stimulate hormone production or that overcome hormone inhibition associated with certain feed ingredients, notably canola (rapeseed).

• Pituitary growth hormones and insulin may also have growth-promoting effects when added to fish feed

• For example, weight gain increases of over 90% have been observed in salmon fed diets containing low levels (1 mg/kg) of 17 α-methyltestosterone.

• Some species, such as chinook salmon, do not respond as dramatically to dietary supplementation with hormones.

• A 26% increase in growth was achieved with fall chinook salmon when testosterone was fed in the diet.

• Thyroid hormones promote growth of teleost fish in numerous studies

• Physiological levels of testosterone in commercial

salmon feeds, as fish feeds contain fish meals made

from spawning fish, such as herring.

• fish meals made by low-temperature drying of

spawned salmon carcasses contained androgens that

stimulate growth in coho and chinook salmon fry.

• The use of naturally derived products containing

anabolic hormones remains an unexplored avenue of

increasing fish growth rates.

• Hormones are added directly to fish diets to cause

sterility or sex reversal.

• The use of sterile fish in aquaculture is advantageous

because it eliminates precocity and the cessation of

somatic growth that accompanies sexual maturity.

• Sex reversal is currently practiced in species of fish,

such as chinook salmon, when one sex has a desirable

product or qualities, or when control of reproduction

is desired, as is the case with tilapia.

Antimicrobial Agents• Microorganisms require unbound water to grow in foods and

feeds.

• Feeds containing more than 12% moisture can support bacterial, mold, and yeast growth unless they are frozen.

• Microbial growth occurs very rapidly in semimoist feeds, and many molds produce compounds that are toxic to fish.

• In semimoist feeds at room temperature (22◦C), mold growth is visible within 3 days, while at refrigerated temperatures (1–3◦C), it may not be visible for 10–20 days.

• During frozen storage, microbial growth is completely stopped.

• Thus, if semimoist diets are fed to fish shortly after manufacture, there is no need to use antimicrobial additives in the feed.

• If longer storage is required, additives and other strategies must be used to prevent feed spoilage.

• The benzoates and parabens are wide-spectrum antimicrobials, which are effective against bacteria, fungi, and yeast.

• Propionates are used primarily to inhibit yeasts and molds but are also effective against bacteria, fungi, and yeast.

Antioxidants• Antioxidants are chemical compounds that are added to

feed ingredients to control oxidation of lipids.

• Other food components, such as carotenoid pigments and tocopherols, can also undergo oxidation.

• The mechanism of highest concern in feed manufacturing is autoxidation, also known as atmospheric oxidation, which is the oxidation of moderately unsaturated fatty acids, resulting in products that produce off-flavors and off-odors.

• The rate of autoxidation of lipids can be accelerated by an increased radiation level, divalent cation concentration, temperature, and oxygen concentration.

• Antioxidants work by chelating pro-oxidant divalent cations, by

acting as free radical acceptors, or by donating hydrogen.

• The latter two functions are considered sacrificial because once

an antioxidant molecule reacts, it no longer possesses

antioxidant properties and is therefore “destroyed” in the

process.

• Thus, antioxidant concentrations fall during the initiation phase,

and once they are used up, oxidation reactions proceed very

rapidly.

Fiber• Fiber is the nonnutritive portion of feed ingredients that is measured

as crude fiber in proximate analysis.

• It is indigestible by salmonids and other carnivorous fish, but channel catfish have intestinal microflora capable of digesting a small portion of dietary fiber.

• Some herbivorous fish, such as grass carp, derive nutrients from fiber but some, such as Tilapia aurea, do not.

• Fiber is added to semipurified diets to facilitate binding as well as to increase digestion efficiency

• Generally, fiber is not added to practical diets; rather it is avoided because it passes through the fish and adds fecal solids to rearing water and farm effluents.

• This point is critical in aquaculture systems employing water recirculation and in rainbow trout farming, where high volumes of water are discharged into rivers and lakes.

• Upper limits for fiber in feed formulations are generally specified, thus eliminating many potential fish feed ingredients and restricting the levels of others.

• In diets for fish that do not possess the ability to digest fiber, levels of fiber above 3–5% are not recommended (NRC 1993).

• Fiber levels as high as 8–12% are tolerated by most fish, but such levels often result in growth depression (Edwards et al.

• Fish fed diets high in indigestible fiber increase their feed intake and gastric evacuation time, but the extent to which fish can compensate in this manner is limited.

Water• The water content of feeds ranges from 6–10% for

dry-compressed or extruded pellets to 65–70% for high-moisture, wet pellets.

• The moisture content of feeds is important because of the potential for microbial growth in high-moisture feeds, and the moisture content is critical in the pelleting process, where it is added to the mixture as live steam just prior to pelleting.

• Steam pelleting and cooking extrusion increase the moisture content of the feed mixture to approximately 18 and 23%, respectively, but the pellets are dried to <11% immediately after pelleting

• Some fish species accept moist feeds more readily than dry feeds, particularly Pacific salmon fry.

• However, brown trout and turbot grow equally well on moist or dry diets

• In the past, researchers reported that chinook salmon reared in marine net pens grew more rapidly when fed diets containing 15–30% water than when fed dry diets, but improvements in feed formulation and manufacture have eliminated this effect

Flavorings and Palatability Enhancers

• Fish are very sensitive to certain tastes in their feed, a trait that can be both harmful and beneficial in diet formulation and manufacture.

• For example, chinook salmon fry are extremely sensitive to the presence of low levels of dietary soybean meal and respond to its presence by reducing their intake.

• Trout are less sensitive to dietary soybean meal, although in semipurified diets, the addition of a “fishy” component to the diet to mask the taste of soybean meal must sometimes be made to induce trout to consume feed

Artificial Feed Versus Fish Health• In different types of farming systems fish obtain dietary

nutrients from available pond food organisms and nutritionally complete diet throughout their life cycle.

• Dietary imbalances may arise from the presence of disproportionate levels of amino acids, fatty acids, minerals, and vitamins in foodstuffs and have resulted in manifestations of several nutritional pathological conditions such as scoliosis, eye cataract, fatty liver, exophthlmous and skin/fin haemorrhage.

• However, good morphological conditions of fish depend on the quality and quantity of feed available, nature of farming systems, variations of water and soil parameters and other management schedules.

• In fish culture ponds where stocking densities exceed the availability of food, addition of supplemental feed is very significant because both natural and artificial food provides different types of nutrients to fish in adequate quantities.

• Deficiency of feed in ponds leads to stunted/diseased fish while excess diet pollutes the fish culture environments and thus enhance the cost of fish production.

• Furthermore, excess diet has led to various abnormalities in fin-fish such as vertebral deformities, scale loss, haemorrhages on skin and fin bases, exopthalinia, anorexia, depigmentation or changed in body color, muscle damage, anaemia, lethargy and reduced white blood cell count.

• Of course, these abnormalities also depend on the absence of several amino acids in the diet.

Types of Diet • Artificial feeds are generally considered as the dawn of a new era in

the strategy of fish culture industry.

• In order to maintain optimum fish health and growth, balanced diet

in adequate amounts should be supplied to fish culture ponds.

• Generally poor fish farmers use locally available diet for fish and

these diets are often poor in nutrient composition and not palatable

to fish although they contain appreciable amounts of proteins,

carbohydrates, fats and trace amounts of calories. •

CONT…• Generally two types of diets are used for fish culture: (1) pelleted diet

and (2) non-pelleted diet.

• Experiments have shown that the non-pelleted diet was conducive to survival and production of tilapia fish.

• In contrast, it has also been observed that there was significant benefit to feed conversion for catfish and carps if the food stuffs were pelleted.

• These indicate that selection of fish species is very important so far as the types of diets and their conversion efficiency are concerned.

• These are multi-micronutrient mineral fertilizers with essential balanced mixture of amino acids, macro and micro elements.

• They are mixed with artificial feed in suitable proportions.

• However, use of these nutrients is very important because

• (1) they are active stimulating agents for cell development

• (2) stimulate to increase the rate of photosynthesis,

• (3) enable for active participation of both nitrogen assimilation and fixation,

• (4) enhance production of phytoplankton, zooplankton and bottom organisms,

• (5) reduce annual production cost, and

• (6) help bone and muscle formation in fish.

CONT…• A wide variety of feed ingredients are used to prepare artificial

feeds. • The simplest fish feeds are prepared by using locally available

raw materials such as corn or rice bran and rice mill sweepings as sources of carbohydrates.

• These are mixed with animal proteins such as fish meal, trash fish and snail meat.

• However, commercial feed preparations and their formulations depend on culture system (such as semi-intensive, intensive, and traditional), species of fish and protein requirement.

• Fish feeds are marketed in various forms such as starter, grower, and finisher.

• Starter feeds are added on the first month of culture, finisher feeds on the last month, while the grower feeds in between finisher and starter feeds. Starter and finisher feeds have the crude protein contents of about 40 and 30 per cent, respectively.

Overfeeding • Although supply of high quality diet to fish ponds in

necessary, overfeeding may sometimes be harmful to fish and ecosystem as a whole.

• An experiment was conducted at Auburn University (USA) to determine precisely how much artificial food in earthen ponds would consume daily from small channel catfish fingerlings to harvest-size fish.

• Result which represents the maximum amount of supplemental feed that the catfish would accept, indicate that food decreased markedly as the growing season

progresses.