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
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
• 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,
• 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.
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
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
• 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.
• 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
• 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 meatpacking, 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 byproducts meal is similar to that of whole-egg protein,
which is the standard by which protein quality is
• 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 spraydrying 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
• 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 byproduct 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 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
• 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
• 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
• 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
• 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
• 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 byproducts of brewing that are sometimes used in fish feed
• 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%
• Brewer’s grains have limited use in fish diets because of their
bulk and the difficulty in grinding them to a consistent particle
• 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
• 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
Energy Sources
Carbohydrates (Starch) from Grains
• Basal feeds, or energy feeds, are low-protein, high-energy feed
• 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
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
• Thus, after the nutrient requirements have been met, basal
feeds can be used to fill out the energy needs in animal feed
• 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
• 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
• 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
• 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
• 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 of fat and oil can be prevented by adding
• 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
• Thus, additional vitamin and mineral premixes are
added to feeds to ensure adequate intake of these
• 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
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
• .
• 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
• 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
• 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
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 βcarotene 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
• 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.
Nonspecific immune stimulants, (neutriceuticals)
• It physically attach to pathogens and thus render them
• 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.
• 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
• 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
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 growthpromoting 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
• 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 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 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
• Thus, antioxidant concentrations fall during the initiation phase,
and once they are used up, oxidation reactions proceed very
• 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.
• 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 highmoisture 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 finfish 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.
• 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.
• A wide variety of feed ingredients are used to prepare artificial
• 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,
• 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