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Chapter 9. Diet Formulation and Manufacture

Chapter 9. Diet Formulation and Manufacture

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Hardy and Barrows

9.6. Ingredient and Diet Evaluation

9.6.1. Proximate Analysis

9.6.2. Nutrient Analysis

9.6.3. Chemical Tests

9.6.4. Chemical Score and Indispensable Amino Acid Index (IAAI)

9.6.5. Biological Evaluation

9.7. Glossary




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. Production goals

differ depending on the situation, and, in addition, production goals may

be, to some extent, mutually exclusive. For example, production goals may

be rapid, efficient weight gain and successful maturation and reproduction.

In fish farming, these production goals might have to be attained without

adding enriching nutrients to the aquatic environment, necessitating the use

of certain ingredients that increase the cost of feed or lower its efficiency.

This illustrates how feed formulation is an exercise in compromise. Feeds

used in research are designed with specific goals, such as the induction of

a vitamin deficiency or establishment of a minimum dietary requirement.

Such feeds are often comprised of highly refined ingredients containing

very low levels of the nutrient(s) being studied; regular feed ingredients

contain an array of essential nutrients. Naturally, such research feeds are

expensive and not used in production settings.

Diet formulation and manufacture are not independent activities, as mentioned above. When feeds are formulated, the pelleting characteristics of

mixtures are just as important as the nutritional content of the mixture. Production diets must be economical to manufacture, ship, store, and deliver

to the fish. Pellets must remain intact in water until fish consume them, not

only to ensure adequate intake of nutrients that might otherwise leach out

of the pellets, but also to minimize water pollution caused by disintegrating pellets. Thus, the way in which feed ingredients are chosen, prepared,

9. Diet Formulation and Manufacture


combined, and processed is influenced by many factors, and compromise

between the ideal and the practical is a necessity requiring a solid foundation

of knowledge and experience.

During the last several decades, enormous changes have occurred in the

formulation and preparation of efficient feeds for farmed fish, and these

changes have been driven primarily by the demands of the farming industry.

New methods of feed and ingredient production, changes in the availability and quality of ingredients used in feeds, the development of new feed

ingredients, the cultivation of new fish species, and advances in our knowledge of fish nutritional requirements have all influenced fish feed formulation and manufacture. Rising concerns about the effects of fish farming on

the aquatic environment, coupled with concerns about the dependence of

fish feeds on fish meal produced from fully utilized or overutilized wild fish

stocks, have also influenced fish feed formulation and manufacture. Further

expansion of aquaculture production can occur only if efforts to reduce pollution and to utilize sustainable feed ingredients are successful. Both of these

issues greatly affect feed formulation and manufacture. Industry-driven advances in fish feeds over the past decade have significantly improved the

efficiency of aquaculture, especially salmon farming. Over the next decade,

further improvements are necessary so that society accepts aquaculture as a

socially beneficial enterprise.

9.1.1. 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. These efforts were summarized by Embody

and Gordon (1924), who also 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


Hardy and Barrows

protein, 15–16% fat, 8% crude fiber, and 10% ash, expressed on a dry weight

basis. Wet Feed

During the 1920s and 1930s, salmon and trout were fed a variety of diet

formulations based on the availability of feed ingredients in the vicinity

of hatcheries and farms. Hatcheries and farms generally produced their

own feed on-site each day. The ingredients included salmon eggs; fresh,

canned, or frozen fish; oilseed meals; and brewer’s yeast; combined with

beef liver, spleen, horse meat, chicken eggs, and cottage cheese. Mixtures

such as one-third beef liver, one-third hog liver, and one-third salmon viscera were chopped and mixed at the hatchery, 2% salt was added to congeal the mixture, and it was delivered to the fish by a hatchery worker using

a spoon or ladle. This process was labor intensive, and since the mixtures

were wet and runny, the water quality was low. Feed for small fish was sometimes dropped through an air-blower fan to reduce the particle size. These

feeds contained about 60% moisture and had a texture similar to moist sawdust (Hastings and Dickie 1972). The feed cost per pound of fish ranged

from $0.032 to $0.57, and feed conversion ratios ranged from 2.0 to 8.0

(Donaldson and Foster 1937). Wet–Dry Feed Mixtures

In the 1940s, the demand for ingredients used in wet fish feeds increased

due to increased hatchery production and to competition from other users.

To extend the traditional ingredients, meat–meal mixtures were developed.

These diets were blends of slaughterhouse by-products and dry, commercially available feed ingredients. Cortland dry feed mixture No. 6, consisting of 24% each of dry skim milk, cottonseed meal, white fish meal, and

wheat middlings, with 4% salt added, was a typical dry feed (Phillips et al.

1940). This mixture was blended with an equal weight of beef liver and hog

spleen, water was added, and the mixed material was squeezed through a

potato ricer to feed small fish in troughs. Versions of the potato ricer were

adopted to use compressed air for large-scale applications to feed fish in

large production raceways (Pelnar 1947). Cortland dry feed mixture No. 10

was the same as No. 6, except that soybean meal replaced the cottonseed

meal. Feeding trials using brook trout at the Cortland hatchery in New York

indicated that growth rates equivalent to those obtained using a meat diet

were achieved using the meat–dry meal mixtures. The feed cost per unit of

production was reduced by about one-half (Tunison et al. 1941).

Meat–meal mixtures are still in use in many parts of the world. In northern

Europe, fish processing waste and fish silage combined with dry meal mixes

at 50:50 to 90:10 proportions constitute wet feeds for salmonids. The dry

9. Diet Formulation and Manufacture


mixes contain fish meal, cooked starch, vitamin and mineral premixes, fish

oil, and an alginate binder. These feeds are made at the fish-farming site and

fed within several days. In Japan, wet diets containing ground fish combined

with binders (90:10 ratio) are prepared for yellowtail and salmon. In Asia,

combinations of ground fresh fish, fish meal, and a dry meal containing

vitamins and binders are produced by small-scale farmers as an alternative

to purchasing ready-made feed. Generally, these types of wet diets support

excellent growth of fish. They are practical when the availability and cost of

fresh fish or fish processing waste and the cost of feed preparation warrant

their use. Semimoist Pelleted Feeds

During the late 1940s and 1950s, studies were conducted by the Oregon

Fish Commission and the Seafood Laboratory at Oregon State University

to develop a wet mixture–dry mixture combination salmon feed that would

not transmit disease to young salmon. At that time, fish tuberculosis, a disease caused by Microbacterium pisum, was a major problem in Pacific salmon

hatcheries. Although this was not a fatal disease of salmon fingerlings, on

their return to hatcheries as adults, infected fish could not be used as spawners because their gonads were not developed. The practice of feeding meat–

meal diets containing chopped salmon carcasses or salmon viscera was found

to be the primary way in which young salmon fingerlings were infected with

fish tuberculosis (Wood 1979). In other words, the disease was transmitted

from adult to offspring (vertical transmission) via the wet fish portion of the

diet. Disease transmission via the diet was eliminated by pasteurizing the wet

fish before it was used in the diet.

The next stage of development of semimoist feed, now known as the Oregon moist pellet (OMP), involved testing various ingredient combinations

to produce a mixture that could be easily formed into feed particles. By

reducing the proportions of pasteurized fish waste material and increasing

the dry meal, and by using ingredients in the dry mix that held the finished

product together, a semimoist (∼32% moisture) mixture of improved quality was developed.

The final refinement in semimoist feeds was the introduction of a practical method of forming pellets. Various methods to form feed particles

were evaluated. Potato ricers gave way to grease guns and, finally, to meat

grinders in which 50% of the holes in the die were plugged. The resulting “noodles” were chopped first by hand and then by a slow-turning fan

which made them into small particles. The drawbacks were that the particles were not of a uniform size and many fine and undersized particles

were created. The final step involved the use of commercial noodle machines with external cutting knives that chopped the noodles into the proper


Hardy and Barrows

Table 9.1

Oregon Moist Pellet Specifications

Percentage in diet


Herring meal (or anchovy

or hake meals up to 1/2

fish meals) except mash

Wheat germ meal

Cottonseed meal (48.5%)

Dried whey product or dried whey

Corn distillers’ dried solids

Sodium bentonite

Trace mineral premix

Vitamin premix

Choline chloride (70%)

Wet fish

Fish oil


Mash (OM-3)


OP-2 ( 18 -inch and

larger pellets)




























length for feeding. With this refinement, salmon diet preparation moved

from individual hatcheries to commercial plants where pellets were massproduced, quick-frozen, sacked, and shipped frozen. As the vitamin requirements of salmon were determined, vitamin premixes were developed which

ultimately resulted in the elimination of beef or fish liver from the diet of

young Pacific salmon.

The OMP formula continued to be modified and refined by the Oregon

Department of Fish and Wildlife, and eventually there were three OMP

formulations, a mash for fry, and two production formulations (Table 9.1).

In 1985, the State of Oregon closed its fish feed development program, and

further refinement of the open-formula OMP ceased. Several commercial

feed producers assumed responsibility for further evolution of the semimoist

feed, and today, semimoist feed is available from a single company in North

America. This feed is a closed-formula feed, meaning that its formulation is

the property of the feed company, but its basic formulation and manufacture

is similar to the OMP. Manufacturing processes for both moist and dry pellets

are described later in this chapter. Dry Pelleted Feed

During the period that semimoist feeds were being developed for salmon,

progress was being made in the development of dry compressed pellets for

9. Diet Formulation and Manufacture


trout. The first report on the successful use of dry pellets for trout rearing

appeared in 1956, building on decades of work at the Cortland laboratory.

Grassl (1956) found that trout hatchery production could be increased by

60% while feed costs were reduced by 40%. His formulations did not include

a supplemental vitamin premix, so he fed beef liver to the trout once every

3 weeks. The 10-cm fish reached a stocking size of 18 cm after 7 months of

feeding, less than half the growth rate expected at trout farms today.

The addition of a vitamin mixture to the dry formulation permitted the

successful rearing of trout to spawning and subsequent rearing of fry entirely

on manufactured pellets (Phillips et al. 1964). The formulations of Phillips

et al. (1964) for trout and Fowler and Burrows (1971) for fingerling Pacific

salmon provided the basis for the development of dry pellet formulations

produced throughout the world.

Open-formula diets for salmon and trout are diets for which the formulations are available to anyone, in contrast to closed-formula diets, which are

the proprietary property of feed companies. Open-formula diets are periodically updated and tested by the various governmental agencies that develop

them. Current specifications for severalof these diets are listed in Tables 9.2

Table 9.2

Open-Formula Diet Specifications for Abernathy Salmon Dietsa

Percentage in diet


Herring meal

Dried whey

Blood flour (or meal)

Wheat germ meal

Feather meal

Condensed fish solubles


Poultry by-product meal

Wheat middlings mill-run or shorts

Vitamin premix

Choline chloride (60%)


Trace mineral mixture

Lignon sulfonate pellet binder

Calcium propionate

Fish oil or soybean lecithin (max. 2%)


Year 2000 specifications.


S9 (92)


A2-2 (92)


A3-2 (92)













































Hardy and Barrows

Table 9.3

Open-Formula Diet Specifications for Salmonid Diets (MNR-98HS)a

Percentage in diet


Fish meal (70% CP)

Blood meal, animal (>85% CP)

Poultry by-product meal (65% CP)

Whey, dried (12% CP)

Alfalfa meal (15% CP)

Soybean meal (49% CP)

Brewer’s yeast (45% CP)

Corn gluten meal (60% CP)

Lysine hydrochloride

Vitamin premix

Mineral premix

Fish oil



































Ontario Ministry of Natural Resources (1998).

and 9.3. Dry, compressed pellets have several advantages over moist pellets.

First, dry pellets do not require frozen storage; room-temperature storage

is sufficient for at least 90 days after manufacture. Second, dry pellets can

be used in inexpensive, platform-type demand feeders (moist pellets do not

flow sufficiently to be used in most demand feeders). Third, dry pellets are

less expensive than moist pellets, especially when the cost of moist pellets is

expressed on a dry weight basis. Dry, compressed pellets also have several

disadvantages. First, some species of young salmon start feeding less readily

on dry feed than on moist feed, particularly in cold water (<7◦ C). Second,

dry, compressed pellets do not float in water, unlike extruded pellets. Third,

there is a limit to the amount of fat that can be included in the feed to be pelleted (<7%). However, by spraying on after pelleting (top-dressing), additional fat can be added to obtain levels of 16–20%.

Cooking extrusion is the most recent development in pelleted fish feed

manufacture. These pellets are formed by extrusion of a moist mixture (20–

24%) followed by drying to reduce the moisture content to 10% or less. Extruded pellets are used by the catfish, salmon, trout, and shrimp industries

and by many other sectors of aquaculture, particularly for fish farmed in

sea cages. The extrusion process expands starch in the feed mixture, which

lowers the pellet density. Extruded pellets can be made to float, sink slowly,

or sink rapidly in water, depending on the conditions of manufacture. Since

9. Diet Formulation and Manufacture


Table 9.4

Semipurified Diet Formulation for salmonids (H-440) and Oregon Test Diet (OTD)

and Guelph Test Diet for Trout


Vitamin-free casein








Fish oil (marine origin)

Vitamin E

Choline chloride

Mineral mix

Vitamin premix

Oil premix



Guelph (100)

























In vitamin premix

In vitamin premix



a Mineral mix contains the following (g/kg premix): calcium biphosphate, 135.7;

calcium lactate, 326.9; ferric citrate, 29.7; magnesium sulfate, 132; potassium phosphate

(dibasic), 239.8; sodium biphosphate, 87.2; sodium chloride, 43.5; A1C13 · 6H2 O, 0.15; KI,

0.15; CuC12 , 0.1; MnSO4 · H2 O, 0.8; CoCl2 · H2 O, 1.0; ZnSO4 · H2 O, 3.0.

b Vitamin premix contains the following (g/kg premix): α-Cellulose, 893; choline chloride, 56; inositol, 22; ascorbic acid, 11; niacin, 8.4; calcium-pantothenate, 5.6; riboflavin,

2.2; menadione, 0.45; pyridoxine hydrochloride, 0.56; thiamin hydrochloride, 0.56; folic

acid, 0.17; biotin, 0.06; vitamin B12 , 10 g.

c Oil premix contains the following (g/kg premix): corn oil, 664.7; cod liver oil, 331.9;

dl -α-tocopheryl acetate, 4.4.

d Mineral mix contains the following (g/kg premix): CaCO , 21; CaHPO · 2H O, 735;




K2 HPO4 , 81; K2 SO4 , 68; NaCl, 30.6; Na2 HPO4 · 6H2 O, 21.4; MnO, 25.0; FeC6 H5 O7 · 3H2 O,

5.58; MnCO3 , 4.18; 2CuCO2 · Cu(OH)2 , 0.34; ZnCO3 , 0.81; KI, 0.01; NaF, 0.02; CoCl2 , 0.2;

citric acid, 6.88.

e Vitamin premix contains the following (g/kg premix): thiamin hydrochloride, 3.2;

riboflavin, 7.2; niacinamide, 25.6; biotin, 0.08; calcium-pantothenate, 14.4; pyridoxine

hydrochloride, 2.4; folic acid, 0.96; menadione, 0.8; vitamin B12 , 2.67; inositol, 125; ascorbic

acid, 60.0; p-aminobenzoic acid, 20; vitamin D2 , 0.4; BHA, 0.75; Celite, 735.8.

they are dry, extruded pellets can be used in automatic and demand feeders. Extruded pellets are relatively porous and can soak up sprayed oil to

reach levels of over 35%, typical of feed for Atlantic salmon. The cost of

production is slightly higher for extruded pellets than for compressed pellets, but their advantages outweigh the additional cost in many aquaculture



Hardy and Barrows Semipurified Research Feeds

The adaptation of semipurified research diets for animals for use with

trout (McLaren et al. 1947; Wolf 1951) and subsequent refinement of these

diets for Pacific salmon (Halver 1957) and catfish (Dupree 1966) made

possible the determination of the essential nutrient requirements of many

species of fish. Semipurified diets contain highly refined ingredients, such

as casein, gelatin, egg white, and dextrin. These ingredients have very low

levels of vitamins and fairly low levels of the essential minerals required by

fish, so essential vitamins and minerals must be added to the diet to ensure

optimum growth and health (Table 9.4). In typical requirement studies on

fish, all nutrients are present in sufficient amounts except for the one being

studied. It is added at incremental amounts to test diets, and the response

of the fish is measured. In amino acid requirement studies, a mixture of

crystalline amino acids replaces a portion of the casein and gelatin, with the

amino acid being studied being added at incremental levels. Using this approach, the amino acid requirements of fish were first estimated (Dupree

and Halver 1970; Halver 1957). Other formulations for semipurified diets suitable for mineral studies, or other purposes, have been developed

[National Research Council (NRC) 1993]. Microdiets: Larval Feeds

Several other types of diets are used in aquaculture, usually for larval fish.

Examples are flaked and microencapsulated diets. Flaked diets, prepared

by drying a slurry on a steam-heated, double-drum dryer, have been used

for years as feed for ornamental fish in the aquarium industry. Micropulverized, flaked diets have been used experimentally as artificial food for larval

fish. Microencapsulation remains a promising technique to produce feed

for larval fish, due to the water stability of the capsule and the nutritional

completeness of the feed particles. This method of diet preparation has not

yet reached the practical stage, however.


Aims and Strategy of Fish Feed Production

Diet preparation is fundamentally a compromise between the ideal situation and practical considerations. It is not difficult to formulate a diet

that contains all of the known required nutrients at levels that meet or exceed the known requirements of the fish. However, when practical matters

are considered, the task becomes complicated. Practicalities such as the

ingredient price and availability, diet acceptability, pelletability of the formulation, pellet storage and handling requirements, and levels of antinutritional factors in certain ingredients are all of critical importance. The

9. Diet Formulation and Manufacture


ultimate goal is to produce a feed that supports maximum production at

the lowest possible cost. There are many possible formulations because aquaculture has many different aims, such as the production of food fish, fish

for stocking public or private waters, viable egg and fry production and the

propagation of ornamental fish. Each formulation is particularly suitable for

a specific application. Even when one species of fish is being reared with one

goal in mind, multiple formulations are used to fit various stages of growth

or production. For example, a “finishing diet” might be fed during the final

months before harvest to produce specific organoleptic properties, such as

flesh pigmentation in salmonids, and to support continued growth.

Some of these practical considerations are quantifiable and thus subject

to solution by mathematical means. Those that are not must be resolved

by the experience gained from preparing specific diets and determining

their qualities. Knowledge can also be gained by knowing the physical and

chemical properties of both individual feed ingredients and prepared feeds.


Feed Ingredients

Animal and fish feed ingredients are, for the most part, by-products of

food processing obtained when high-value food for humans is extracted

from a raw material. Once the high-value products have been removed, the

remaining material is further processed, usually by drying, to produce a

material that itself becomes an article of commerce. These ingredients are

normally available throughout the year, with prices depending on the forces

of supply and demand.

Not all feed ingredients are by-products; some are produced directly from

raw materials. Examples of these include anchovy meal, menhaden meal,

and ground whole grains. Practical and economic factors determine the fate

of these products. Feed ingredients for fish diets are chosen for a number of

reasons already mentioned, including the nutrient content, cost, availability,

and physical properties. Proximate composition is the primary means of

evaluating feed ingredients. In industry, proximate composition is expressed

on an as-is basis, which generally means a moisture content of 7–9%.

9.3.1. Feed Nomenclature

Feed ingredient nomenclature and classification began in Germany in

the early 19th century, when methods of determining chemical composition were developed. Feed ingredients were first classified on the basis of

nitrogen or digestible nutrient content. Nomenclature was originally based

on common names, but as the number of by-products from a single, raw


Hardy and Barrows

material increased, the use of common names became confusing. Harris

(1980) reported that a systematic investigation during the early development of today’s nomenclature system revealed that more than 20% of the

common names in use for feeds were simply different names for the same

product. Today’s system of nomenclature is called the International Feed

Vocabulary (IFV) and it is accepted worldwide (Harris 1963, 1980). It has

assigned a comprehensive name and number to each ingredient using descriptions from one or more of six categories. The categories are (1) origin,

which includes the scientific and common names for specific plants and animals, poultry, fish, cereals, grass, minerals, chemical products, and drugs or

other names for nonspecific materials; (2) part fed to animal as affected by

processing; (3) process(es) and treatment(s) to which the feed ingredient

was subjected; (4) stages of maturity and development; (5) cutting (for forage crops); and (6) grade. Using this system, herring meal is described as fish

herring, Clupea harengus, meal, mechanically extracted, International Feed

Number 5-02-000. Wheat mill run is described as wheat, Triticum aestivum,

flour by-product, less than 9.5% fiber, International Feed Number 4-05-205.

The last five numbers in the International Feed Number are assigned to each

ingredient name, the first number being a code for the feed class. There

are eight feed classes at present (Table 9.5). Over 18,000 feed ingredients

have been assigned numbers using this system (Harris 1980).

An organization called the International Network of Feed Information

Centers (INFIC) was formed to catalog information on feed ingredients and

disseminate this information throughout the world. One of the participating centers, the Feed Composition Data Bank, National Agriculture Library,

Beltsville, Maryland, provides the data used in feed composition tables,

such as those found in the United States–Canadian Tables of Feed Composition (NRC 1971) and the National Research Council’s series entitled

Table 9.5

Classes of Feed Ingredients









Dry forages and roughages

Pasture, range plants, and forages fed green

Silages (ensiled forages only)

Energy feeds

Less than 20% protein (dry basis)

Less than 18% crude fiber (dry basis)

Protein supplements: more than 20% protein (dry basis)

Mineral supplements

Vitamin supplements

Additives: antibiotics, coloring materials, flavors, hormones, and medications

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