brewmaster15
10-04-2004, 02:36 PM
This is a great article, and the author was very helpful by email when I inquired him as to nutrition and fish...
hth,
al
http://forum.simplydiscus.com//index.php?board=3;action=display;threadid=958
the article...
Hi all,
I have been trying to get a better handle on fish nutrition and came across an excellent reference. I have been in contact with the author and obtained permission to post it here. In the near future the entire web article will be accessible here as well.
Hope this is useful to you all,
al
An Introduction to
Nutrition and Feeding of Fish
Dominique P. Bureau and C.Young Cho
Fish Nutrition Research Laboratory
Dept. of Animal and Poultry Science
University of Guelph, Guelph, Ontario, N1G 2W1, Canada
email: dbureau@aps.uoguelph.ca
visit them at....http://www.uoguelph.ca/fishnutrition
In culturing fish in captivity, nothing is more important than sound nutrition and adequate feeding. If the feed is not consumed by the fish or if the fish are unable to utilize the feed because of some nutrient deficiency, then there will be no growth. An undernourished animal cannot maintain its health and be productive, regardless of the quality of its environment.
The production of nutritionally balanced diets for fish requires efforts in research, quality control, and biological evaluation. Faulty nutrition obviously impairs fish productivity and results in a deterioration of health until recognisable diseases ensues. The borderlines between reduced growth and diminished health, on the one hand, and overt disease, on the other, are very difficult to define. There is no doubt that as our knowledge advances, the nature of the departures from normality will be more easily explained and corrected. However, the problem of recognizing a deterioration of performance in its initial stages and taking corrective action will remain an essential part of the skill of the fish culturist.
1. Protein and Amino Acid Requirements of Fish
Protein
Protein is required in the diet to provide indispensable amino acids and nitrogen for synthesis of non-indispensable amino acids. Protein in body tissues incorporate about 23 amino acids and among these, 10 amino acids must be supplied in the diet since fish cannot synthesise them. Amino acids are need for maintenance, growth, reproduction and repletion of tissues. A large proportion of the amino acid consumed by a fish are catabolized for energy and fish are well-adapted to using an excess protein this way. Catabolism of protein leads to the release of ammonia.
Protein is the most important component of the diet of fish because protein intake generally determines growth (protein growth has, in general, priority), has a high cost per unit and high levels are required per unit of feeds.
First observations on fish protein and amino acid requirements came from studies on natural diet of different fish. Natural diet (plankton, invertebrates, fish) is generally rich in protein and has a good amino acid balance. All dietary proteins are not identical in their nutritive value. The nutritional value of a protein source is a function of its digestibility and amino acid makeup. A deficiency of indispensable amino acid creates poor utilization of dietary protein and hence growth retardation, poor live weight gain, and feed efficiency. In sever cases, deficiency reduces the ability to resist diseases and lowers the effectiveness of the immune response mechanism. For example, experiments have shown that tryptophan-deficient fish become scoliotic, showing curvature of the spine, and methionine deficiency produces lens cataracts. Salmonid diets generally contain 35-45% digestible protein (DP), or 40-50% crude protein. However, amino acids or protein must be supplied in relation to digestible energy (DE). The recommended ratio of protein to energy in the salmonid diet is 20-26 g DP/MJ DE (92-102 g protein per Mcal). Increasing these proportions increases ammonia excretion; the requirement for dissolved oxygen is also increased because the efficiency with which the energy is used is decreased.
Why do fish have such high requirements for protein? The main factors explain this phenomenon:
1) The protein requirement in terms of dietary concentration (% of diet) is high but the absolute requirement isn’t (g/kg body weight gain). This is due to the fact that fish have a lower absolute energy requirement than mammals. This results in similar g body weight gain/g protein ingested as mammal but better feed efficiency (gain:feed).
2) Protein (amino acids) is used as a major energy source. Some economy can be made here if other dietary fuel are present in adequate amounts, e.g. increasing the lipid (fat) content of diet can help reduce dietary protein (amino acid) catabolism and requirement. This is referred to as protein-sparing effect of lipids. Protein to useful energy ratio is the factor that should be considered, not % protein of the diet per se.
Indispensable amino acid requirements
10 Indispensable amino acids
Phenylalanine (Phe) Histidine (His) Isoleucine (Iso) Leucine (Leu)
Lysine (Lys) Methionine (Met) Tryptophan (Trp) Valine (Val)
Arginine (Arg) Threonine (Thr)
Table 1. Indispensable amino acid requirements of different species of teleost (g / 100 g protein)
Amino acids Salmonid Catfish Carp Tilapia Milkfish Sea Bream Sea Bass
Arg 4.2 4.3 4.4 4.1 5.6
His 1.6 1.5 2.4 1.7 2.0
Ile 2.0 2.6 3.0 3.1 4.0
Leu 3.6 3.5 4.7 3.4 5.1
Lys 4.8 5.0 6.0 4.6 4.0 5.0 4.8
Thr 2.0 2.1 4.2 3.8 4.9
Trp 0.6 0.5 0.8 1.0 0.6 0.6
Val 2.2 3.0 4.1 2.8 3.0
Met+Cys 2.4 2.3 3.5 3.2 4.8 4.0 4.4
Phe+Tyr 5.3 4.8 8.2 5.6 5.2
Table 2. Amino acid composition of common protein sources (g/ 100 g protein).
CP Met Lys Trp Thr Ile His Val Leu Arg Phe
(+Cys) (+Tyr)
Requirement 1.7 4.8 0.6 2.0 2.0 1.6 2.2 3.6 4.2 2.7
(2.4) (5.3)
Fish meal 68 3.1 7.9 1.1 4.0 4.2 8.8 7.9 7.1 8.3 3.6
Soybean meal 48 1.6 6.7 1.3 4.2 5.5 2.7 5.7 8.0 8.0 5.7
Corn gluten meal 60 3.2 1.7 0.5 3.3 3.8 2.0 4.5 15.7 3.2 6.3
Blood meal 85 1.2 6.3 1.2 4.5 0.9 3.6 6.1 12.2 2.8 6.0
Meat and bone meal 50 1.2 4.9 0.4 4.0 3.8 3.3 5.3 5.7 6.0 4.0
Poultry by-product meal 65 1.7 5.9 0.9 4.0 2.9 2.2 4.8 5.7 7.5 2.5
Feather meal 85 0.7 1.2 0.5 3.3 3.1 0.3 5.4 9.2 4.6 3.1
2. Lipids (Fats)
Lipids (fats) encompass a large variety of compounds. Lipids have many roles: energy supply, structure, precursors to many reactive substances, etc. In the diet or carcass of fish, lipids are most commonly found as triglycerides, phospholipids and, sometimes, wax esters. Triglycerides are composed of a glycerol molecule to which three fatty acids are attached. Phospholipids are also composed of a glycerol molecule but with only two fatty acids. Instead of a third fatty acid a phosphoric acid and another type of molecule (choline, inositol, etc.) are attached. Wax esters are made of a fatty acid and a long chain alcohol and are a common form of lipid storage in certain species zooplankton . The main role of triglycerides is in the storage of lipids (fatty acids). Phospholipids are responsible for the structure of cell membranes (lipid bi-layer). Fatty acids are the main active components of dietary lipids. Fish are unable to synthesize fatty acids with unsaturation in the n-3 or n-6 positions yet these types of fatty acids are essential for many functions. These two types of fatty acids are, therefore, essential for the animal and must be supplied in the diet.
Deficiency in essential fatty acid result in general, in reduction of growth and a number of deficiency signs, including depigmentation, fin erosion, cardiac myopathy, fatty infiltration of liver, and “shock syndrome” (loss of consciousness for a few seconds following an acute stress). Salmonids require about 0.5 to 1% long chain polyunsaturated n-3 fatty acids (EPA (20:5 n-3) and DHA (22:6 n-3)) in their diet. This amount is easily covered by ingredients of marine origins, such as fish meal and fish oil, which are always present in significant amounts in salmonid feeds.
3. Carbohydrates
Carbohydrates represent a very large variety of molecules. The carbohydrate most commonly found in fish feed is starch, a polymer of glucose. Salmonid and many other fish have a poor ability to utilize carbohydrates. Raw starch in grain and other plant products is generally poorly digested by fish. Cooking of the starch during pelleting or extrusion, however, greatly improves its digestibility for fish. However, even if the starch is digestible, fish only appear to be able to utilize a small amount effectively. Carbohydrates only represent a minor source of energy for fish. A certain amount of starch or other carbohydrates (e.g. lactose, hemicellulose) is, nevertheless, required to achieved proper physical characteristic of the feed.
4. Vitamins
The vitamins are generally defined as dietary essential organic compounds, required only in minute amounts, and which play a catalytic role and but no major structural role. So far, 4 fat-soluble and 11 water-soluble vitamins or vitamin-like compounds have been shown to be essential to fish. Requirement is generally measured in young fast growing fish. However, requirements may depend on the intake of other nutrients, size of the fish, and environmental stress. The recommended levels and the deficiency signs are summarized in Tables 3 and 4. Many symptoms of vitamin deficiency are non-specific. It is also tedious and expensive to analyze diets for vitamins. Therefore, diagnostic of vitamin deficiencies is often difficult. Nutritional disorders caused by vitamin deficiencies can impair utilization of other nutrients, impair the health of fish, and finally lead to disease or deformities. Nutritional deficiencies signs usually develop gradually, not spontaneously. However, the culturist may obtain clues of deficiency indirectly through low feed intake and poor live weight and feed efficiency.
Table 3. Vitamin requirement of salmonids.
Vitamin Requirement
Fat-soluble vitamins
Vitamin A, IU/kg 2,500
Vitamin D, IU/kg 2,400
Vitamin E, IU/kg 50
Vitamin K, mg/kg 1
Water-soluble vitamin, mg/kg
Riboflavin 4
Pantothenic acid 20
Niacin 10
Vitamin B12 0.01
Biotin 0.15
Folate 1.0
Thiamin 1
Vitamin B6 3
Vitamin C 50
Vitamin-like compounds, mg/kg
Choline 1,000
myo-Inositol 300
Table 4. Deficiency signs associated with various nutrients.
Deficiency Sign Nutrient
Anemia Folic Acid, Inositol, Niacin, Pyrodoxine, Rancid FatRiboflavin, Vitamin B12, Vitamin C, Vitamin EVitamin K
Anorexia Biotin, Folic Acid, Inositol, Niacin, Pantothenic AcidPyrodoxine, Riboflavin, Thiamin, Vitamin AVitamin B12, Vitamin C
Acites Vitamin A, Vitamin C, Vitamin E
Ataxia Pyrodoxine, Pantothenic acid, Riboflavin
Atrophy of Gills Pantothenic Acid
Atrophy of Muscle Biotin, Thiamin
Caclinosis : renal Magnesium
Cartilage abnormality Vitamin C, Tryptophan
Cataracts Methionine, Riboflavin, Thiamin, Zinc
Ceroid liver Rancid Fat, Vitamin E
Cloudy lens Methionine, Riboflavin, Zinc
Clubbed gills Pantothenic Acid
Clotting blood: slow Vitamin K
Colouration: dark skin Biotin, Folic Acid, Pyrodoxine Riboflavin
Convulsions Biotin, Pyrodoxine, Thiamin
Discolouration of skin Fatty Acids, Thiamin
Deformations: bone Phosphorous
Deformations: lens Vitamin A
Degeneration of gills Biotin
Dermatitis Pantothenic Acid
Diathesis, exudative Selenium
Distended stomach Inositol
Distended swimbladder Pantothenic Acid
Dystrophy, muscular Selenium, Vitamin E
Table 4. Continued
Deficiency Sign Nutrient
Edema Niacin, Pyrodoxine, Thiamin, Vitamin A, Vitamin E
Epicarditis Vitamin E
Equilibrium loss Pyrodoxine, Thiamin
Erosion of fin Fatty Acids, Riboflavin, Vitamin A, Zinc
Exophthalmos Pyrodoxine, Vitamin A, Vitamin C, Vitamin E
Exudated gills Pantothenic Acid
Fatty liver Biotin, Choline, Fatty Acids, Inositol, Vitamin E
Feed efficiency: poor Biotin, Calcium, Choline, Energy, Fat, Folic Acid,Inositol, Niacin, Protein, Riboflavin
Fragility: erythrocytes Biotin, Vitamin B12, Vitamin E
Fragility: fin Folic Acid
Fragmentation of erythrocytes Biotin, Vitamin B12, Vitamin E
Gasping, rapid Pyrodoxine
Goitre Iodine
Growth, poor Biotin, Calcium, Choline, Energy, Fat, Folic AcidInositol, Niacin, Pantothenic Acid, Protein, PyrodoxineRiboflavin, Thiamin, Vitamin A, Vitamin B12Vitamin C, Vitamin E
Hematocrit, reduced Iron, Vitamin C, Vitamin E
Hemoglobin, low Iron, Vitamin B12, Vitamin C
Hemorrhage: eye Riboflavin, Vitamin A
Hemorrhage: gill Vitamin C
Hemorrhage: kidney Choline, Vitamin A, Vitamin C
Hemorrhage: liver Vitamin C
Hemorrhage: skin Niacin, Pantothenic Acid, Riboflavin, Vitamin A, Vitamin C
Irritability Fatty Acids, Pyrodoxin, Thiamin
Table 4. Continued
Deficiency Sign Nutrient
Lesion: colon Biotin, Niacin
Lesion: eye Methionine, Riboflavin, Vitamin A, Vitamin C, Zinc
Lesion: skin Biotin, Inositol, Niacin, Pantothenic Acid
Lethargy Folic Acid, Niacin, Pantothenic acid, Thiamin
Lipoid liver Fatty Acids, Rancid fat
Lordosis Vitamin C
Myopathy, cardiac Essential Fatty Acids
Necrosis : liver Pantothenic Acid
Nerve disorder Pyrodoxine, Thiamin
Pale liver (glycogen accumulation) High Digestible Carbohydrate, Biotin
Photophobia Niacin, Riboflavin
Pinhead Starvation
Pigmentation, iris Riboflavin
Prostration Pantothenic Acid, Vitamin C
Rigor mortis, rapid Pyrodoxine
Scoliosis Phosphorus, Tryptophan, Vitamin C, Vitamin D
Shock syndrome Essential Fatty Acids
Slime, blue Biotin, Pyrodoxine
Spasm, muscle Niacin
Swimming, erratic Pyrodoxine
Swimming, upside down Pantothenic Acid
Tetany, white muscle Niacin, Vitamin D
Vascularization, cornea Riboflavin
5. Minerals
Inorganic elements (minerals) are required by fish for various functions in metabolism and osmoregulation. Fish obtain minerals from their diet but also from their environment. Many minerals are required in trace amounts and are present in sufficient quantity in the surrounding water for the fish to absorb through their gills. In freshwater, there is generally sufficient concentration of calcium, sodium, potassium and chloride for the fish to absorb and cover its requirements. The totality of the requirement for other minerals must, in general, be covered by the diet. Dietary minerals play many roles. There generally have a structural (e.g. bone formation) or catalytic (e.g. metalloenzyme) role. Minerals required by fish included calcium, phosphorus, sodium, potassium, magnesium, iron, copper, zinc, cobalt, selenium, iodine, and fluorine. The recommended levels of minerals in the diet are shown in Table 5. There are numerous deficiency signs and some are highlighted in Table 4. Reduced growth, feed efficiency and skeletal deformities is the most common signs of mineral deficiencies.
Table 5. Mineral requirement of salmonid fish in freshwater.
Mineral Requirement (mg/kg feed)*
Calcium (Ca) 10,000
Chlorine (Cl) 9,000
Potassium (K) 7,000
Sodium (Na) 6,000
Phosphorus (P) 6,000
Magnesium (Mg) 500
Iron (Fe) 60
Zinc (ZN) 30
Manganese (MN) 13
Copper (Cu) 3
Iodine (I) 1.1
Selenium (Se) 0.3
* Requirement in the absence of significant amounts of the specific mineral in the water.
6. Digestion
Digestive tract anatomy and physiology
Digestive system of fish is, in general, relatively simple compared to digestive system of birds and mammals but there are numerous similarities.
Structure Characteristics
Barbel taste buds
Mouth teeth, no chewing, taste buds
Pharynx pharyngeal teeth (calcified structures)
Oesophagus short, thick, taste buds, gizzard
Stomach present or absent, acid, enzymes, rate of digestion correlates with mass of food remaining in stomach, emptying is affected by temperature.
Anterior intestine secretive and absorptive epithelial cells, no villi but numerous folds present, microvilli present, enterocytes with brush border membrane
Pyloric caeca present in some case, variable # between species and individuals (rainbow trout 50-200 p.c.). Increase absorptive surface, number apparently shows weak correlation with digestibility and growth. Ratio intestine/fork length = 0.7, ratio intestine + p.c./fork length = 3.9
Pancreas Generally a diffuse tissue, except for eel, pike, flat fish
Hindgut Not really morphologically distinct from anterior intestine but cell type changes. Squamous epithelial cells, mucus production, highly vacuolated cells, absorption of macromolecules by pinocytosis (tissue reabsorb proteins (enzymes) for recycling).
Figure 1 Various digestive configurations
Reference : Smith, L.S. 1989. pp.331-421. In: Halver, J.E. (Ed.). Fish Nutrition. 2nd Edition. Academic Press, San Diego. 798p.
The Figure 1 show that anatomy of the gastrointestinal tract differs quite significantly between species, especially between species with difference feeding habits. Difference in total enzymes activity between species are not very pronounced for proteases and lipases but difference are rather significant for carbohydrases.
Estimates of apparent digestibility for salmonids
Table 6 presents the apparent digestibility coefficients for commonly used ingredients in salmonid feeds as measured by Cho et al. (1982). Fish have different digestive capabilities compared to terrestrial animals, and many feedstuffs, particularly cereal grains and their by?products which contain high levels of starch and fiber, are very poorly digested by carnivorous fish. The apparent digestibility of good quality protein by fish is very high. However, several factors can affect the digestibility of protein. The type of drying technique used during processing is a very important factors. A good demonstration of this is seen in blood meal. The protein digestibility of flame-dried blood meal is very low whereas the digestibility of spray-dried blood meal is very high. The same phenomenon can occur with fish meal.
Table 6. Apparent digestibility coefficients of ingredients measured with rainbow trout.
Apparent digestibility coefficients (%)
Ingredients Dry Matter Crude Protein Lipid Energy
Alfalfa meal 39 87 71 43
Blood meal
ring-dried 87 85 - 86
spray-dried 91 96 - 92
flame-dried 55 16 - 50
Brewer’s dried yeast 76 91 - 77
Corn yellow 23 95 - 39
Corn gluten feed 23 92 29
Corn gluten meal 80 96 - 83
Corn distiller dried soluble 46 85 71 51
Feather meal 77 77 - 77
Fish meal, herring 85 92 97 91
Meat and bone meal 70 85 - 80
Poultry by-products meal 76 89 - 82
Rapeseed meal 35 77 - 45
Soybean, full-fat, cook. 78 96 94 85
Soybean meal, dehulled 74 96 - 75
Wheat middlings 35 92 - 46
Whey, dehydrated 97 96 - 94
Fish protein concentrate 90 95 - 94
Soy protein concentrate 77 97 - 84
7. Feed Formulation and Manufacturing
Diet formulation
Diet formulation and preparation are the process of combining feed ingredients to form a mixture that will meet the specific goals of production. It is often a compromise between the ideal formula and practical considerations. The primary objectives are to produce a mixture that (is) :
Nutritionally balanced (to support maintenance, growth, reproduction, health)
Economical Palatable
Water stable Minimizes waste output & effect on water quality
Produces desirable final product (attractive & safe)
Practical considerations :
Ingredients price and availability Anti-nutritional factors
Pelletability of mixture Storage and handling requirements
Table 7. Composition of the grower formulae used by the OMNR Fish Culture Stations over the past 10 years.
Formulae
Ingredients MNR89G MNR91H MNR95HG MNR98HG
%
Fish meal, herring, 68% CP 20 35 18 18
Blood meal, spray-dried, 80% CP 9 9 - -
Corn gluten meal, 60% CP 17 15 49 37.6
Soybean meal, 48% CP 12 14 - -
Poultry meal, 68% CP - - - 13
Brewer’s dried yeast, 45% CP - - 6 -
Wheat middlings, 17% CP 20 - - -
Whey, 12% CP 8 10 11 9
Vitamin premix 0.5 0.5 1 0.5
Mineral premix 0.5 0.5 1 0.5
L-Lysine - - - 1.4
Fish oil 13 16 14 20
Digestible Composition
Digestible protein, % 37 44 44 42
Digestible energy, MJ/kg 17 20 20 21
DP/DE, g/MJ 22 22 22 20
Ingredient Quality
The first consideration for formulation and production of successful diets is the quality of the feed ingredients. Diets produced with poor quality raw materials and under adverse processing conditions have inferior nutritive value and adverse effects on fish health. Quality criteria for the ingredients must be respected to insure that the final product is of consistent quality and that deleterious effects are avoided. The chemical composition (nutrient, energy, antinutrients, contaminants) of the ingredient obviously plays a determinant role the quality. However, biological aspects, such as digestibility and utilization of nutrients are most important and often overlooked.
The loss of indigestible matter from the diet as feces is the primary reason for variation in the nutritional value of feed ingredients. Measurement of digestibility provides, in general, a good indication of the availability of energy and nutrients, thus providing a rational basis upon which diets can be formulated to meet specific standards of available nutrient levels. Several factors can affect the digestibility of protein or specific amino acids. The type of drying techniques used during processing, the composition of the protein fraction are the factors which have a determinant effect on the digestibility of protein of a feed ingredients.
Fishery by-products:
There are various qualities of fish meals on the market, relating to the original raw fish quality, level of ash in the meals, and the type of processing techniques used. The most important factor is the freshness of the product. Fish must be processed as soon as possible after capture. Ageing and spoilage decrease the nutritive value and also lead to the contamination with potential toxic compounds, such as histamine, cadaverine, and agmatine. The second most important factor is the type of raw material used (whole fish or by-products). By-products, such as those generated by the filleting industry (sometime referred to as white fish meal) have higher level of ash and lower level of protein than whole fish meals. High level of ash generally affects digestibility of dry matter and results in high waste outputs, and can also produce mineral imbalances (e.g. Zn deficiency).
The type of fish used is not necessarily a determinant factor in the quality of the products. At equal freshness and if the same processing technique is used, whole capelin, anchovy, herring, menhaden meals will support similar growth. During processing, the drying treatment is a key factor. Flame-dried products are less digestible and produce lower performances.
Table 8. Quality Standards of Fish Meal Required for Salmonid Diets.
Compound Levels
Crude protein (%N x 6.25) > 68%
Lipid < 10%
Ash, total < 13%
Salt (NaCl) < 3%
Moisture < 10%
Ammonia-N < 0.2%
Antioxidant (sprayed liquid form) < 200 PPM
ADC dry matter > 85%
ADC crude protein > 90%
Particle size < 0.25 mm
Steam processed
Animal by-products
Animal protein by-products can very useful complementary protein sources in fish diets. It is important to use highly digestible products with limited ash content. High ash content ingredients are generally more polluting and the ash dilute useful nutrient. It is especially important when buying these products to deal with suppliers who consistently provide high quality products. Apparent digestibility of animal by-product is relatively high (Table 6) and they have been used at significant levels in practical diet with success. For blood meal, the type of drying is of primary importance. Spray-drying produce the best results.
Plant protein by-products :
There are several plant proteins and grain by-products that are used on a regular basis in fish diet formula. Certain plant protein products have a good nutritional value (high in digestible protein, good amino acid profile) and are economical at the same time. Other products improve the physical characteristics of the pellets. The incorporation of certain products must be limited for various reasons, such as their content in starch and fibre, the presence of antinutritional or undesirable factors and their acceptability (palatability).
Many plant products contain antinutritional factors. Most plant protein ingredients are heat treated during processing, which greatly reduce the level of several antinutritional factors, such as soybean trypsin inhibitors. Excess heat, however, generally decreases the nutritional quality of plant protein products by destroying amino acids.
Fish diets formulated with high levels of certain plant protein ingredients appear to be nutritionally adequate but not very acceptable to certain fish species. For example, diets containing high levels of soybean meal are poorly accepted by chinook salmon and other salmonids. Recent experimental evidences suggest that soyasaponins may be a factor affecting performance of salmonids fed soybean meal.
Corn gluten meal is a plant protein ingredients known to be highly palatable for salmonids. Studies with rainbow trout and Atlantic salmon show that it complements soybean meal very well nutritionally. Recent results from our laboratory showed that corn gluten meal or combination of corn gluten meal and soybean meal can replace most of the fish meal without any effect on performance of the fish. Nonetheless, the incorporation of corn gluten meal must be limited in food fish production feeds due to its high concentration in xanthophylls which can produce undesirable pigmentation of the skin and flesh and may compete with expensive synthetic pigment added in the feed. However, recent evidences from our laboratory do not support this hypothesis.
Fats and Oils
Fish oil is the main source of lipid in salmonid diet. Marine fish oils are, in general, excellent sources of long chain n-3 PUFA (EPA & DHA), fatty acids required by salmonid. Other types of oils and fats can be used in salmonid diets. Vegetable (canola, soya, safflower, etc.) oils and animal fats (tallow, lard, poultry fat) can also be used at certain levels in feeds without effect on growth performance and health of the fish.
Rancidity problems: Marine oils are rich in polyunsaturated fatty acids and are susceptible to rancidity. In all circumstances rancid oil must be avoided in the preparation of fish feeds. Rancid fat has deleterious effect on some of the nutrients present in fish feed and health of the fish. fatty liver disease is usually seen in fish fed rancid fat. Histologically, the main feature is the extreme infiltration of hepatocytes by lipids. Peroxide (PV), thiobarbituric acid (TBA) and anisidine (AV) values are in general parameters used to determine the degree of rancidity of lipid sources. Acceptable quality parameters for fish oil as suggested by Cho et al. (1983) are presented in Table 9. There is no unequivocal technique to measure rancidity and there is still doubts about the reliability of PV, AV and TBA value. High PV, AV or TBA suggest problems of lipid deterioration but are not always indicative of harmful rancidity. The easiest way to determine if a feed is rancid may be its smell. Feed with a rancid smell must not be fed. It is preferable to discard such feeds instead of jeopardising the health of the fish by feeding them.
Table 9. Quality Standards of Oils and Lipid in Final Product Required for Salmonid Diets
Parameters Levels
Oils
Iodine value Report value
Peroxide value < 5 meq/kg
Anisidine value < 10
Pesticides, total < 0.4 PPM
PCB's < 0.6 PPM
Nitrogen < 1%
Moisture < 1%
Antioxidant (liquid form)* < 500 PPM
No vitamin fortification
Clean odour
Lipid in final product
Iodine value > 135
n-3 polyunsaturated fatty acids > 15%
Diet preparation and manufacturing
The are several forms of fish feed, including wet, moist, and steam-pelleted and extruded dry pellets. However, two basic types of formulated feed are generally used in intensive fish culture: dry and semi-moist diets. The diets are similar, the basic difference being that semi-moist pellets contain a larger proportion of raw fish and by-products which contribute a higher moisture level to the final product. Moist feeds have some merit in coastal regions where fresh raw fish and by-products are regularly available and economical. It is also possible that the physical characteristics of moist pellets are more palatable to some fish species. However, there is no evidence that such feeds are nutritionally superior to dry feeds. Moist feed may contain pathogens since the feed ingredients are only submitted to moderate heat treatment (pasteurization). In contrast to moist diets, dry feed are heat-treated and generally free from pathogens. They are also easier to transport and store. The bulk purchase and storage of quality dry ingredients is possible and ensures a continuous supply of quality feed. The dry ingredients on the commodity market are more quality defined than raw fisheries products and can be supplied regularly. Hence it is possible to formulate dry feeds more precisely with the available knowledge of fish nutrition. Most nutrient in dry feeds are stable are room temperature and therefore dry feeds can be stored safely without freezing for periods which depend on storage conditions (approx. 3 months in a cool, shady, and well-ventilated location).
Widely used dry feeds today may divide into three types: (1) steam-pelleted feed; (2) partially extruded, slow-sinking pellets, and (3) expanded and floating pellets. Feeding dry pellets either by hand or with automatic feeders is much simpler than that of moist feeds. The problem of acceptability of dry feeds by some fish species can usually be solved by better feeding techniques and fish culture management. Otherwise, fry which have difficulty in accepting dry feeds can be started with semi-moist feed and gradually shifted over to dry feed within 3-5 weeks.
A formulated dry fish feed must be pelleted and/or crumbled so as to be durable and water stable. Formulated feeds must also have desirable physical and textural characteristics, and be of the correct sizes to be readily acceptable by different sizes of fish. Disintegrated and uneaten feed pollutes the water and creates stresses from low oxygen and high nitrogen and organic wastes, with serious effects on growth and health. Some of the important factors in manufacturing a durable, dry fish feed without fines are (1) physical properties of the ingredients, (2) particle size of ingredients, (3) conditioning time and temperature in the pellet mill, (4) quality of steam supply, (5) compression pressure through the die, and (6) efficiency of sifting/grading and fat-spraying equipment. Many of the dietary problems experienced in fish culture in the past have been related to the physical quality of the pellets and granules, which was in turn related to poor quality ingredients, inadequate manufacturing processes, and negligent practices. Unfortunately for fish feed, the manufacturing process is of crucial importance. Having to transfer dietary nutrients into the fish through the water medium presents problems which are unknown in other animal-feeding practices. Therefore, all newly opened bags should be checked for the presence of excess fines, undersized granules, durability, foreign particles, too little or too much oil, mildew, and other evidence of poor quality. Any bag or batch of feed judged to be questionable and any with a detectable “rancid” smell should not be fed. All questionable feed should be immediately reported to a qualified nutritionist and returned to the manufacturer for replacement.
Table 10. Recommended particle size for salmonid diets
Feed Feed size Feeding per day Fish size (g)
Broodstock Pellets
7 Pt. 6.4 mm x 7 mm long 0.5 - 2 > 200
Grower Pellets
6 Pt. 6.4 mm x 6 mm long 1 - 2 > 200
5 Pt. 4.8 mm x 5 mm long 2 < 200
4 Pt. 3.4 mm x 4 mm long 3 100
3 Pt. 2.4 mm x 3 mm long 3 50
Grower Granules
3 Gr. 3 mm 3 < 50
2 Gr. 2 mm 4 20
Starter Granules
1.5 Gr. 1.5 mm 4 < 10
1 Gr. 1 mm 5 3
0.5 Gr. 0.5 mm 6 - 8 1
8. Feeding Systems
Feeding systems may be defined as all feeding standards and practices employed to deliver nutritionally balanced and adequate amount of diets to animals, so maintaining normal health and reproduction together with efficient growth and/or work performance. Until now the feeding of fish has been based mostly on folkloric practices while the main preoccupation has been to develop “magic” diet formulae. Many “hypes” such as mega-fish meal and mega-vitamin C diets have come and gone, and we are now in the age of the “Norwegian Fish Doughnut” (>36% fat diet)! Whichever diet one decides to feed, the amount fed to achieve optimum or maximum gain is the ultimate measure of one’s productivity in terms of biological gain, economical benefit and/or environmental sustainability.
Scientific approaches have been used in the feeding of land animals for over a century. The first feeding standard for farm animals was proposed by Grouven in 1859, and included the total quantities of protein, carbohydrate and ether extract (fat) found in feeds, as determined by chemical analysis. In 1864, E. Wolf published the first feeding standard based on the digestible nutrients in feeds.
Empirical feeding charts for salmonids at different water temperatures were published by Deuel and his colleagues and were likely intended for use with meat-meal mixture diets widely in use at that time. Since then several methods of estimating daily feed allowance have been reported. Unfortunately all methods have been based on the body length increase or live weight gain, and dry weight of feed and feed conversion, rather than on biologically available energy and nutrient contents in feed in relation with protein and energy retention in the body. These methods are no longer suitable for today’s energy- and nutrient-dense diets, especially in the light of the large amount of information available on the energy metabolism of salmonids.
Many problems are encountered when feeding fish, much more so than with feeding domestic animals. First, delivery of feed to fish in a water medium requires particular physical properties of feed together with special feeding techniques. It is not possible in the literal sense to feed fish on an "ad libitum" basis, like it is done with most farm animals. The nearest alternative is to feed to "near-satiety" with very careful observation over a pre-determined number of feedings per day; however, this can be very difficult and subjective. Feeding fish continues to be an "art" and the fish culturist, not the fish, determines "satiety" as well as when and how often fish are fed. The amount of feed not consumed by the fish can not be recovered and, therefore, feed given to them must be assumed eaten for inventory and feed efficiency calculations. This can cause appreciable errors in feed evaluation as well as in productivity and waste output calculations. Meal-feeding the fish pre-allocated amounts by hand or mechanical device based on theoretical energy requirement may be the only logical choice. Uneaten feed represents an economical loss and becomes 100% solid and suspended wastes! Meal-feeding a pre-allocated amount of feed calculated based on the theoretical energy requirement of the animal may not represent a restricted feeding regime as suggested by some since the amount of feed calculated is based on the amount of energy required by the animal to express its full growth potential.
There are few scientific studies, based on nutrition and husbandry, on feeding standards and practices; however, there are many duplications and "desktop" modifications of old feeding charts with little or no experimental basis. Since the mid-1980's, development of high fat diets has led to most rations being very energy-dense, but feeding charts have changed little to reflect these changes in diet composition. Most feeding charts available today tend to over-estimate feed requirements and this overfeeding has led to poor feed efficiencies under most husbandry conditions, and this represent a significant, yet avoidable, waste of resources for aquaculture operations. In addition, it may results in self-pollution which in turn may affect the sustainability of aquaculture operations. Recent governmental regulations imposing feed quota, feed efficiency guidelines and/or stringent waste output limit may somewhat ease the problem. Sophisticated feed management systems, such as underwater video camera or feed trapping devices, have been developed to determine fish satiation or the extent of feed wastage and are promoted by many as a solution to overfeeding. However, regardless of the feeding system or method used, accurate growth and feed requirement models are needed in order to forecast growth and objectively determine biologically achievable feed efficiency (based on feed composition, fish growth, composition of the growth). These estimates can be used as yardsticks to adjust feeding practices or equipment and to compare results obtained.
The development of scientific feeding systems is one of the most important and urgent subjects of fish nutrition and husbandry because, without this development, nutrient dense and expensive feeds are partially wasted. Sufficient data on nutritional energetics are now available to allow reasonably accurate feeding standards to be computed for different aquaculture conditions. Presented here is a summarized review of the basis of a nutritional energetic approach to estimating feed requirement and waste output of fish culture operation as well as the development of the Fish-PrFEQ computer program. Results obtained from a field station are presented and provide a framework to examine the type of information that can be derived from bioenergetic models and generate a feed requirement scenario for the next production year.
PRODUCTION RECORDS
Evaluating and/or predicting growth performance of a fish culture operation or a stock of fish firstly requires production records of past performance. These records may become databases for calculating growth coefficients, temperature profiles during growth period and feed intake and efficiency for various seasons etc. One such production records for a lot of rainbow trout from a field station is shown in Table 11. A lot of 100 000 fish was reared over a 14-month (410 days) production cycle between May, 1995 and June, 1996. Cumulated live weight gain (fish production) was 72 tonnes with feed consumption of 60 tonnes which gave an overall feed efficiency (gain/feed) of 1.19 (ranged between 1.11 – 1.22). Water temperature ranged from 0.5°C in winter to 21°C in summer which is typical of most lakes in Ontario. In spite of the wide fluctuation in water temperature, the thermal-unit growth coefficients (TGC) was fairly stable ranging between 0.177 – 0.204. Total mortality was around 9% over 410 days.
From the production record (Table 11) one can extrapolates an overall growth coefficient of 0.191 and this coefficient can be used for the growth prediction of next production cycle with assumption of similar husbandry conditions and fish stock are used. Total feed requirement and weekly or monthly feeding standards can be computed on the basis of this growth predictions plus the quality of feed purchased.
Table 11. - Fish production records from a field station
Month-End Days No. Fish Weight (g/fish) TGC Total Biomass (kg) Total Feed (kg) Gain/Feed Temp (°C) Flow Rate (L/min)
1995
Initial 100000 10.00
May 15 98900 12.05 0.184 1191.75 167 1.22 5.00 2500
Jun 30 95000 36.45 0.189 3462.75 2000 1.18 18.00 6000
Jul 31 95000 89.84 0.197 8534.80 4300 1.18 19.00 10000
Aug 31 94500 177.43 0.175 16767.14 7200 1.15 21.00 16000
Sep 30 94000 296.26 0.184 27848.44 9500 1.18 19.00 20000
Oct 31 93500 396.06 0.199 37031.61 7800 1.20 11.00 25000
Nov 30 93200 451.03 0.197 42036.00 4300 1.19 5.50 25000
Dec 31 93000 455.85 0.176 42394.05 400 1.12 0.50 25000
Jan 31 92000 460.77 0.178 42390.84 400 1.14 0.50 25000
Feb 28 91500 465.23 0.177 42568.55 370 1.11 0.50 25000
Mar 31 91200 470.39 0.184 42899.57 420 1.12 0.50 25000
Apr 30 91000 475.54 0.188 43274.14 420 1.12 0.50 25000
May 31 91000 534.65 0.200 48653.15 4500 1.20 5.00 30000
Jun 30 90800 783.37 0.204 71130.00 18500 1.22 18.00 50000
TOTAL 410days 0.191 60277kg feed 1.19 13.5 mill. m3water used
Procedures for the Estimation of Feed Requirement and Waste Output
Using production records as a starting point, feed requirements and waste output can scientifically be estimated based on the following three concepts:
1) Prediction of growth and nutrient and energy gains
2) Estimation of excretory and feed waste outputs
3) Quantitation of energy and nutrient needs
1) Prediction Of Growth And Nutrient And Energy Gains:
Accurate prediction of growth potential of a fish stock under given husbandry condition is an inevitable prerequisite to the estimation of energy or feed requirement (e.g. weekly ration). The formula most commonly used for fish growth rate expression is instantaneous growth rate known as "specific growth rate (SGR)" which is based on the natural logarithm of body weight:
SGR = (ln FBW - ln IBW) / D. (1)
where
FBW is final body weight (g)
IBW is initial body weight (g)
D = number of days
SGR has been widely used by most biologists to describe growth rate of fish. However, the exponent of natural logarithm underestimates the weight gain between the IBW and the FBW used in the calculation and it also grossly overestimates predicted body weight at weights greater than FBW used. Furthermore the SGR is dependent on the IBW, making meaningless comparisons of growth rates among different groups unless IBW are similar.
A more accurate and useful coefficient for fish growth prediction in relation to water temperature is based on the exponent 1/3 power of body weight. Such a cubic coefficient has been applied both to mammals and to fish. The following modified formulae were applied to many nutritional experiments:
Thermal-unit Growth Coefficient (TGC)
= [FBW1/3 - IBW1/3] / S[T x D] x 100 (2)
Predicted Final Body Weight
= [IBW1/3 + S (TGC/100 x T x D)]3 (3)
where:
T is water temperature (*C)
(NOTE: 1/3 exponent must contain at least 4 decimals (e.g. 0.3333) to maintain good accuracy)
This model equation has been shown by experiments in our laboratory and several field stations to represent very faithfully the actual growth curves of rainbow trout, lake trout, brown trout, chinook salmon and Atlantic salmon over a wide range of temperatures. Extensive test data were also presented by Iwama and Tautz (1981). An example of the relationship among growth, water temperature and TGC is shown in Figure 11. Growth of some salmonid stocks used for our exp
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