Fish Feed Additives
Additives are those materials which are used as small quantity in the fish feed during feed preparation to increase feed attraction, palatable to the species under culture system and to prevent disease, and microbial activities and to enhance the horse power efficiency of feed.
Additives is being used in animal feedstuff including-
Synthetic Amino Acids
The major synthetic amino acids available for supplementation are L-lysine and DL-methionine. These are used as chemoattractents as well as to supplements deficiencies in a compounded feed. It elicits feeding responses. Generally, extractive compounds in muscles of mollusks and crustaceans are principal flavor attractants. These attractants are a mix of chemicals nitrogenous compounds including free amino acids, low molecular weight peptides, nucleaotides and related compounds and organic bases.
Individuals or premixes of vitamins are commercially available. Vitamins are used to supplement for deficiencies in the compounded feeds. It also provide additional protection against lipid oxidant, enhancing its storage life.
Table: Vitamin requirements for growing fish
Requirements (units/kg diet)
4000-20000 IU1000-2000 IU
1600-2400 IU500 IU
25 mg50-100 mg
4 mg6 mg
5-6 mg10 mg
0.0.53 mg/l0.073 mg
240 mg50 mg
Binders are substances used in diets to improve their palatability, enhance their durability, preserve their physical form during storage and to preserve the water stability. It also reduces feed wastage and helps to produce a relatively robust pellet, helps to minimize nutrients losses.
The binders may be broadly grouped into two:
- Natural materials (sea and land plants extracts and animal extracts)
- Artificial binders (synthetic chemicals or synthetic derivatives of natural chemicals)
Table: Common Natural Binders
Sea plant extracts
Land plant extracts
* Most commonly used: inclusion rate 1-4% except for starches where the inclusion rate is (10-20%)
Common Artificial Feed Binders
Artificial binders commonly used in the preparation of fish/shrimp feed include-
- Bentonites(1-2% as sodium or calcium bentonite)
- Lignosulphonates(1-4% from pulp industry)
- Hemicelluloses (1-2% from spray dried wood pulp filtrate)
- Carboxymethycellulose (0.5-2.0%)
Starches are found from many plant feedstuff such as cassava, palm, rice flour, and maize flour, are the most effective, easily available and cheapest binders for pelleted feeds. These feedstuff can be added to the pellete premix upto 10%.
On the basis of the water stability, binders are grouped into:
Short term water stability binders: Lignosulphonates, hemicelluloses and Carboxymethycelluloses
Long term water stability binders: Starches, alginates, seaweed extracts, plants gum, Chitosun and gelatine
Polymethylcarbamide (Basfin) is an important binders which binds carbohydrate and protein. This binders are unpalatable and is not approved by the United State Food and drug Administration(USFDA).
Urea formaldehyde/calcium sulphate mixture(Maxibond) is an USFDA approved binder and has no. recorded disadvantages
Both Basfin and Maxi-bond are added at 0.5% or less to the feeds, are activated by steam during pelleting.
Binders for Moist/semi-moist Feeds:
Alginates are usually used for moist and semi moist feeds which form gels or high viscous solution. Occasionally solution of calcium ions, vit, calcium sulphate are required to promote gel formation. Common salt (Nacl) is also used at 10% of the feed successfully to bind raw rash fish and moist feed combination.
To control or delay the onset of rancidity many antioxidants are usually used. These may be vitamin premixes. Rancidity makes feeds unpalatable and generates toxic chemicals. Naturally occurring antioxidants are vitamin E or synthetic chemicals. In feed making industries, available commercial antioxidants, are BHT(Butylated Hydoxytoluene), BHA(Butylated Hydoxyanisole) and ethoxyquine. BHA and BHT are approved for using in human foods, are sometimes used in animal feeds. Ethoxyquin is approved only for use in animal feeds. Maximum levels of synthetic antioxidants permitted by the USDA is 0.2% of the fat content for BHA and BHT and 150 mg/kg feed for ethoxyquin.
To prevent the rate of deterioration particularly by attacking from fungal, various substances are used to feeds. These particular components are known as preservatives. Among the preservatives, most important components are sodium or potassium salts of propionic, benzoic or sorbic acid.
Use of antibiotics is totally discouraged in fish. This is because residues of antibiotics may remain in the fish/shrimp body, which may eventually be hazardous for human health. However, if becomes externally necessary to use antibiotics to combat disease, optimum dose and with drawl period should be maintained. Routine use of antibiotics in feeds is recommended, as it leads to resistant strains of bacteria.
Various natural and synthetic hormones are used in fish feeds including growth hormone, thyroid hormones, insulin and various sex steroids. Synthetic androgens enhance growth and improve feed conversion rate in some species (eg. Salmonids). Some warm water fishes such as channel catfish negatively responses to the feeding of androgens. Anabolic steroids are used in the culture of certain species, not with a view to enhances growth but with a view to obtaining populations of a single sex, generally all male populations of certain species. This is achieved by giving anabolic steroids in the diets during the fry stages.
Antimicrobial agents are used to prevent fungal contamination. It can be added directly to the unpelleted feed and the commonest substances recommended are shown in the following Table:
Table: Antimicrobial agents used in feeds
Benzoic acids, sodium benzoate
Propionic acid, calcium/sodium propionate
None, 0.02 %
Methyl or propyl paraban
Na or K sulphate, bisulphate and metabisulphate
None, use 1%
For a feed to be acceptable to a fish it must fulfill a number of criteria including the correct appearance and texture (shape, size, degree of hardness/softness, buoyancy) and taste. Feeding stimulants can be selected or added to feeds with the aim of stimulating the feeding responses.
Some feedstuff exhibit natural feeding stimulant properties. These include fish meal, fish oils, squid meal, shrimp meal and waste, betaine and some yeast hydolysates. Some synthetic chemical derivatives have also been shown to act as stimulants and these include mixtures of L-amino acids, betaine some nucleotide bases include mussels, squid, shrimp-waste and fish products. Feeding stimulants are increasingly used for commercial application in aquaculture feeds.