Antinutrients in Fish Feed Ingredients

When fish feed is prepared without following proper procedures and dosages, fish feed is often damaged and poisoned by various types of anti-nutrients and toxins. Plants belong to the family Autotrophs; since they can produce their own food, green plants are called producers. They can synthesize many chemicals from nature, but animals cannot. All these elements in plants have a detrimental effect on the metabolic processes of animals. These plant ingredients used in the preparation of fish food are called antinutrients.

Anti-nutrients reduce the metabolism of fish and the activity of various glands and reduce the digestibility of food. These elements often cause poisoning in the body of the fish. Consumption of such foods reduces the rate of food change and at the same time consumes more energy in metabolic activities. As a result, the effectiveness of food is reduced. This reduces and hinders the growth of the fish, regulates various activities of the fish, disrupts the normal growth of the fish, and reduces food efficiency. Pancreatic hypertrophy, low blood glucose levels, hypoglycemia, and liver damage also cause a variety of diseases that can lead to fish death, which usually depending on the amount of food consumed, the species, the shape, the age, and the physiological condition.

Classification of Anti-nutrient Ingredients of Fish Feed

Antinutrients / growth inhibitors in plant foods are mainly divided into the following four types, viz.

  1. Protease inhibitors, Haemagglutinin / lectins
  2. Glycocides – Sepnin, Phytic acid, Glucocynolete
  3. Phenols – Gossypol, tannins
  4. Other- Anti-catalytic ingredients, anti-vitamin ingredients, toxic amino acids, food allergens etc.

The following is a description of the different types of anti-nutrients:

Protease Inhibitors

Protease inhibitor is a type of substance found in plants of the family Liguminoceae, such as soybeans, mustard, etc. Plants contain a variety of protease inhibitors that vary in molecular weight, structure, and function. Five types of protease inhibitors have been found in soybeans. Such protease inhibitors are associated with the enzymes chymotrypsin, trypsin, which interferes with its effectiveness. As a result, the digestibility of food decreases and the growth of fish decreases. When most protease inhibitors or their sources are properly heated, their effectiveness is reduced.


Like protease inhibitors, soybeans contain another type of nutrient, called hemagglutinin or lectin. It is a proteineous substance with a special addiction to sugar. Apart from oilseeds, such material is also found in tree roots and tubers. It reduces the absorption of nutrients in the intestines of the fish, prevents red blood cells from clotting, and slows down the growth of the fish by causing internal bleeding. As such nutrients are prone to heat, they can be deactivated through heat treatment.


Plants contain small amounts of cyanogen which is found as cyanogenetic glucoside. Cyanogen is found in relatively high amounts in some grains, root-producing plants, and fruit kernels. It is also found in some oil plants and is not toxic but hydrolysis itself, providing thiocynate, isocyanate, goitin and nitrite, and a type of enzyme (Mirosinase) is mainly responsible in the process of hydrolysis. All of them act as anti-thyroid ingredients to prevent the secretion of thyroid gland. Such enzymes can be inactivated by applying heat treatment. The cyanogen found in mustard oil can be soaked in water for 24 hours to stop its poisoning.


Gossipol is a polyphenotic pigment found in cotton plants such as the gossypium and other members of the family Malvaceae. About 15 gossip dyes have been found in cotton seeds, 8 of which have already been isolated. Such material has acidic properties. High doses of gossip reduce the activity of succinic dehydrogenase and cytochrome enzymes. It also reacts with iron to form an inert ferrous gossiplet complex. Symptoms of gossip poisoning include loss of appetite, weight loss, and weight gain. During food preparation, gossip reacts with proteineous food to reduce the quality of the meat and adversely affects the liver and kidneys of the fish. In order to prevent food poisoning in gossip, its harmful properties can be reduced by crushing cotton seeds and adding salt to the diet of fish with cotton seeds.


Mimosine is a type of abnormal amino acid found in plants of the family Leguminosae, especially epil-epil. Mimosine inhibits the production of thyroxine in the body and the growth of the organism. Epil-epil’s mimosine can be neutralized by soaking it in water and made suitable for use in fish feed.

Phytic Acid

Phytic acid is present in various types of oilseeds and grains used as fish feed such as cotton seed meal, mustard oil meal, soybean meal etc. Phytic acid is converted to insoluble phosphate by combining with various bipolar organic matter taken with food such as calcium, magnesium, zinc, phosphorus etc. As a result, the organic matter mentioned in the intestines of the fish cannot be properly absorbed. This causes malnutrition in fish. High levels of phytate cause zinc deficiency in fish. One study found that 0.5% phytic acid reduced fish growth by 10%. Phytic acid often combines with ingested food to reduce the digestibility of meat. As a result, the growth of fish is reduced. Most plant-based food products contain about 80% phosphorus, which causes fish poisoning in the form of phytates. The harmful effects of phytic acid can be reduced by crushing food and adding iron salts to food.

Cyclopropeonic Fatty Acid

Cyclopropeonic fatty acids are found in all types of cotton seeds. It is not possible to remove it through the oil extraction process. Its effects increase wound healing in the body, increase the level of glycogen and increase the level of soluble fatty acids in the liver. Such substances often destroy the liver by reducing the activity of enzymes in the liver. Such ingredients have to be inactivated by heat treatment before being used in food.

Erucic Acid

Erucic acid is a 22-carbon monounsaturated fatty acid. Such ingredients are found in rapeseed oil seeds. 20-55% of rapeseed oil is erucic acid. According to Parker and Hendricks, 3-6% of erucic acid causes problems in various parts of the fish, especially the skin, gills, kidneys and heart. Such ingredients have to be inactivated by heat treatment before being used in food.


Glucosinolate glycosides are anti-nutritional food ingredients. Various oilseeds, such as mustard, cauliflower, cabbage, etc., are used as the main ingredient in fish supplements. Such ingredients reduce the function of the thyroid gland. As a result the thyroid gland cannot absorb iodine. Fish growth is disrupted as the normal functioning of the thyroid gland is disrupted. Since such elements are heat prone and soluble in water, soaking or applying heat treatment reduces the amount and effectiveness of glucosinolate. The harmful effects of glucosinolate can be controlled by using a limited amount of mustard oil cake in the supplementary diet.


Pyrrolizidine alkaloids are a type of toxin found in a variety of plant species. 100 g / kg Pyrrolizidine alkaloids inhibit fish growth. Alkaloids of 200 g / kg cause necrosis, megalysis (mental disorder) and hepatic vein occlusion of the fish. As it is soluble in water, it can be inactivated by soaking it in water before use.


Fresh fish contains a type of enzyme that destroys thiamine, called thiaminase. Such enzymes are found more in freshwater fish than in marine fish. Thiaminase causes the destruction of thiamine vitamins. Therefore, the growth of fish decreases. Such ingredients must be inactivated by heat treatment before use in food.

Almost all the anti-nutrient or anti-growth ingredients present in various foods used to make fish supplements are sensitive to heat. The effectiveness of anti-aging or anti-growth products is lost if the food is half boiled or heat is applied before the supplement is prepared. As a result the quality of food increases. Harmful levels of these anti-growth products vary depending on the amount of their presence in the supplementary diet, fish species, age, and physiological conditions.

Table: Anti-nutrients found in plant foods

Feed ingredients



Protease inhibitor, hemagglutinin


Protease inhibitor, hemagglutinin


Protease insulation, phytic acid, invertase insulation

Sweet potatoes

Protease insulation, invertase insulation

Round potatoes

Protease inhibitor, hemagglutinin

Pea shoots

Protease inhibitors, hemagglutinin, phytic acid






Protease inhibitors, hemagglutinin, phytic acid, saponins

Mustard oil

Protease inhibitor, glucosinolate, antivitamin B1


Protease inhibitors, hemagglutinin, glucosinolate, phytic acid, saponins

Cotton seeds


Toxic and Accidental Substances in Fish Feed Ingredients 

The diversity and versatility of natural food and supplementary food sources of fish depends on the environment of a reservoir, the species of farmed fish, the variety of combinations and farming methods. Depending on the source of the natural food, the ingredients of the supplement and the method of preparation, the food ingredients can carry a variety of toxic, natural or external antioxidants. In fact some ingredients are produced in fish food which has a fatal effect on fish. Food is mainly contaminated by contaminants for three reasons, namely-

  • By absorbing contaminants from the environment and transferring them to the food cycle;
  • Due to high levels of toxic waste from industrial discharges into the habitat;
  • Also through the waste emitted from all the materials that are used in the production of various materials.

Notable anti-nutrients natural or foreign products found in fish food are-

  1. Solvent residue
  2. Mycotoxin or fungal toxin
  3. Fish toxin
  4. Algal toxin
  5. Insecticide residue
  6. Heavy metal
  7. Bacterial and viral toxin

Solvent Residue

Different types of solvents are used in the production of oil from oilseeds. Methylene chloride, ethylene, di-chloride, hexane, acetone and isopropyl alcohol are used as solvents in the production of oils from soybean, mustard, sesame, linseed and sunflower seeds. Some of these solvents used after oil production remain in the oil. If these oils left in the solvent are used in fish feed without refining, it disrupts the physiological process of the fish. As a result, the growth of fish is reduced and breeding is disrupted.

Mycotoxin or Fungal Toxin

Fungi grow on a variety of ingredients, such as cotton, soybeans, nuts, and other cereals, which are used as food supplements for fish. At high temperatures and high humidity, the fungus produces a powerful toxin called alphaitoxin. Common fungi that contaminate fish food are Aspergillus flavus, Penicillium sp.  These fungi are able to breed at a temperature of 550C and a minimum humidity of 75%. If the fish food is not stored in a good environment, it becomes contaminated by such fungi and produces various toxins. As a result of consuming food made from this poisonous food, the poisoning of the fish continues slowly. Such poisoning can result in lesions to the liver and other organs of the fish. As a result, the physiological process is severely disrupted and the growth of the fish is reduced. As a result, the fish died. In addition to alpha-toxins, many other types of mycotoxins are excreted in fish food, such as trichothesin toxins. Symptoms caused by such toxins include reduced food intake, reduced growth, and reduced hemoglobin levels in the blood.

Fish Toxin

Puffer fish and some other fish contain a kind of poisonous substance. In order to protect themselves from monster fish and other animals, the puffer fish and their relatives release fish poison. These toxins are harmful to humans, mammals and other fish. The lips, tongue, fingers and muscles of the people become numb due to the poisoning of the puffer fish. Poisoning often results in death. If puffer fish are used to make fish meal or fish silage, the fishmeal can cause toxic substances in the fish food.

Algal Toxin

Some green algae grow rapidly in water to form a green coating on the surface of the water. This is called algal bloom. In this way some algae release some toxins in the water. This poison is harmful to fish, humans and other animals. Many species of snails use these algae as food. As a result, algae toxins accumulate in the snails and the body cells are damaged by toxins. If the meat of this snail is fed directly to the fish or if it is used as a food supplement in the fish, it can cause fish poisoning. The algae that contain toxins are Mycosystis aeruginosa, Ganyaulax and Gyrodinium sp.

Insecticide Residue

Various types of pesticides are used in almost all crops to control insects for getting higher production. Some of these pesticides are absorbed by plant leaves, fruits, seeds, and even roots. The poisoning of these absorbed pesticides lasts for a certain period of time. Some pesticides are deposited in the body of the fish, namely- DDT, Die-Aldrin etc. Many times, pesticides containing leaves, vegetables or fruits are used as food for fish. The action of pesticides interferes with the sexual maturity of the fish, leads to infertility and neurological impairment and loss of appetite. If the intensity of poisoning is high, the fish dies. Many times these residues accumulate in the body of the fish and it is gradually transferred to the human body and disrupts the physiological process, i.e. DDT.

Heavy Metal

Mercury, copper, lead, cadmium, etc. are metals of high molecular weight. If these metals are found in sufficient quantities in any food and if the fish consumes these foods, the fish may die due to poisoning. Mercury and cadmium are stored in various marine fish. Fish meal made from marine fish is prone to infection by these metals.

Bacterial and Viral Toxin

Due to poor preparation techniques and quality, food ingredients are also infected by the virus and bacteria, which poses a risk to the health of fish and even humans. Pathogenic bacteria, especially Salmonella and viruses, represent serious health risks. If food can be prepared and stored in accordance with proper systematic and hygienic principles, then the food material can be kept away from bacterial and viral contamination.

Prevention of anti-nutrients or foreign substances in fish food

The following steps can be taken to get rid of contamination of anti-nutrients in fish feed-

  • Various oilseeds are the main ingredient in fish supplements. Before using it in the supplementary food, the residue of the solvent should be removed by purifying the oil cake.
  • Fish food and food preparation material should be stored in polythene bags at appropriate temperature. When making food, it is important to check if the food is infected by fungi.
  • Puffer fish or this class of fish cannot be used as raw material in making fishmeals.
  • Snails obtained from ponds containing poisonous algae cannot be used for fish feed.
  • In case of grains, appropriate amount of pesticides should be used. Only appropriate classified pesticides should be used in moderate doses in paddy fields or open water bodies. The use of DDT pesticides should be stopped completely.
  • If there is heavy metal in the food material to be used before making food, it should be ensured that its level is tolerable for fish.
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