Veterinarians developed a way to protect carp from the harmful effects of ammonia

Veterinarians from RUDN University have developed a way to increase the resistance of carp, the most common fish in fish farms, to the harmful effects of ammonia, which is found in almost all water bodies. The researchers found that the amino acid arginine can be helpful if added to fish food. The article was published in the journal Aquaculture.

One of the main problems of fish farms is the pollution of water with ammonia (NH3). The compound gets into water bodies because of human activities: from wastewater treatment plants, with drains from livestock farms and fields where nitrogen fertilisers are used. Ammonia reduces the ability of haemoglobin to bind oxygen, acts on the nervous system, affects red blood cells, and can lead to fish death.

Director of the Department of Veterinary Medicine of RUDN University Yuri Vatnikov and his colleagues have developed a way to use food additives to increase the resistance to ammonia in common carp, a species that is of great economic importance: fish farms sell about four million tons of carp per year, according to the UN Food Organisation (FAO).

The veterinarians conducted two experiments in which they examined the effect of arginine, an amino acid that stimulates the release of growth hormone.

In the first experiment, 600 carp were distributed over 4 tanks and kept there for 10 days, so that the fish adapts to new conditions. After that, for two weeks the fish in each tank was fed following one of four feeding options: with the addition of arginine in the proportion of 0.25%, 0.5%, or 1% by weight of the food, and without the addition of arginine (control group). Then the fish from each tank was distributed over 15 30-liter aquariums, 10 animals each. Then an ammonia solution was being added to the water for 3 hours, concentrations of 0.7, 0.8, 0.9, 1.1, and 1.3 mg / l. And finally, the water was vented and the condition of the fish assessed.

In the second experiment, 60 carp were distributed over 6 aquariums. After two weeks of acclimatisation, for the next 14 days half of the specimens were fed with food to which no arginine was added, and another half was on a diet that included 0.5% arginine. Then, ammonia solution concentration of 0.7 mg / l was added to all tanks. After three hours of exposure to ammonia, the researchers took the blood of carp for analysis.

In the first experiment, the fish exposed to an aqueous solution concentration of 0.7 mg / l ammonia survived regardless of the type of diet. An increase in the dose of ammonia led to the death of some specimens, and with the maximum ammonia concentration of 1.3 mg / l, all fish died. In the group where arginine supplementation was 0.25%, mortality was 5-10% lower. With an increase in the dose of arginine to 0.5%, mortality decreased even more significantly, by about 35%.

The purpose of the second experiment was to study fish blood samples. Exposure to ammonia reduces the content of amino acids, which play an important role in the formation of urea, in particular, the amino acids ornithine and citrulline. The addition of arginine increased the production of amino acids, which enhanced the processing of ammonia into urea. Thus, excess ammonia was excreted from the body.

The problem of the toxic effects of ammonia is of great importance in aquaculture. Fish farmers are interested in ways to suppress the side effects of ammonia. The new study offers a working method based on dietary manipulations: addition of just 0.5% arginine to the carp' food reduces the fish mortality from exposure to ammonia by 35%. The additive activates detoxification, i.e. turning ammonia into urea, and suppresses oxidative stress caused by exposure to ammonia.