Newswise — RUDN University biologists with colleagues from Iran proved the effectiveness of the biofloc water purification system in aquaculture under conditions of high stocking density. The results are published in Aquaculture Nutrition.
In areas where water is scarce or land is expensive, fish farm owners are increasing the stocking density of fish in tanks. However, such conditions require a certain infrastructure for waste treatment. For this, there is a biofloc system. Biofloc performs two tasks at the same time - it purifies water from waste after feeding and serves as a source of nutritional supplements. The essence of the technology lies in the fact that small clots, “flocs”, from algae and bacteria, fungi and protozoa are placed in the tank. They absorb nitrogen, which remains after feeding the fish with food with a high content of protein and nitrogen.
“In order to increase the productivity and profitability of aquaculture, producers often use new culture methods with high density of fish in tanks. However, when combined with the high protein content of the diet, this leads to the formation of a large amount of waste that negatively affects natural aquatic ecosystems. Therefore, suitable methods are needed to conserve the environment and develop sustainable aquaculture,” Morteza Yousefi, Associate Professor of the Department of Veterinary Medicine, RUDN University.
Biologists placed fish in 15 different tanks with different densities - from 10 to 20 kilograms of fish per cubic meter. The fish lived in a biofloc system and were fed with a high protein content of 25% or 35%. Biologists in 60 days they placed the fish in extreme conditions - for a day they settled them in tanks with a density of 80 kilograms per cubic meter. Then biologists RUDN University compared the performance of fish with the control group - fish that lived in conditions of low stocking density and without the biofloc system.
The fish that grew best of all were those that lived in a tank with an average density (10 kg per cubic meter). However, the rate of feed assimilation in this group was lower than in the high-density tanks. Compared to the fish that lived without the biofloc system, the activity of some enzymes, amylase, lipase, protease, superoxide dismutase and glutathione peroxidase, significantly increased in other fish. After the test under extreme conditions, the fish that lived in the biofloc system showed lower levels of stress compared to the control group - they had lower levels of glucose and the stress hormone cortisol.
“The biofloc system in medium stocking tanks improves growth and stress resistance in fish. In addition, biofloc can compensate for the lack of protein in the diet of fish,” Morteza Yousefi, Associate Professor at the Department of Veterinary Medicine at RUDN University.
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