Newswise — University biologist with colleagues from Iran discovered how to improve the health indicators of carp in fish farms. To do this, you need to mitigate the stress of the fish, which occurs due to too dense seating. Nanoselenium and garlic extract help with this. The results are published in the Journal of the World Aquaculture society.
To increase the profitability of fish farms, entrepreneurs increase the stocking density of fish in tanks. However, this practice is detrimental to the fish. Life in a densely populated tank disrupts the production of enzymes and other substances, and the health of the fish suffers from this. Biologist RUDN University with colleagues from Iran, using the example of grass carp (Ctenopharyngodon idella), found the optimal seating density. Also, biologists found a way to alleviate stress in fish with feed supplements of nanoselenium and garlic extract.
“Grass carp is actively grown in many countries. This is one of the first species of freshwater fish in the economy. Recently, intensive cultivation of grass carp in concrete ponds has been developing. In fish farms, profitability depends on the growth rate of the fish and the density of the fish in the tanks. Therefore, farmers choose high density to increase profitability. This is one of the most common environmental stress factors that can negatively affect the growth, survival, immunity and health of grass carp,” said Morteza Yousefi, Associate Professor of the Department of Veterinary Medicine at RUDN University.
Biologists studied more than a thousand individuals of carp. The fish were divided into 18 tanks with different densities. The most densely populated aquariums had 96 fish each, while the freest ones had only 24. The fish received various food additives. Half of the fish received 1 milligram of nanoselenium and 1 gram of garlic extract along with the usual food. The second group - twice as much as both additives.
After 60 days, PFUR biologists compared the growth parameters and health indicators of fish. The fish that grew the most grew when they received the double dose of supplements and lived in tanks with the lowest or average density. The worst performers were in fish that received a single dose of supplements and lived in the most densely populated aquariums. Regardless of density, the double-supplemented fish had lower levels of cortisol—the “stress hormone”—and glucose. They also increased the activity of amylase and lipase - enzymes that are involved in the digestion of starch and fats. Fish that lived in medium-sized tanks also had increased levels of protease and catalase, enzymes involved in protein digestion, wound healing, and antioxidant effects.
“We recommend higher levels of nanoselenium and garlic in the diet. This will help to suppress stress and improve the growth, digestive activity and antioxidant capacity of white carp. In addition, rearing fish in medium-density conditions is the best aquaculture practice,” said Morteza Yousefi, Associate Professor at the Department of Veterinary Medicine at RUDN University.
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