Shallots Improve the Growth of Trout

RUDN University biologist with colleagues from Iran, Italy and Thailand proved that it is possible to protect the immunity of rainbow trout and enhance its growth with the help of shallot extract. The results are published in Aquaculture.

The task of the fish industry is to achieve maximum feed efficiency so that the fish gain weight as quickly as possible. However, fish often live in cramped tanks and interfere with each other, their immunity is weakened. To prevent disease, industrialists use antibiotics—often incorrectly and unnecessarily. RUDN University Biologist with colleagues from Iran, Italy and Thailand showed that instead, you can use a harmless natural feed additive – shallot extract.

“From 5 to 15% of the feed is not eaten by the fish. Overcrowding increases injury rates, competition for space and food. This also increases the risk of immune suppression and susceptibility to disease. Feed is digested worse, growth decreases. Excessive and sometimes inappropriate use of antibiotics leads to the emergence of resistant bacterial strains, environmental pollution and the transfer of antibiotic residues to other species, including humans ”, said Morteza Yousefi, Associate Professor of the Department of Veterinary Medicine, RUDN University.

Shallots are known for their antimicrobial, anti-inflammatory, and antioxidant activity. Therefore, the authors chose it for study. Biologists divided fry of the rainbow trout Oncorhynchus mykiss into five groups. Four groups, along with the usual feed, received a supplement of shallots in different concentrations – 0.5%, 1%, 2% and 3%. Fish from the fifth group received simple food. After 60 days of the experiment, biologists compared the degree of digestion of food, the rate of weight gain, as well as the biochemical parameters of the blood.

Improvements were observed at any concentration of shallots, however, in terms of the sum of signs, the 2% supplement proved to be the best. Fish from this group gained weight better than others during the experiment – 36 grams versus 27 grams in the control group. The natural supplement also increased the concentration of the beneficial proteins globulin and albumin, the antibacterial agent lysocyzyme, and other substances responsible for the immune response.

“The diet enriched with shallots had a positive effect on the biochemical parameters of the blood of trout fry. After a 60 day trial, we noticed a significant increase in total albumin and globulin proteins in the blood. This indicates an improvement in immune characteristics. All indicators with remarkable consistency point to the usefulness of shallot extract. The optimal level was from 1 to 2%. However, in order to save money, a concentration of 1% of the extract is recommended for use in aquaculture,” said Morteza Yousefi, Associate Professor, Department of Veterinary Medicine, RUDN University.