RUDN University Veterinarians: Shallots Will Improve Immunity and Growth of Trout

The increase in the fishing industry is forcing scientists and entrepreneurs to look for ways to optimize. It is also necessary to achieve maximum feed efficiency — so that the fish eat all the intended food and gain weight as quickly as possible. This task becomes more difficult when the fish live in cramped tanks and interfere with each other. Because of this, the fish are malnourished, their immunity is weakened. To prevent disease, industrialists use antibiotics—often incorrectly and unnecessarily. A RUDN University veterinarian 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. Growth and efficiency of assimilation of a forage decreases. The overuse 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. Therefore, for many years, researchers have been trying to find a suitable alternative to solve these problems,” Morteza Yousefi, Associate Professor of the Department of Veterinary Medicine of the RUDN University.

Shallots are known for their antimicrobial, anti-inflammatory, and antioxidant activity. Therefore, the authors chose it for study. Veterinarians separate fry of rainbow trout Oncorhynchus mykiss into five groups. Four groups, along with the usual food, received shallot supplements at different concentrations — 0.5, 1, 2 and 3%. Fish from the fifth group were fed only food. After 60 days of the experiment, veterinarians compared the degree of digestion of the feed, the rate of weight gain, as well as the biochemical parameters of the blood.

The fish that received the 2% shallot supplement had the best weight gain during the experiment, 36 grams versus 27 grams for the control group. The natural supplement also increased the concentration of globulin and albumin proteins, the antibacterial agent lysocycyme , and other substances responsible for the immune response. Improvements were observed at any concentration of the natural additive, however, according to the sum of the signs, the 2% additive proved to be the best.

“The diet enriched with shallots affected the blood biochemical parameters of trout fry. After the 60 day trial, we noticed a significant increase in the total amount of proteins, albumin and globulin in the blood. This indicates an improvement in immune parameters. 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” — Morteza Yousefi, Associate Professor of the Department of Veterinary Medicine of the RUDN University.

The results are published in the journal Aquaculture.