Olive Boosts the Immunity of Rainbow trout

Rainbow trout (Oncorhynchus mykiss) is one of the most popular species in fish farms that accounts for 2% of the total fish industry volume in the world. To meet the growing demand, fish farmers have to increase the production volume and speed. However, this has a negative effect on the health of the fish. Infections are quick to occur and spread in overpopulated aquafarms, and after some time of treatment, antibiotic-resistant bacterial strains emerge and suppress the immunity of the fish. The fish dies and the costs of the farms go up. A biologist from RUDN University suggested replacing medicinal drugs with plant supplements that don’t have these negative side effects.

“There is a tendency to replace chemical drugs with green alternatives such as plant and algae extracts that can improve fish health without causing any harm. Natural immunity boosters can increase the capacity of fish farms, make the fish healthier, and reduce the risks of financial losses. That is why we decided to study the potential influence of olive waste on the growth of fish and its immune system,” said Morteza Yousefi, Ph.D., an assistant professor at the Department of Veterinary Medicine, RUDN University.

Dr. Yousefi added olive waste to the feed of rainbow trout to test its ability to improve the immunity of the fish, as well as their antioxidant system (i.e. a body’s function of preventing excessive cell oxidation). In the course of a six-day-long experiment, the fish were divided into three groups. The first group received 5 grams of olive waste per 1 kg of feed, the second one got 2.5 grams, and the third was a control group and was fed without any supplements.

A week into the experiment, Dr. Yousefi found some positive developments in groups 1 and 2: the levels of an antibacterial enzyme in their blood serum and mucous membranes went up, and the concentration of immunoglobulin in their skin mucus increased. Moreover, the fish from groups 1 and 2 ingested their feed better and grew faster. The activity of antioxidant enzymes was the highest in the group that received 2.5 grams of olive waste per 1 kg of feed.

“One can conclude that adding 2.5 grams of olive waste per 1 kg of feed facilitates the growth of rainbow trout and improves its antioxidant and immune response, as well as the response of its skin mucus. We recommend considering olive waste as a feed supplement for rainbow trout. In the future, we plan to continue our studies and analyze the effect of the olive waste supplement on infectious, bacterial, and viral diseases,” added Dr. Yousefi.

An article about the work was published in the Fish and Shellfish Immunology journal.