RUDN University biologist experimentally proved that adding pineapple peel powder to the diet of Nile tilapia accelerates its growth. This organic feed additive also increases their resistance to infections. An inexpensive supplement will be useful for fish farms. The study is published Fish and Shellfish Immunology.

Nile tilapia is one of the most popular farmed fish species. It grows quickly and can live in different climates. However, there is a high mortality rate of fish in overcrowded tanks or from infectious diseases. A RUDN University biologist has shown that pineapple peel helps strengthen the immunity of tilapia to infections.

"Crop waste can be an environmentally safe and cost-effective means of controlling fish infections. Feed additives are not medicines, but a diet enriched with them contributes to the development of safe microflora in the water on farms and in the intestines of fish. Harmless microbes limit the spread of dangerous pathogens. In addition, agricultural products contain a lot of nutrients. For example, pineapple peel, which accounts for up to 42% of the weight of each fruit, is rich in fiber, protein, and pectin, " Morteza Yousefi, PhD, Associate Professor of the Department of Veterinary Medicine of the RUDN University.

For the experiment, the RUDN University biologist developed five diet options for tilapia. All food systems were fairly high-calorie and balanced, but four of them additionally contained 5 to 40 grams of powder obtained from dried pineapple peel for each kilogram of feed. For eight weeks, five groups of 60 fry were fed according to one of the dietary programs.

During the study, all fish grew 6-7 times, but the largest weight gain (21 to 152 g) was observed in the group of fish that had 10 g/kg of pineapple peel in their feed. The same group was ahead in terms of immune system performance. Laboratory testing showed that the antibacterial enzyme lysozyme from their skin mucus is most active, and the expression level of genes responsible for the immune response increased. This resulted in the ability to resist real infections. Ten fish from each group were injected with a high content of streptococci S. agalactiae. All four pineapple-infused diets helped tilapia carry the infection more easily, but the most effective system again turned out to be 10 grams of powder per kilogram of feed. The survival rate after infection with streptococcus in this group was four times higher than in the group with no pineapple peel in a diet.

"Pineapple supplements have a positive effect on the growth and immunity of tilapia. Biologically active components of the plant, such as the bromelain, can play a role. It stimulates the activity of the immune system and promotes the functioning of the intestines. Other substances in pineapple can promote the growth of beneficial bacteria in the fish's body. But we also showed that the supplement should be included in the diet in small amounts. An excess of plant fiber restricts the growth of fish, and prolonged stimulation of the immune system by supplements leads, on the contrary, to suppression of immune responses," Morteza Yousefi, PhD, Associate Professor of the Department of Veterinary Medicine of the RUDN University.


Journal Link: Fish & Shellfish Immunology 114, 2021