Pineapple skin diet shown to boost growth and immune system of tilapia
Commercial pineapple skin waste typically ends up being composted, or even just dumped in landfills. According to new research, however, a feed additive made from powdered skins has been shown to help farmed tilapia fish avoid infections, plus it reportedly boosts their growth.
According to scientists at Russia's RUDN University, pineapple skins are rich in fiber (particularly pectin) and protein. With these qualities in mind, a team led by Assoc. Prof. Morteza Yousefi started by drying out pineapple skins, then grinding them into a powder which was added to commercial tilapia feed.
For eight weeks, five groups of 60 Nile tilapia fry were raised on that feed, although the amount of pineapple skin powder in the feed varied from group to group. Four of the groups received feed with a skin content of either five, 10, 20 or 40 grams per kilogram, while the fifth group served as a control, receiving feed with no added skin powder.
Although all of the fish grew throughout the two-month period, the greatest weight gain was observed in the group that consumed feed with an added 10 g/kg of pineapple skin powder. The tilapia in that batch gained between 21 and 152 grams (0.7 to 5.4 oz) each. Additionally, it was found that fish in the 10-gram group showed the greatest activity of the antibacterial enzyme lysozyme in their skin mucus, plus the expression level of genes responsible for their immune response was the most increased.
When 10 tilapia from each group were injected with streptococci S. agalactiae bacteria, all of the fish that consumed the skin powder were better able to withstand the infection, with the 10-gram fish doing the best. The survival rate for fish from that group was four times higher than that of the control group.
"Biologically active components of the [pineapple] plant, such as the bromelain, can play a role," explains Yousefi. "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."
The research is described in a paper that was recently published in the journal Fish and Shellfish Immunology.