Tilapia is a popular fish around the world, and now, researchers from Russia’s RUDN University have discovered a way to make the fish more resilient─using a feed ingredient that would otherwise end up in landfills.

The researchers spent eight weeks raising five groups of 60 Nile tilapia fry, experimenting with a feed that includes powdered pineapple skin. Four groups received varying concentrations of the pineapple skin (five, 10, 20, or 40 grams per kilogram), and one served as a control group. The scientists found that the tilapia which consumed feed containing 10 g/kg of powdered pineapple skin grew the fastest. Plus, this group also had the highest concentration of the antibacterial enzyme lysozyme in their skin mucus as well as the highest expression level of genes responsible for their immune response.

When injected with streptococci S. agalactiae bacteria, fish that were fed pineapple skin were better able to fight off infection.

“Biologically active components of the [pineapple] plant, such as the bromelain, can play a role,” said study lead Morteza 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.”

Pineapple skin is a waste byproduct of fruit processing operations, so repurposing it into a fish food additive both helps the fish and reduces food waste. However, the researchers note that since the 10g/kg group was the strongest, the additive should be used in moderation.

Source study: Fish and Shellfish Immunology – Impacts of pineapple peel powder on growth performance, innate immunity, disease resistance, and relative immune gene expression of Nile tilapia, Oreochromis niloticus