May 22, 2008

Citrus peel shows promise in fish feed

South Korean scientists are exploring the use of citrus peel from fruit processors as fish feed.

The research, led by Dr Seon-Heui Cha of the University's Faculty of Applied Marine Science, is based on the fact that compounds in citrus peel contain polymethoxylated flavones (PMFs), antioxidants that belong to a group of plant chemicals called flavonoids.

Dr Cha and his team made two kinds of functional fermented fishmeal (FFM) from dead fish found in aquaculture farms and citrus peel. One contained citrus peel, the other contained rice bran but no citrus peel.

Statistical trials showed that the FFM containing the citrus peel showed strong antioxidant ctivities against the DPPH free radical (about 95 percent) and hydrogen peroxide (around 80 percent) in a concentration of 4 mg/ml.  It also exhibited enhanced protection to flounder leukocyte against H2O2-mediated DNA damage.

Two experimental diets were formulated for the Japanese flatfish. One pellet was a normal raw fish moisture pellet, the other diet was the same but contained 7 percent FFM with citrus peel.

The feeds with FFM were found to have enhanced the growth and significantly decreased the mortality of the fish.

Fish fed FFM also had significantly higher lysozyme activity and NBT reduction, according to the team's findings.

Overall, FFM with citrus peel improved the immune response of cultured olive flounder, Dr Cha said.