An enkephalin analog stimulates growth of tilapia.

A synthetic enkephalin analog (Tyr-D-Trp-Ala-D-Phe-NH2) was administered to juvenile hybrid tilapia (Tilapia nilotica ×T. aurea) by immersing the fish for 15 minutes per week into one of two doses of the hormone for 8 weeks. Growth, food conversion efficiency, body weight, specific growth rate, food conversion efficiency and feed consumption were all significantly increased as a result of enkephalin treatment. The low dose (10µg/100 ml water) of enkephalin analog had a better stimulation effect than that of the high dose (100µg/100 ml water). Liver protein and protein/DNA ratio were higher in both treatment groups than in the control group. Tissue-body indices and muscle proximate composition were similar in the treatment and control groups. The growth stimulation in fish treated with the enkephalin analog was possibly mediated by an increase in growth hormone secretion.