Effects of Three Dietary Growth Hormones on Growth Performance and Lysozyme Activity in Juvenile Olive Flounder, Paralichthys olivaceus

In this study, tests were conducted to investigate the effects of three dietary growth hormones, administered in various amounts, on the growth performance and lysozyme activity in juvenile olive flounder, Paralichthys olivaceus. Three dietary growth hormones, recombinant human growth hormone (rHGH), recombinant bovine somatotropin A (rBST A) and recombinant bovine somatotropin B (rBST B) were tested at three different supplemental levels (10, 20 or 40 mg/kg body weight per week) by a $3{\times}3$ factorial design and a complete randomized design in comparison to a control group. Fish were fed one of the ten experimental diets (control, $rHGH_{10}$, $rHGH_{20}$, $rHGH_{40}$, rBST $A_{10}$, rBST $A_{20}$, rBST $A_{40}$, rBST $B_{10}$, rBST $B_{20}$ and rBST $B_{40}$) for 6 weeks and afterward were analyzed for growth performance by measuring weight gain (WG), feed efficiency (FE), specific growth rate (SGR) and protein efficiency ratio (PER). Based on the factorial design analysis, fish fed rHGH diets demonstrated significantly higher growth performance than fish fed rBST A or rBST B diets. However there were no significant differences in WG, FE, SGR and PER between fish fed rBST A and rBST B diets. Neither hormone level nor the interaction between the different hormones and their various levels had a significant effect on WG, FE, SGR, PER, lysozyme activity or whole-body proximate composition. A complete randomized design analysis confirmed fish fed $rHGH_{10}$, $rHGH_{20}$, $rHGH_{40}$, rBST $A_{10}$, rBST $A_{20}$, rBST $A_{40}$, rBST $B_{20}$ and rBST $B_{40}$ diets for 6 weeks showed higher WG than fish fed the control diet (P<0.05). A higher FE was observed in fish fed $rHGH_{10}$, $rHGH_{20}$, $rHGH_{40}$, rBST $A_{20}$ and rBST $A_{40}$ diets in comparison to fish fed the control diet. Fish fed all graded rHGH, rBST A and rBST B supplemented diets showed a higher SGR than fish fed the control diet. Regarding PER, fish fed $rHGH_{10}$, $rHGH_{20}$, $rHGH_{40}$, rBST $A_{10}$, rBST $A_{20}$, rBST $A_{40}$ and rBST $B_{20}$ diets were higher than fish fed the control diet. Furthermore, the lysozyme activity of fish fed a diet of $rHGH_{20}$ was significantly higher than that of fish fed any other diet. The results measuring the growth and development of the fish clearly suggest the biopotency of dietary rHGH could be higher than those of both dietary rBST A and rBST B. Further implied is the probability that within the range of 10 to 40 mg/kg BW/week the dietary growth hormones could accelerate growth performance, and that 20 mg rHGH/kg BW/week could possibly enhance lysozyme activity in juvenile olive flounder, Paralichthys olivaceus.