Effects of Different Salinities on Growth, Feeding Performance and Plasma Cortisol Level in Hybrid TGGG (Tiger Grouper, Epinephelus fuscoguttatusx Giant Grouper, Epinephelus lanceolatus) Juveniles

The hybrid TGGG, tiger grouper Epinephelus fuscoguttatusx giant grouper, Epinephelus lanceolatus has a high resistance towards extreme conditions due to its genetic improvement. This study investigated the effects of different salinities on growth, feeding performance and plasma cortisol level in TGGG juveniles. The TGGG juveniles were acclimatized and subjected to 7 different water salinities at 5, 10, 15, 20, 25, 30 and 35 part per thousand (ppt) for 30 days. The survival rate, growth rate and feed conversion ratio (FCR) were calculated at 10-day intervals. The optimum salinity is 10 to 20 ppt based on higher growth performance in terms of the final weight (g= gram), average daily growth (ADG= g/f/d,gram/fish/day), and specific growth rate (SGR=%/d ,percentage/day) observed at 10 ppt (19.20±0.63 g, 0.32±0.01 g/f/d and 2.69±0.06%/d), 15 ppt (18.52±1.55 g, 0.31±0.04 g/f/d and 2.80±0.22%/d) and 20 ppt (18.17±1.04 g, 0.30±0.03 g/f/d and 2.74±0.23%/d). Besides, the optimum salinity was also determined based on the lower feed conversion ratio value at 10 ppt (1.24±0.04), 20 ppt (1.26±0.14) and 15 ppt (1.30±0.20). This study shows that high salinity at 35 ppt, (14.38±2.11 g, 0.19±0.02 g/f/d and 1.95±0.40%/d) and 30 ppt, (15.31±0.68 g, 0.21±0.02 g/f/d and 2.06±0.17%/d) leads to poor growth performance of TGGG juveniles. Plasma cortisol levels in 5 ppt (56.50 nmol/L), 15 ppt (19.31 nmol/L) and 35 ppt (33.54 nmol/L) were significantly higher compared to those in 10, 20, 25 and 30 ppt. On a broad scale, this study is very significant in providing useful information for the TGGG to increase mass production and promote economic growth.