Temperature and diet effect on the pepsin enzyme activities, digestive somatic index and relative gut length of Malabar blood snapper (Lutjanus malabaricus Bloch & Schneider, 1801)

An integrated experiment was performed on juvenile Malabar blood snapper (Lutjanus malabaricus) to investigate the effect of temperature and diet in their pepsin activities in relation with digestive somatic index (IDS) and relative gut length (RGL). One hundred twenty L. malabaricus juvenile (13-15 cm) were equally distributed among four exposed temperature treatments (22, 26, 30 and 34 °C) representing their seasonal range and to account for end of century predicted temperatures, and two diets as commercial pellet and natural shrimp. After 7 days of acclimation period fish were reared for 30 days in twenty four 400 l glass aquaria at a stocking density of 5 fish tank−1. All treatments were three replications. The result showed that, IDS and RGL gradually decreased with increasing temperature up to 30 °C and again increase at 34 °C. And the values were also higher in pellet feeding fish than shrimp feeding fish at all the temperatures. Alternatively, in pepsin activity, an increased activity was seen between 26 °C to 30 °C and this activity was significantly higher than the 22 °C and 34 °C (P < 0.05). In general, highest pepsin activity was observed among fish which fed on a natural shrimp diet reared at temperature 30 °C (5.47 ± 1.60 U mg protein−1), followed by those at 26, 34 and 22 °C (P < 0.05) at both diet however, no mortalities were observed. These results could be used as a basis for selecting a suitable diet for maximizing the growth and sustainable aquaculture coping with global warming.