Raw Fish-based Moist Pellet and Extruded Pellet on Growth, Levels and Expression of GH/IGF Axis, Intestinal Enzyme Activity and Gastrointestinal Morphology of Olive Flounder (Paralichthys olivaceus): An Actual Field Study

A six-month feeding trial was conducted to investigate the effect of moist pellet (MP) and commercial extruded pellet (EP) on the somatic growth, level and expression of GH/IGF axis, intestinal enzyme activity and gastrointestinal morphology of olive flounder (Paralichthys olivaceus) reared under actual farm conditions. MP was a raw fish-based diet composed of mackerel and cutlass fish while EP diet was a locally-produced commercial feed. Weight growth rate showed no significant difference (P>0.05), although EP-fed fish had a better somatic yield. Feed conversion ratio was better and condition factor has significantly improved when given EP diet (P<0.05). Plasma level of growth hormone and insulin-like growth factor 1 was comparably similar between diets, but EP-fed olive flounder had a higher hepatic IGF-1 expression (P<0.05). The activity of trypsin, chymotrypsin and lipase were insignificantly influenced by diets (P>0.05). The overall gastrointestinal morphology was in similitude regardless of diets, but EP- fed fish had a longer intestinal villi length and goblet cell count in the pyloric caeca (P<0.05). These dietary induced differences are discussed to have partly promoted better growth in EP diet. The findings suggest an equivalent, or better utilization of EP diet in the actual farm operation.