Effect of low-fishmeal diets on some digestive physiological responses of juvenile and growing olive flounder (Paralichthys olivaceus) fed at an industrial-scale fish farm

Abstract This study examined the digestive physiological response of juvenile and growing olive flounder (Paralichthys olivaceus) fed low-fishmeal diets. P. olivaceus (mean initial weight: 7.86 g) were cultured in eight square concrete tanks (10 × 10 m) at a commercial fish farm and fed twice a day with four types of experimental feed (FM70 control, 70% fishmeal content; FM45, 45% fishmeal content; FM35A, 35% fishmeal content; FM35B, 35% fishmeal content + 7% insect meal + 1% insect oil) for 6 months. During feeding experiments, fish growth was observed at 2-month intervals, and digestive organs (stomach, intestine, and liver) were sampled. Organs were stained with hematoxylin/eosin and Alcian blue/periodic acid–Schiff’s solution for each intestinal tissue (pore intestine and pylori), cholecystokinin in the pylori, and pancreatic polypeptide expression in the liver. Trypsin, chymotrypsin, and lipase activities in the intestine were measured. No significant differences in any of the measured variables were observed among the control, FM45, FM35A, and FM35B treatments at any of the sampling intervals. These results suggest that a diet comprising 35% fishmeal with added insects will not affect the digestive physiology of P. olivaceus in commercial fish farming in Korea.