Effects of ursodeoxycholic acid on growth and digestive enzyme activities of Japanese flounder Paralichthys olivaceus (Temminck & Schlegel)

Three experiments were conducted to elucidate the effects of ursodeoxycholic acid (UDCA) on growth performance and digestive enzyme activities of Japanese flounder Paralichthys olivaceus (Temminck & Schlegel) juveniles and larvae. In experiment 1 (growth study), duplicate groups of juveniles of about 7 g initial body weight were fed a UDCA diet (containing 0.025% UDCA) and a control diet (without UDCA) to apparent satiation twice a day for 6 weeks at 18-21 degreesC. In experiment 2 (enzyme study), triplicate groups of juveniles (7 g) were also fed the UDCA and control diets for 6 weeks under similar feeding and water management conditions to those for the growth study, digestive organs were collected every 2 weeks and their enzyme (alpha-amylase, lipase and protease) activities were assayed. In experiment 3, duplicate groups of 48-day-old larvae were fed two test microdiets (UDCA and control diets) for 30 min and assayed for enzyme activities 6, 12, 24, 36 and 48 h after a single feeding in the morning. The weight gain and feed conversion efficiency of the juveniles fed the UDCA diet in the growth study did not show any significant difference compared to juveniles fed the control diet. Total lipids, neutral lipids and triglycerides of the whole body and apparent body retention (%) of dietary lipids were notably higher (P < 0.05) in the UDCA group than the control. In the juveniles fed the UDCA diet, the activities of α-amylase and protease did not increase with holding time compared to the control diet, Lipase activity of the juveniles fed the UDCA diet was significantly higher than those fed the control diet. By contrast, the activities of α-amylase, lipase and protease of the larvae at 6, 12, 24, 36 and 48 h after final feeding did not show any difference between the dietary groups. These results suggest that UDCA may have an important role in lipid assimilation by increasing enzyme activity of the juvenile Japanese flounder, but there are few effects on growth performance of the juveniles and digestive enzyme activities of the larvae.