Dietary bovine lactoferrin enhances tolerance to high temperature stress in Japanese flounder Paralichthys olivaceus

Bovine lactoferrin (LF) was orally administrated to Japanese flounder juveniles to investigate the effect of LF on tolerance to high temperature stress. Four different concentrations of LF (0, 400, 1000 and 2000 mg LF/kg diet) were supplemented in test diets and fed to juveniles (mean body weight = 11.8 g) at 26.7 °C. After feeding for 30 days, lethal time to 50% mortality (LT50) after being exposed to 34.0 °C seawater (lethal stress test) and the levels of heat shock protein 70 family (HSP70s) in skin and liver after being exposed to 31.0 °C seawater (sub-lethal stress test) were measured as parameters of tolerance to high temperature stress. In the lethal stress test, the fish fed the diet with 1000 mg LF supplemented group showed significantly longer LT50 compared to that of 0 mg LF group, but other LF supplemented groups did not show any significant differences on the LT50 from 0 mg LF group. In the sub-lethal stress test, significantly higher level of HSP70s was measured in skin collected from the fish fed the diet with 1000 mg LF supplemented group. The fish fed 400 and 1000 mg LF supplemented diets showed significantly higher levels of liver HSP70s compared to that of 0 mg LF group. In conclusion, dietary LF supplementation enhances the tolerance to high temperature stress in Japanese flounder juveniles.