Feeding Rates Affect Expression of Heat-Shock Protein 70 in Green Sturgeon Fry

Two growth trials were conducted to determine the effect of feeding rate on the responses of a heat-shock protein (hsp70) in the fry of Green Sturgeon Acipenser medirostris. Four tanks were randomly assigned to each feeding treatment: 2.5, 5.0, 7.5, 10.0, 12.5 and 15.0% of body weight/d in trial I and 2.0, 3.0, 4.0, 5.0, 6.0 and 7.0% of body weight/d for trial II. The fry were raised indoor at 18 degrees C and fed a commercial salmonid soft-moist diet. Densities were 50 fry/tank in trial I fed for 49 d posthatch (dph) and 30 fry/tank in trial II fed for 70 dph. At the end of 1 week of feeding, five fish from each tank were subjected to heat shock by increasing the water temperature from 18 degrees C to 28 degrees C at a rate of 4 degrees C/h and then holding at 28 degrees C thereafter for 4 h before tissue samples were collected. Heat shock induced significant changes in the levels of hsp70 in the liver and white muscle of fish in all feeding treatments. However, feeding rate treatments had no significant effect on the basal and heat-shocked levels of hsp70 in the liver of these fish. The lowest feeding rate significantly depressed the induced level of hsp70 in the muscle of Green Sturgeon. A feeding rate of 10.0% of body weight/d is suggested for Green Sturgeon at 49 dph and 6.0% at 70 dph, based on their maximum responses of hsp70 in white muscle tissue. This study indicates that the response of hsp70 in the liver and muscle of Green Sturgeon is sensitive to heat-shock stress. The effect of different feeding rates on the response of hsp70 is also tissue-dependent. This variation should be considered when hsp70 is used as a biomarker to evaluate heat-shock response.