EFFECTS OF DAILY PHOTOPERIOD ON FEED CONSUMPTION, DIGESTIVE ENZYME ACTIVITIES AND BLOOD HORMONE OF TURBOT SCOPHTHALMUS MAXIMUS L. JUVENILES

This study was conducted to investigate the effects of 4 kinds 24L﹕0D (D1), 16L﹕8D (D2), 8L﹕16D (D3), 0L﹕24D (D4) of photoperiods on feed consumption, digestive enzyme activities and blood hormone of turbotScophthalmus maximus L. juveniles with initial body weight of (30.5±2.0) g in 20 hours (8:00am—4:00am). The results showed that the feed rate decreased with the shorten of illumination time, and feeding peak in D1 group appeared every 8h, meanwhile others appeared at 8:00am and 4:00pm. Activities of protease and amylase of former 3 groups were appeared spike at 12:00am and 8:00pm, and lipase was significantly higher than that of the D4 group. There were no difference of GH contents from 8:00am to 8:00pm among all groups, and D1 group at 4:00am was significantly higher than others, but D4 group was significantly lower than others from 0:00am to 4:00am. COR contents of D1, D2 and D3 groups were not significant difference in 8h after first feeding, and then increased firstly and decreased afterwards; D4 group reached the maximum level at 8:00pm. NE content of D1 and D2 groups were significantly higher than that of the others at 0:00am, meanwhile D4 group was significantly lower than others at 8:00pm. T3 content of D2 group was significantly higher than that of the other groups at 8:00am and 12:00am; D4 group was lower at 8:00pm, and higher at 0:00am than others; D2 and D3 group were lower than those of D1 and D4 group at 4:00am; The highest values of T3 of all groups were appeared at 8:00pm. These results demonstrated that feed intake, digestive enzyme activities and serum hormone contents of turbot juvenile were affected by photoperiod under current experimental conditions. 8—16 lighting period and feed twice daily would be recommended for turbot culture under this intensity of illumination.