盐度胁迫和昼夜变化对鲻鱼幼鱼消化酶活力的影响

研究了S0（盐度为0）、S10、S20、S33（对照）和S40 5个盐度梯度14 d内盐度胁迫及其昼夜变化对鲻鱼（Mugil cephalus）幼鱼蛋白酶和淀粉酶比活力的影响。结果显示：1）盐度胁迫对鲻鱼幼鱼的消化酶活力有显著影响（P0.05）。不同盐度的蛋白酶和淀粉酶活力的变化规律都是在第0天~第7天升高，第7天~第14天降低，最终时（第14天）S0~S33蛋白酶活力呈上升趋势，S33~S40下降；S0~S20淀粉酶活力差异不显著（P0.05），S20~S33呈上升，S33~S40下降，且差异显著（P0.05）；2）对鲻鱼幼鱼消化酶活性昼夜变化的测定表明，蛋白酶和淀粉酶活性的最高值分别在12:00和15:00，最低值均出现在6:00。因此，夜间设置定时投喂，可促进鱼类快速健康生长。

Effects of salinity stress and diurnal variation on digestive enzyme activity of juvenile grey mullet Mugil cephalus

We studied the effects of salinity stress and diurnal variation on the protease and amylase activity of juvenile grey mullet (Mugil cephalus). Five different salinities were set: S0 (salinity is 0), S10, S20, S33 (control) and S40, respectively. The results indicate: 1) salinity stress has significant effects on activity of digestive enzymes (P0.05). Activity of protease and amylase increased within 0~7 d, then decreased within 7~14 d. At the last day (14th day), protease activity of S0~S33 increased while that of S33~S40 decreased. The difference of amylase activity of S0~S20 is insignificant (P0.05), andamylase activityof S20~S33 increased while that of S33~S40 decreased significantly (P0.05); 2) The diurnal variation in activity of digestive enzyme of M.cephalus reveals that the protease and amylase activity reached the maximum at 12:00 and 15:00, respectively, while bottomed at 6:00. Thus, feeding periodically at night can help the fish grow fast and healthily.