饥饿胁迫条件下黑(鱼免)(Miichthys miiuy)仔鱼的生长与存活过程研究

EFFECTS OF DELAYED FIRST FEEDING ON GROWTH,SURVIVAL AND BIOCHEMICAL COMPOSITION OF CROAKER MIICHTHYS MIIUY LARVAE

采用实验生态学方法研究了延迟投饵对黑(鱼免)仔鱼摄食、存活生长及体成分组成的影响。结果表明,在24℃,仔鱼在3日龄时开口摄食,4日龄时卵黄囊吸收完毕,6日龄仔鱼如不能建立外源性营养即进入饥饿死亡不可逆点(PNR),而延迟投饵3天(6日龄)以上的仔鱼在8日龄前全部死亡。正常投喂仔鱼(16%)和延迟投饵1天仔鱼(15%)的存活率明显高于延迟2天投饵仔鱼(9%)。它们的高死亡(日死亡率为5%—6.5%)集中发生在3—8日龄期间,但低于3—7日龄内延迟投饵3天和完全饥饿仔鱼(日死亡率为18.5%)。在7日龄时,正常投喂仔鱼(9.9%)的特殊生长率(SGR)明显高于延迟投饵仔鱼(4.6%—8.4%)。在36日龄时,正常投喂仔鱼与延迟投饵1天仔鱼之间的生长差异消失,与延迟投饵2天的仔鱼之间的生长差异显著。延迟投饵引起开口摄食阶段仔鱼体内脂肪和蛋白质含量明显减少,但延迟投饵1—2天的存活仔鱼在后期发育过程中可以达到正常投饵仔鱼的营养水平。因此,不论在养殖条件下还是在自然水域,黑(鱼免)仔鱼必须在开口后2天之内建立起主动摄食能力才可能保证其仔鱼的正常发育、生长和存活。

Effects of the timing of first feeding （3, 4, 5, 6 dah and no fed） on the feeding growth, survival and biochemical composition of croaker Miichthys miiuy larvae were investigated at 24℃ under laboratory conditions. The larvae started to open mouth and started feeding on 3 days after hatching （dah）. Yolk absorption was completed on 4 dab and the larvae reached PNR or irreversible starvation age on 6 dah （2d after yolk exhaustion）. Larvae first fed on 3 and 4 dah （15%-16%） survived apparently better than those fed on 5 dab （9%） at the end of the experiment （36dah）. High larval mortality occurred from first feeding time to 7 dah in all treatments, accounting for 40% （first fed prior to 5 dah larvae） to 90% （first fed on 6 dah and no fed larvae） of the total mortality throughout the experiment. No larvae first fed after 5 dah could survive to 8dah. Larvae first fed on 3 and 4 dah had apparently better growth performance （SGR = 5%） than those first fed on 5 dah （4%）. Similarly, the individual size variation （CV of the final Lt） of the larvae decreased from 13-15 in the former two groups to 11 in the latter ones. However, neither larval survival nor growth showed noticeable differences between the 3 and 4 dah feeding groups. On 36dab, the percentages of either crude protein or lipid of the larvae body had no significant difference among the 3, 4, and 5 dah feeding groups. These results indicate that delayed first feeding up to ld after yolk absorption could lead to adverse survival and growth of croaker larvae but showed negligible influences on the nutritional status of the survivors. To avoid potential starvation mortality for better growth, feeding the larvae should be started within ld after yolk absorption at 24℃.