黄海中部小黄鱼摄食习性的体长变化与昼夜变化

Ontogenetic and diel variation in feeding habits of small yellow croaker Pseudosciaena polyactis Bleeker in the central part of Yellow Sea

根据2001年3月至2002年1月在黄海中部海域进行的4个季节的定点底拖网调查,应用聚类分析、单因素方差分析和列联表检验等方法,对小黄鱼(PseudosciaenapolyactisBleeker)摄食的体长和昼夜变化进行研究。结果表明:摄食强度没有明显的体长变化,而食物组成却有明显的体长变化。随着体长的增大,鱼类和虾类的比例有所增加,而磷虾类、桡足类和端足类的比例则减少。饵料生境宽度在体长大于109mm后有明显的增加。经检验,小黄鱼平均每个胃中含有的饵料个数显著减少而饵料重量则增加,这符合"最佳摄食理论"。聚类分析的结果表明,小黄鱼在体长达到109mm时,出现了明显的食物转换现象。小黄鱼的摄食强度在各个季节都有明显的昼夜变化,午夜24:00和早晨08:00是2个摄食高峰期。

A total of 1 688 specimens of small yellow croaker, Pseudosciaena polyactis Bleeker, at standard length (SL) of 80-178 mm, were sampled from seasonal bottom trawl surveys by the R/V ‘Bei Dou’ in the central part of Yellow Sea from March 2001 to January 2002. The ontogenetic and diel variation in the feeding ecology of small yellow croaker in the central part of Yellow Sea were examined by applying the cluster analysis, one-way ANOVA and a chi-squared test. The results show that the feeding intensity, as indicated by the percentage of empty stomachs (PES) and mean stomach fullness index (MSFI), do not vary significantly among different classes of sizes. But the diet composition varied with fish size. The frequency of fish and decapods increased significantly with increasing fish size, whereas the frequency of euphausiids, copepods and amphipods decreased. The dietary breadth increased significantly for fish longer than 109 mm SL. The mean number of prey per fish decreased significantly with the increase of fish size, while the mean weight of prey items per fish increased. This event is consistent with the “optimum foraging theory”. Cluster analysis revealed that there was an abrupt change in diet composition in the fish at about 109 mm SL. At species level, Euphausia pacifica, Calanus sinicus and Themisto gracilipes dominated the diet of fish smaller than 109 mm SL, whereas Thryssa kammalensis, Leptochela gracilis and Crangon affinis were the dominant prey for fish greater than 109 mm SL. The feeding intensity showed significantly diel variation during each season. The MSFI showed two main peaks at 0800 a.m. and 2400 p.m. in each season. The minimum value of MSFI in spring and summer occurred at 1200 a.m., and in autumn and winter at 1600 p.m. The PES at different time in each season was also different. The distribution of the PES showed an opposite tendency to the MSFI.