Engraulis japonicus, an important fishery resource, is a key species in ecosystem trophodynamics studies. In this study, we examined stomach content of E. japonicusby stable isotope analyses, with samples collected from the East China Sea in 2008-2009 and 2020. The aim of this study was to demonstrate their diet composition, diel and ontogenetic changes in feeding habits and trophic level. Results of the stomach content analysis showed that E. japonicus mainly fed on planktonic crustaceans and small fish. The main prey species were Euphausia pacifica [index of relative importance (IRI)=87.6%; frequency(F)=57.6%], Paracalanus parvus (IRI=3.2%, F=15.3%), and Themisto gracilipes (IRI=2.1%, F=13.1%). Results of the stable isotope analysis showed that Copepoda were the main food source of E. japonicus, followed by Euphausiacea, and the contribution rate of Amphipoda was the least, which was less than 1%. There was significant diel change in diet composition. Feeding intensity was higher in the daytime than at night, with the highest in the dusk and the lowest at midnight. Ontogenetic change in feeding habit occurred when fork length reached 90 mm, over which the fish fed both zooplankton and small fishes. The δ13C of E. japonicus was between -21.66‰ and -18.14‰, with an average of (-19.92±0.86)‰. The δ15N of E. japonicus ranged from 4.07‰ to 10.78‰, with an average of (8.14±2.48)‰. Both δ13C and δ15N values were positively correlated with fork length. Trophic level of the fish was 3.4 with stomach content analysis and 2.7 with stable isotope analysis. The results would provide important reference for understanding nutritional status of pelagic small fish, and offer some basic data to establish ecopath model.
鳀是重要的渔业资源捕捞对象,同时也是生态系统营养动力学研究的关键种。基于2020年和2008—2009年东海区采集的鳀样品,结合胃含物分析和肌肉碳、氮稳定同位素技术,分析了鳀的食物组成、食性昼夜差异、不同发育阶段的食性转变及其营养级,研究鳀的摄食生态。胃含物分析显示,鳀主要摄食浮游甲壳类和小型鱼类,优势饵料依次为太平洋磷虾[相对重要指数百分比(IRI)=87.6%,出现频率(F)=57.6%]、小拟哲水蚤(IRI=3.2%,F=15.3%)和细足法虫戎(IRI=2.1%,F=13.1%);同位素分析显示,桡足类是鳀的主要食物来源,其次是磷虾类,端足类的食源贡献率最小,不足1%。鳀食物组成昼夜差异明显,摄食强度白天比晚上高,下午最高,午夜最低;叉长90 mm是鳀食性转变的拐点,小于90 mm的鳀主要摄食浮游动物,大于90 mm的鳀主要摄食浮游动物,兼食小型鱼类。鳀的δ13C值范围为-21.66‰～-18.14‰,平均值为(-19.92±0.86)‰;δ15N值范围为4.07‰～10.78‰,平均值为(8.14±2.48)‰;鳀的δ13C和δ15N比值与叉长呈极显著正相关。基于胃含物分析的鳀营养级为3.4,基于δ15N稳定同位素的鳀营养级为2.7。本研究可为中上层小型鱼类在生态系统中的营养地位提供参考依据,为构建食物网营养通道提供基础资料。.
Keywords: