To ascertain the early food resource use of the endangered sleeper, Eleotris oxycephala , the food habits of juveniles were studied in a major stream (which received treated sewage discharge and had a low level of vegetation cover) and a tributary (which received little artificial inflow and had extensive vegetation cover) in the Sagami River system, eastern Japan in November 2015 (winter), May 2016 (spring), and August/September 2016 (summer). The stomach content compositions of 174 individuals and the stable isotope ratios of 30 individuals and their prey animals were investigated along with the species composition of prey animals in the environment. Various aquatic animals, including fish eggs, mollusks, crabs, palaemonid shrimps, atyid shrimps, isopods (asellids), chironomid larvae, and dragonfly larvae, were present in juvenile E. oxycephala stomach contents. In the tributary, they mainly preyed on atyid shrimps, which were abundant in the environment, with lower feeding intensity during winter season. In the major stream, throughout the year (including winter), they fed mainly on chironomid larvae, which were smaller and slower than atyid shrimps, and so easily caught, even by small recently recruited juveniles. There were abundant chironomid larvae in the major stream environment, where the water temperature seemed warmer and more eutrophic than in the tributary because of the treated sewage discharge, particularly in winter. These results indicated that feeding intensity differed between sites, particularly in winter, and this difference might be associated with differences in prey availability (i.e., chironomid larvae) or warm-water conditions. Moreover, juveniles could shift their use of food resources, in response to differences in prey availability. Thus, to conserve E. oxycephala in terms of early food resource use, it is necessary to conserve various aquatic prey animals such as atyid shrimps and chironomid larvae and their habitats.

中文翻译：

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日本相模河水系濒临灭绝的沉睡动物 Eleotris oxycephala 幼鱼的食物资源利用

为了确定濒临灭绝的卧蚕的早期食物资源利用，研究了一条主要河流（接受处理过的污水排放，植被覆盖水平低）和一条支流（几乎没有人工流入）的幼鱼的饮食习惯。 2015 年 11 月（冬季）、2016 年 5 月（春季）和 2016 年 8 月 / 9 月（夏季）在日本东部的相模川系统中具有广泛的植被覆盖。研究了174只个体的胃内容物组成和30只个体及其猎物的稳定同位素比值，以及环境中猎物的物种组成。幼鱼中存在各种水生动物，包括鱼卵、软体动物、螃蟹、古对虾、atyid 虾、等足类（asellids）、摇蚊幼虫和蜻蜓幼虫。oxycephala 胃内容物。在支流中，它们主要捕食环境中丰富的虾类，冬季摄食强度较低。在干流中，全年（包括冬季），它们主要以摇蚊幼虫为食，这些幼虫比阿特伊德虾更小、速度更慢，因此很容易被捕获，即使是最近招募的小型幼虾。干流环境中有大量摇蚊幼虫，尤其是在冬季，由于处理后的污水排放，干流环境中的水温似乎比支流中更暖和更富营养化。这些结果表明不同地点的摄食强度不同，特别是在冬季，这种差异可能与猎物可用性（即摇蚊幼虫）或温水条件的差异有关。而且，少年可以改变他们对食物资源的使用，以应对猎物供应的差异。因此，从早期食物资源利用的角度保护E. oxycephala，有必要保护各种水生猎物，如atyid 虾和摇蚊幼虫及其栖息地。