Feeding Habits Of Lake Anchovy (Coilia Ectenes) In Meiliang Bay, Taihu Lake: Stomach Content And Stable Isotope Analysis

Fish is one of the most important factors which affect lake ecosystem. The feeding of fish can help itself to maintain its own growth and development. At the same time, the feeding behavior of fish will affect the composition of the prey communities. Fish feeding habits study is essential for a rational utilization and management of fisheries resources, and it also can deepen our understanding of the structure changing of food web in lake ecosystem.In Meiliang Bay, Taihu Lake, the lake anchovy (Coilia ectenes) was collected monthly from fishermen in May, June, July, August and December,2009. Totally,106 individuals were collected (total length:114-282mm). Stomach content and stable isotope analysis were combined to study the food composition, feeding selectivity, feeding shifts and trophic position of lake anchovy. The results are as follow:The lake anchovy fed primarily on animal feeds, including copepods (Calanoid, Cyclopodia, Nauplius), cladocerans (Bosmina, Daphnia, Moina, Ceriodaphnia, Diaphanosoma), aquatic insects, small fish and shrimps.δ15N of lake anchovy were 4‰higher than zooplankton's and theirδ13C values were similar to that for zooplankton. This also suggests that the lake anchovy maybe feeds primarily on zooplankton.In terms of feeding selectivity, the lake anchovy preferred Calanoid and Daphnia, but avoided Cyclopodia, Nauplius, Bosmina, Moina and Ceriodaphnia.As the body length increased, we observed diet shifts of the lake anchovy. But these shifts were only existed in July and August. During this period, the large body size lake anchovy fed primarily on small fish while the small body size ones fed primarily on zooplankton. This was reflected by both stomach content and stable isotope analysis clearly.As the lake anchovy fed primarily on zooplankton and also fed on small fish sometimes, the tropic position of lake anchovy in the food web should be between secondary consumer and tertiary consumer. Using zooplankton as a baseline, we analyzed the tropic position of lake anchovy withδ15N. The result showed that the tropic position of lake anchovy was 3.2 which was accordance with the forward narrative. On the whole, the lake anchovy fed primarily on animal feeds and zooplankton was the most important food item. At the same time, we found that lake anchovy had strong positive selectivity to Daphnia and Calanoid. In recent years, lake anchovy became the absolute dominant fish in Taihu Lake; the production increased year by year and the body sizes of the individuals were getting smaller. All these made zooplankton under strong predation pressure. As a result, the controlling force of zooplankton on phytoplankton was weakened. This may be a factor which accelerates the development of eutrophication in Taihu Lake.