The Coilia mystus, estuary migratory and subject to the Family Engraulidae, mainly distributed along the coastal waters, especially in bay and estuary, is a very important small economic fish. One of the main spawning grounds is located from Yangtze River to Hangzhou bay. Stow net with double stake can be used to harvest it in fishing season. Early research about feeding habits of C. mystus, studies on the food of C. mystus (L.), showed that C. mystus mainly feed on Crustacean, of which Copepods first place, Mysids and Decapoda second. Besides, some references about biological characteristics of C. mystus were referred to feeding habits. However, there have been little exclusive studies on its feeding habits, besides the quantitative analysis studies on C. mystus.
In order to investigate the diet of C. mystus, 1355 specimens were collected from the Yangtze River estuary and Hangzhou bay from June to August, 2009. The stomach contents of the specimens were classified as soon as possible after the collection. Multivariate statistical techniques were used to analyze data on stomach contents and zooplankton composition in the sampling waters. In this paper, index of relative importance (IRI) and percentage index of relative importance (%IRI) were used to depict food species or food groups. Dominance and percentage average abundance were used to determine the dominant species and major groups. Similarity index were performed to analyze their food list from the stomach contents and the zooplankton composition list from the sampling waters, which were collected from the same locations during the fish specimens collection. When the major zooplankton species were concerned, the index of relative importance of Acanthomysis longirostris, a brackish estuarine species, is 703.25, which accounted for 39.65% of total IRI of dominant species, much higher than the other species, even the copepod; therefore, it was the most important species in the food list of C. mystus. The other major species in the stomach contents were Schmackeria poplesia, Labidocera euchaeta and Tortanus vermiculus, with the IRI of 261.04, 107.53 and 27.27, respectively. Therefore, the four above mentioned species were the dominant diet of the C. mystus, which accounted to 61.96% of total IRI. The similarity value of the stomach contents and the sampling zooplankton was 0.363-0.365, while the similarity value of copepod between the food diet and the sampling zooplankton was 0.521-0.575. Based on above facts, we speculate that C. mystus filters the smaller copepods as food with less selectivity; however, to the larger Mysidacea species, it prefers to pursue them in a much selective way.