Abstract: The present study explored the feeding ecology of the larvae and juveniles of Japanese Spanish mackerel (Scomberomorus niphonius) collected from Xiangshan Bay between April 3th and June 10th in 2015. In order to obtain sufficient quantity of individuals in different development stages, larvae and juveniles were sampled weekly by frame net (1 m×2 m, 1.0 mm mesh size). A total of 1108 individuals were collected across the study, having body length of 4.0-41.1 mm; 587 intact specimens among them were used to investigate the feeding ecology of the larvae and juveniles by gut content analysis. A total of 11 prey species were found in guts, and fish larvae were the dominant preys (98.6%), which mainly consisted of Konosirus punctatus, Gobiidae and Chelon haematocheilus. Except yolksac larvae, the feeding incidences were 62.0%, 81.3%, 80.0%, and 86.8% in pre-flexion, flexion, postflexion larval and juveniles, respectively. The gapesize of larvae and juveniles significantly correlated with its body length, and the rate of the gapesize relative to body length ranged from 16.4% to 25.1%. The mean size of the prey increased accordingly as the predator S. niphonius grew, which also showed significant correlation with body length and gapesize. The average length for prey ranged from 2.6 mm in yolksac larval to 11.2 mm in juveniles. There were three peaks for the density of dominant prey items in Xiangshan Bay, and S. niphonius mainly appeared in the second peak of prey abundance during the study period. The variation of S. niphonius was synchronized with that of prey item density.

Key words: seasonal variation, Yangtze River Estuary., invertebrate, environmental factor, assemblage structure