Feeding habits, monthly and ontogenetic diet shifts of hairtail, Trichiurus margarites (Pisces:Trichiuridae), in the Beibu Gulf of South China Sea

To advance the understanding of hairtail diet and its variations, an annual research was conducted. Stomachs of 666 hairtail, Trichiurus margarites Li 1992, sampled monthly from October 2008 to September 2009 in the Beibu Gulf of the South China Sea, showed Decapterus maruadsi to be the primary prey components of the diet. Small benthic fish, Bregmaceros rarisquamosus and B. nectabanus, and crustacean, Acetes chinensis, were also relatively essential, whereas the other 30 species were only present in comparatively lower percentages. The results revealed that the mean repletion index varied considerably by month, while trophic diversity appeared relative consistence. Mean repletion index increased in accordance with the hairtail gonad maturity stages. Nevertheless, the proportion of empty stomachs decreased with the stages. The 14 PL classes demonstrated significantly differences with respect to prey weight and numbers. The tendency of mean prey number and weight increased with the body size. Cluster analysis, based on IRI values for the above PL classes showed that the feeding habits of hairtail were relative heterogeneous among different sizes. In conclusion, the diet of T. margarites varied significantly by month and ontogenetic development. This information may later assist in the development and improvement of marine ecosystem modeling.