Diet composition and feeding habits variation with body length of Chelidonichthys spinosus in central and northern East China Sea

Abstract

Chelidonichthys spinosus is an important benthic fish species which distributes from the Bohai Sea to the South China Sea.From May 2008 to February 2009,total of 382 C.spinosus samples with body length of 39-427 mm were collected from Zhoushan fishing ground,Zhouwai fishing ground,Jiangwai fishing ground and Yushan fishing ground,all of which are located in central and northern East China Sea.Based on stomach contents analysis,diet composition and ontogenetic variation in feeding of C.spinosus in central and northern East China Sea were investigated by applying cluster analysis,one-way ANOVA and chi-squared test.More than 93 species of prey were ingested by C.spinosus.Natantia,Euphausiacea and Pisces were the most important prey groups,accounting for 92.19%,30.08% and 21.49% of the occurrence frequency;20.37%,4.55% and 62.56% with the number percentage,51.01%,35.13% and 2.08% with the weight percentage and 563.09,170.59 and 1 308.55 with the index of relative importance(IRI) of the total food,respectively.At species level,the dominant preys were Euphausia pacifica,Parapenaeopsis tenella,Crangon affinis and Chaeturichths hexanema.E.pacifica showed the most occurrence frequency,accounting for 20.31%;E.pacifica was the largest in number,accounting for 62.34%;P.tenella had the highest weight percentage,accounting for 13.60%.The highest percentage of IRI of total food was presented in E.pacifica(1 308.17),followed by P.tenella(IRI=141.53),C.affinis(IRI=124.17) and C.hex-anema(IRI=29.11).The feeding intensity,as indicated by percentage of empty stomachs(PES) and mean stomach fullness index(MSFI),varied significantly among different size classes,while the diet composition of major prey groups also varied significantly.The weight of prey fish increased significantly with fish size increasing.For fish shorter than 200 mm,the dietary breadth positively correlated with body length,while for fish longer than 200 mm,it showed negatively correlation with body length.However,mean weight of each prey increased with fish size increasing.This phenomenon is consistent with the "optimum foraging theory".Cluster analysis revealed two major groups of body length in 39-427mm range: one group consisted of specimens shorter than 100 mm,the other group longer than 100 mm.Furthermore,the groups whose body length was more than 100 mm also clusted into two major groups: one of which was less than 200 mm in body length,and the other was more than 200 mm.As far as the species level was concerned,C.spinosus with body length less than 100 mm mainly take Iiella pelagicus and Leptochela gracilis for food,the other longer than 100 mm mainly take E.pacifica,P.tenella,C.affinis,C.hexanema and Oratosquilla oratoria for food.The proportion of fish in the diet composition signifi-cantly increased with body length increasing.It can be concluded that the feeding habits variation of C.affinis is closely related with its body length.