| Fish feeding habit analysis is fundamental for studying the structure and function of marine ecosystem, which provides an elemental assement for conducting fishery management. In this study, diet composition and feeding preference, changes of diet composition in different development stages, relationship between gut content and in situ species composition, food competition among different fish species and their trophic level were analyzed based on samples collected from Beibu Gulf in July2012. Moreover, annual trophic level variation was also discussed. The main results were as follows:1Stomach contents of309individuals from9fish species showed that there were13food groups in Decapterus maruadsi,4in Trachurus japonicus and Pennchic argentata,7in Acropoma japonicum and Upeneus japonicus,14in Polydactylus sextarius,2in Evynnis cardinalis,8in Psenopsis anomala, only1in Saurida tumbil, respectively. There were4feeding types of these9species, namely planktivorous fish, including Decapterus maruadsi, Trachurus japonicus, Acropoma japonicum and Polydactylus sextarius; benthic-feeding fish, including Evynnis cardinalis, Psenopsis anomala and Upeneus japonicus; piscivorous fish, only Saurida tumbil; omnivorous fish, only Pennchic argentata.2Changes of diet composition with individuals of different body length showed that amount of Copepoda and Macrura increased in Decapterus maruadsi with body length increasing; Acropoma japonicum with body length over70mm preferred larger prey, even cannibalism occurred in one individual whose body length arrived80mm; quantity of Copepoda and Macrura decreased in Polydactylus sextarius with body length increasing, showing insignificant preference of larger prey. The other6species didn’t show obvious prey preference.3Analyses of fish maturity stage determined by visual examination showed that all specimens varied from stage I to V, mostly in stage I and II, while Trachurus japonicus and Evynnis cardinalis only in stage I. The only one stage Ⅱ specimen of Decapterus maruadsi had empty stomach. Saurida tumbil feed on only fishes in all development stages. The other5species showed higher food diversity before maturation than those during or after maturation.4Fish stomach contents were significantly related to environmental species composition. Higher in situ species diversity always resulted in more food species in stomach; quantity of prey in stomach was affected by in situ prey abundance. Decapterus maruadsi, Trachurus japonicus, Acropoma japonicum and Polydactylus sextarius had strong preference in selective predation of Copepoda, while Evynnis cardinalis, Psenopsis anomala, Upeneus japonicus, Pennchic argentata and Saurida tumbil didn’t show preference of Copepoda.5Diet overlap analyses showed that diet overlap index (E) of Decapterus maruadsi, Trachurus japonicus, Polydactylus sextarius, Evynnis cardinalis, Psenopsis anomala and Pennchic argentata was relatively high because of the common preference of Marcrura; high overlap index of Upeneus japonicus and Pennchic argentata was caused by the common preference of Trachypenaeus curvirostris.6The trophic level determination by stomach analysis method showed that the trophic level of planktivorous fish (Decapterus maruadsi, Trachurus japonicus, Acropoma japonicum and Polydactylus sextarius) was3.4～3.7; benthic-feeding fish (Evynnis cardinalis, Psenopsis anomala and Upeneus japonicus) was3.7～3.8; piscivorous fish (Saurida tumbil) was4.0～4.5; omnivorous fish (Pennchic argentata) was3.8, respectively. Stable isotope analysis revealed similar result to stomach analysis.7Trophic level of Decapterus maruadsi and Trachurus japonicus were relatively constant, while Evynnis cardinalis, Psenopsis anomala and Upeneus japonicus increased by0.3-0.4, and Saurida tumbil decreased by0.3～0.8compared to the results from a decade ago. |
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