Diet And Trophic Level Of Crimson Seabream, Paragyrops Edita Tanaka, In The Beibu Gulf Of South China Sea

Crimson seabream, Paragyrops edita Tanaka, is one of the crucial coastal demersal predators in the Beibu Gulf, South China Sea. The search of the food composition, variation of feeding intensity and trophic level of crimson seabream, Paragyrops edita Tanaka, show the relative position that crimson seabream, Paragyrops edita Tanaka locate in the food chain, variation of trophic level, the variation of the abundance ratio of the food organism in the marine inverinment and the variation of the community structure of the fishes. Supply the theory evindence for the reaserch of the energy fluxion and the rule of the substance transformation of the marine ecosystem in Beibu gulf.To explore the Diet and trophic level, we sample the samplemans from the trawl fishing in Bubei gulf, South China Sea. A total of 909 individuals of P. edita, ranging from 37 to 261mm in standard length and 1.7g to 701.1g fresh in body weight, were collected from monthly sampling of bottom trawl fisheries in Guangxi Zhuang Autonomous Region during August 2008 and Sept 2009(except Jun and Jul 2009, fishing is banned). And a total of178 individuals of P. edita of Moth of Beibu Gulf, South China Sea, ranging from 90 to 217mm in standard length and 31.6 to 423.1g fresh body weight, were collected from sampling of bottom trawl fisheries in Provinces of Hainan Dec 2008, Mar 2009 and Aug 2009. The results are as followings:1 According to the analysis of stomach content, P. edita of Beibu Gulf mainly feeds fish (Bregmaceros macclellandii, Stolephorus commersonii) followed by echinoderms, crustaceans ( Penaeus, Brachyura, Acetes japonicus Kishhinouye, Euphausiacea, Mysidacea, Lucifer, Amphipoda, Rotifera, Cladocera, Copeppoda), Mollusca(Bivalvia, Gastropods, Cephalopoda), polychaetes, Sagitta nagae, protozo, etc. Twenty-three prey items have been identified to the species level.2 The dietary composition of P. edita from Beibu Gulf varied with the increase of body size. With the size increaseing, the swimming animal replaces the zooplankton which is easy to be digested, the huge prey replace the small one, the high trophic prey replace the low trophic prey. Cluster analysis revealed that clear feeding shifts occurred at the body size of 60mm, which indicated that diet spectra gradually changed from the zooplankton-dominated (Cladocera, Copeppoda) at 30-60mm body size to nekton-based (Bregmaceros macclellandii, Stolephorus commersonii) and some other large crustacean(Penaeus, Brachyura)at greater-than 60mm body size. The proportion of empty stomachs(Χ~2=67.82 p<0.05) is varied with the increase of body size; the IFI(Χ~2=96.13, p<0.05)is varied with the increase of body size , IFI increase gradually with the body size increasing, the big fishes'IFI is higher than small fish. The index of Shannon-Wiener H'(Χ~2=7.09, p>0.05)is not varied with the body size change; the evenness J(Χ~2=3.4, p>0.05)'is not varied with the body size change too.3 The dietary composition of P. edita from Beibu Gulf does not possess seasonal change (Χ~2=2.32,p>0.05), all feed the fish as the dominating food; the proportion of empty stomachs(Χ~2=12.19, p<0.05)possesses the seasonal change; the IFI(Χ~2=7.55, p>0.05)does not possess the seasonal change too.4 The dietary composition of P. edita from Beibu Gulf is not visibly varied with the develop of gonad (Χ~2=7.37,p>0.05), all feed the fish as the dominating food; The proportion of empty stomachs(Χ~2=2.27, p>0.05)is not visible varied with the develop of gonad; the IFI(Χ~2=30.04, p<0.05)is visible varied with the develop of gonad.5 The dietary composition of female P. edita in Beibu Gulf and male P. edita are not visible different(Χ~2=7.37,p>0.05), all feed the fish as the dominating food. The proportion of empty stomachs and the IFI in male P. edita's is higher than those of in female P. edita.6 The dietary composition of P. edita mainly feeds Penaeus and fish in the Mouth of Beibu Gulf. The amount of the category of the Mouth of Beibu Gulf P. edita is visible less than the amount of the category of P. edit in Beibu Gulf female a. There is visible different between the dietary composition of P. edita in the Mouth of Beibu Gulf and P. edita in the Beibu Gulf (Χ~2=8.91,p<0.05).