Biodiversity Of Icefishes And Feeding Traits Of Neosalanx Taihuensis In Lake Liangzi

We have conducted a dynamic investigation among 11 sampling sites in Lake Liangzi in the period of August,2006 to March,2008.Our purpose is to find out the diversity status,temporal variations of icefsih assemblage and their food organisms.Totally two genera,three species of icefishes were identified.They are Neosalanx oligodontis,Neosalanx taihuensis and Hemisalanx brachyrostralis.The two Neosalanxs showed the same habitat usage(p＜0.05) with a higher occupation rate than the other species.N.oligodontis was the most dominant one(P_i = 0.69) in this lake area,N.taihuensis ran secondly(P_i = 0.28) and H.brachyrostralis showed the lowest density(P_i = 0.03).In general,individual density in the eastern lake area(90%) was higher than that in the western lake area(10%).Pelagic algae are an important indicator for environmental changes and are essential to filtering fishes as food resource.In our sampling period,Crustacean zooplanktons were sampled and checked.Totally 22 crustacean species,which were composed of 16 Cladoceta species and six Copepoda species,were identified. These species belong to nine families and 18 genera,nine of which were recorded for the first time in this lake area.Analysis of the species dominance index(Y),Shannon-Wiener diversity index(H),number of species(S), species richness index(D) and individual density(ind./L) revealed significant seasonal variation of the crustacean diversity.Daphnia hyaline(Y = 0.80±0.01),Daphnia cristata(Y = 0.50±0.03) and Bosmina longirostris(Y=0.58±0.04) were the dominant Cladoceta species in spring,summer and autumn-winter respectively.Neodiaptomus yangtsekiangensis(Y=0.41±0.01),Cyclops vicinus(Y = 0.46) to Neutrodiaptomus incongruens(Y=0.65±0.18) were the dominant Copepod species in summer,autumn and winter-spring respectively.Population density of Crustacean declined gradually from 292(±85,S.D.) to 169 (±104),140(±53) and 120(±0) through spring to winter.Similarly,species diversity remained low in winter and spring(S≤12,D=0.77 and 0.71,H=1.79 and 1.45,respectively),but increased in summer and autumn(S≥17,D = 0.98 and 0.88,H = 1.78 and 1.83, respectively).Further analysis indicated that species composition and diversity indexes of Crustacean community were relatively stable between 2006 and 2007 summers(August),as well as between 2007 and 2008 springs(March).Our results indicated that Lake Liangzi was in good condition for Crustacean species.Intestinal food analysis indicated that Copepods and Cladoceta species were the main food components for N.taihuensis.And the former showed much higher priority in icefish food selecting.