SEASONAL CHANGES OF FISH COMMUNITY COMPOSITION IN THE SUBTIDAL WATER IN THE MOUTH AREA OF YANGTZE ESTUARY

Based on the surveys of fishes in the subtidal water of the mouth area of Yangtze estuary between JuneNovember in 2006 and January-March in 2007,we analyzed the seasonal changes of fish community composition in this area.A total of 42 fish species belonging to 21 families were collected.The lengths of all fish species were almost lower than 20 cm,which meant the fish community composition mainly dominated by the young or small size fishes in the subtidal water areas.The guild of marine fishes(27species)has the largest number of species,followed by estuarine resident fishes(10species),while the other guilds of freshwater,anadromous and catadromous fishes had the lower number species.As for as the live layers of subtidal fishes,the most fish species was the demersal fishes(about 23species),followed by the surface or pelagic fishes(14species),lowest the lower level of fishes(only 5species).The dominant species contributing above 15% of the total fish abundance were spinyhead croaker Collichthys lucidus,estuarine tapertail anchovy Coilia ectenes,leading fish Harpodon nehereus in station S1,which was similar with station S2.It found that there was higher similar in fish community composition between station S1 and S2,so it suggested that no obvious difference existed in the subtidal fish community in the mouth area of Yangtze estuary.However,we also found that there were obviously seasonal changes in fish abundance and species between these two sampling stations.Using the methods of group average cluster analysis and nMDS ordination,the subtidal fish community was classified into groupⅠ(samples collected from winter to early spring)and groupⅡ(samples collected from summer to autumn).Through the SIMPER soft analysis on the fish community,we found the average similarity in groupⅠ was 63%and accumulative contribution of 5fish species was more than 90%,including Anguilla japonica,Collichthys lucidus,Coilia ectenes.In groupⅡ,the average similarity was 44.2%and accumulative contribution of 7fish species was more than 90%,such as Collichthys lucidus,Coilia ectenes,Harpodon nehereus,Trypauchen vagina,Odontamblyopus rubicundus,Stolephorus chinensis and Setipinna taty.Moreover,the average dissimilarity between the two groups reached73.03%and the accumulative contribution of 17 fish species was more than 90%,such as Japanese eel Anguilla japonica,spinyhead croaker Collichthys lucidus,spear tail goby Chaeturichthys stigmatias,estuarine tapertail anchovy Coilia ectenes,Joyner' s tonguesole Cynoglossus joyneri and leading fish Harpodon nehereus.