Abstract:In order to understand the species composition and abundance distribution pattern of fish eggs and larvae in the East China Sea ecosystem and their relationship with physical environmental factors,based on the data of five ichthyoplankton and physical environment surveys in the East China Sea in different seasons during November 2006 to June 2008,the seasonal and inter-annual variation of species composition and abundance distribution pattern of fish eggs and larvae,and the seasonal and inter-annual variabilities in physical environment of spawning grounds and their impacts on the distribution pattern of the spawning grounds,species composition and abundance distribution patterns of fish eggs and larvae have been discussed.The result showed that a total of 74 813 fish eggs and 16 826 fish larvae belonging to 135 taxa were collected,of which,109 taxa have been correctly identified to species level,which belong to 99 genera,67 families and 15 orders;while 17 taxa can only be identified to genus level,6 taxa only identified to family level and 3 taxa identified to order level.There was a tendency toward increased species number and amount of fish eggs and larvae from autumn,winter to spring during 2006 to 2007;whereas,the species number and amount of fish eggs and larvae for samples collected in spring 2008 were significantly lower compared to those collected in spring 2007.Though the species number of fish eggs and larvae for samples collected in spring 2008 were almost the same as in early summer 2008,the amount of fish eggs were significantly larger in early summer compared to spring,on the contrary,the amount of fish larvae in early summer were almost the same as in spring 2008.Species composition of the forty-two dominant species,important species and main species are the major components of fish eggs and larvae distributed in the East China Sea currently.Studies of the physical environment in the East China Sea showed that changes in patterns of sea surface temperature and salinity were markedly different among seasons.In the research domain,the order in which the sea surface thermal front intensity varied with seasons from the strongest to the weakest was autumn-winter,spring and early summer;the distance from the frontal areas to the coastal also varied with seasons from the nearest to the farthest was autumn,winter,spring and early summer,meanwhile the frontal areas run southward in winter and run northward in summer.The sea surface saline front mostly lies close to the shore and usually runs parallel to the shoreline.The surface saline front intensity varied with seasons,most visible in winter,whereas some wane in early summer before regaining strength in autumn.The autumn-winter water temperatures in deep shelf sea areas were higher than coastal waters,and then the spawning stock moved to offshore deep-warm waters and spawned there.The water temperature in coastal waters remarkably increased in spring and the highest value was recorded in the early summer.Then the spawning stock exhibited some form of an inshore spawning migration,and the spawning ground expanded from deep shelf sea areas to coastal waters and formed inshore spawning centers.The abundance distribution patterns of the fish eggs and larvae were closely related to the surface thermal and saline fronts,also species-specific temperature-salinity tolerance.In general,fish eggs and larvae were distributed according to the spreading of the warmer surface waters and gathered at the warm side of the thermal front,with species-specific optimal temperature-salinity.Ocean environmental conditions such as temperature and salinity,and the reproductive biology of each species were the main causes of variation in species composition and distribution patterns of fish eggs and larvae among different surveys.Optimal temperature-salinity range,convergence and entrainment in the frontal area and the biological characters of the species all play the importand role in the formation of high density areas of fish eggs and larvae.