Study On The Morphological Identification Of The Commercial Fish Larvae And Juveniles In The Yangtze River Estuary

The Yangtze River Estuary is the largest estuary in China and has good hydrologic and physical conditions.The Yangtze River Estuary has a high primary productivity,which provides a powerful survival condition for marine fishes and other marine organisms.In recent years,human activities have caused some damage to the estuarine environment and affected the fish resources in the Yangtze River Estuary.The number of larvae directly affect the supply of fish.Therefore,the research on the species distribution and quantity of larvae and juveniles is one of the essential tasks in the sustainable utilization of fishery resources.The study of fish larvae and juveniles in the Yangtze River Estuary mainly concentrated on the species composition,community structure and abundance of the larvae and juveniles of the Yangtze Estuary and neighboring area.There is a lack of systematic arrangement for morphological characteries of fish larvae and juveniles in the Yangtze River Estuary.In this study,from March 2004 to March 2005,June 2006 to June 2007,August 2009 to August 2010,fish larvae and juveniles were collected by seine net(1m×4m,1mm mesh-aperture)in the surf zone of the Yangtze River Estuary,and from March 2014 to February 2016,fish larvae and juveniles were collected by larvae net(1.3m diameter,1mm mesh-aperture)in the southern branch of the Yangtze River Estuary.The morphology characteristics of commercial fish larvae and juveniles for identification were studied.From March 2004 to October 2010,a total of 67002 larval fishes of 108 species from 32 families were collected by seine net in the surf zone of the Yangtze River Estuary.Coilia nasus is most abundant species,followed by Pseudolaubuca sinensis,Acentrogobius pflaumi,Hemiculters,Tridentiger trigonocephalus.From March 2014 to February 2016,a total of 127653 larval fishes of 43 species from 13 families were collected by larva net in the southern branch of the Yangtze River Estuary,Hemiculter bleekeri is most abundant species,Rhinogobius giurinus,Culter alburnu,Carassius auratus,Parabramis pekinensis.In total 115 species and 32 families were collected.83 species were identified to species level.There were 34 freshwater fish,chiefly Cyprinidae,3 migratory fish,Coilia nasus,Anguilla japonica,Lateolabrax maculatus,32 estuarine fish,chiefly Gobiidae and 14 marine fish.The total number of commerical fish larvae and juveniles was 38,belonging to 24 families.6 species from Cyprinidae,4 species from Gobiidae,2 species from Clupeidae,2 species from Osmeridae,2 species from Engraulidae,2 species from Mugilidae,2 species from Sillaginidae,2 species from Sciaenidae.16 species were collected by larvae net in the southern branch of the Yangtze River Estuary.36 species were collected by seine net in the surf zone of the Yangtze River Estuary.10 species were collected in both surf zone and the southern branch of the Yangtze River Estuary: Parabramis pekinensi,Pelteobagrus fulvidraco,Siniperca chuatsi,Rhinogobius giurinus,Coilia nasus,Anguilla japonica,Lateolabrax maculatus,Acanthogobius ommaturus,Boleophthalmus pectinirostris,Cynoglossus abbreviates.The development stages of larvae and juveniles in the surf zone of the Yangtze Estuary are mostly post-flexion larvae and juvenile,few pre-flexion and flexion larvae.The developmental stages of commerical fish larvae and juveniles in the South Branch of Yangtze River Estuary were mostly pre-flexion and flexion larvae,but also some postflexion larvae and juveniles.According to the specimens of juvenile and juvenile fish collected from 2004 to 2016,the morphology of 38 commerical fish larvae and juveniles in the Yangtze River Estuary and neighboring area were observed and measured.According to the literature,morphometrics characters,the number of vertebrae or myomere,the development of fins,the distribution of pigment and the head spinations were described and drawn.The study provided main morphology characteristics to identifed different species and the methods to distinguish similar species.The study also provided basic for the identification of commerical fish larvae and juveniles in the Yangtze River Estuary and neighboring area.