COMMUNITY CHARACTERISTICS OF LARVAE AND JUVENILE FISH IN HUKOU SECTION OF THE YANGTZE RIVER IN SPRING AND SUMMER

Hukou section, the connection between the Yangtze River and Poyang Lake for the migration route of many fish species, plays a vital role in the proliferation of fish. A systematic investigation on larval and juvenile fish resources were conducted during the fish breeding period in the Hukou section from May to August 2016. The community structure, dominant species, fish density, time-space distribution and their relationships with environmental factors in Hukou section were studied during the continuous 88-day investigation. A total of 39 larvae and juvenile taxonomic groups including 7 orders and 12 families were identified. Among them, 37 were identified to species level, one was identified to subfamily, and one was identified to family. Hemiculter bleekeri is the first dominant species and other dominant species are Gobiidae, Parabramis pekinensis, Pseudolaubuca sinensis. The larval and juvenile fish density reached its peak level on July 1 with 1230.77 ind./100 m³. The overall fish density showed a trend of decreasing volatility from July 1 to August 15. The cluster analysis divided 6 periods into 2 groups: Late May to early July in group Ⅰand late July to early August in group Ⅱ. Hemiculter bleekeri, Culter alburnus, Coilia nasus, etc. peaked in late June and Parabramis pekinensis, four famous domestic fishes, Siniperca chuatsi, etc. peaked in early July. The density of larval and juvenile fish on the south and north sides of the section were higher than that of the center section. Redundancy analysis (RDA) found that water temperature, transparency, and flow are the main environmental factors affecting the community structure of larval and juvenile fish. Correlation analysis showed highly significant correlation between water level and larval and juvenile fish density (P<0.01). This study indicates a large amount of fishes of early life history in Hukou section. The community structure of larval and juvenile fish is dominated by middle and small-sized fishes, and the proportion of river-lake migratory fishes are relatively high. Larval and juvenile fish have different adaptation characteristics to various environmental conditions. The species showed different degrees of positive and negative correlations with water temperature, transparency and flow. The results provide the scientific basis for the protection strategy of fisheries resource in the middle-lower reaches of the Yangtze River.