COMMUNITY STRUCTURE AND CORRELATION OF DOMINANT SPECIES IN EARLYFISH RESOURCES IN THE OUJIANG ESTUARY

In order to grasp the current status of early fish resources in the Oujiang Estuary and the correlation with major environmental factors, an analysis was conducted based on the surface horizontal trawl data and fundamental hydrological survey data collected from 25 stations within the Oujiang Estuary during spring (May), summer (August) and fall (November) of 2021. The assessment included the species dominance of fish eggs and young juvenile fishes, biodiversity and community structure characteristics. The investigation also delved into the interplay between the dominant Stolephorus spp. species and environmental factors. The results showed that a total of 8427 eggs and 40365 fishes were collected in three cruises, and 49 species were identified, belonging to 12 orders, 23 families and 39 genera, with Perciformes as the main group. The developmental stage analysis indicated a prevalence of fishes in the pre-bending stage, with predominantly marine and estuarine species. Variations in species, numbers and densities of fish eggs and larvae were observed in different seasons, with average densities ranging from 0.07 to 4.72 fish (larvae)/m³, and the highest densities in spring were 34 species, 38083 fish larvae, and 4.72 fish (larvae)/m³. The spatial distribution showed an increasing trend along the Oujiang Estuary from the inside to the outside, with a concurrent decrease in fish larvae. Biodiversity variations were notable in all seasons, with the highest diversity index (H′) and evenness index (J′) in spring, and the highest richness index (D) in summer. The dominant composition species of fish eggs and juveniles varied greatly among seasons, with side-banded small male fishes of genus Gobiidae spp., Coilia mystus linnaeus and Cynoglossus sp.1 identified as common dominants in spring, summer, and fall, respectively. The Relative Importance Index IRI showed the dominance of fishes from the genus Side-banded small males in all cruises, with the highest correlation to salinity (P<0.01) and the lowest to temperature (P<0.05). Comparisons with historical data suggested that the sea area near Beilong Island in spring is an important spawning ground for fish, and the high temperature, high salt and weak alkaline hydrological environment is more favorable for the growth and reproduction of Stolephorus spp.. These findings provide a reference basis for the conservation and management of fish resources in Oujiang estuary and the protection of the fishery ecosystem.