Status quo of fish larva resources in Rugao section of Yangtze River

【Objective】 To investigate the status quo of fish larva resources in Rugao section of Yangtze River，to explore species composition，ecological types，community characteristics and spatial and temporal characteristics of fish larvae abundance，so as to provide basic data for the monitoring of fish larvae resources in the estuary of the Yangtze River.【Method】 The fish samples were collected by early fish resource survey method，and the samples were brought back to the laboratory for species identification under Olympus SZX 16 stereoscope.The cytochrome c oxidase subunit 1（COI）gene sequence molecular identification were conducted for of fish larvae of species with incomplete or uncertain morphological characteristics.Abundance，relative importance index（IRI）and community characteristic values［Margalef’ s richness index（D），Shannon-Wiener diversity index（H'），Pielou’ s evenness index（J），Simpson’ s dominance index（λ），Jaccard similarity coefficient（Cj），Cody difference index（βc）］of fish larvae of each species were calculated.【Result】 A survey on fish larva resources was conducted in the Rugao section of the Yangtze River from May to August in 2021.During this period，a total of 69355 fish larvae were collected，belonging to 6 orders，8 families，40 species，among which 9 were dominant species（IRI≥100）and 9 were common species（100>IRI≥10），accounting for 85.01% and 12.97% of the total.Fish larva abundance ranged from 1.50 to 9668.17 ind/100 m³，with an average abundance of 502.74 ind/100 m³.The ecological types of fish larvae were divided in four ways：the fish larvae were mainly sedentary fish；most of them were demersal fish；they were mainly omnivorous，followed by carnivorous；and there were more fishes that produced adhesive eggs and drifting eggs.In terms of time，fish larva abundance peaked at the end of May（1490.48 ind/100 m³），and lowered in June，showing a positive correlation with water flow variation.Spatial distribution of fish larvae was affected by habitat，river morphology and flow velocity，and the abundance in the nearshore was higher than that in the middle of the river（714.55 ind/100 m3 in the north bank，615.58 ind/100 m³ in the south bank and 290.31 ind/100 m³ in the middle of the river）.Diversity analysis showed that D，H'，J and λ were 3.50，2.33，0.63 and 0.16，respectively.【Conclusion】 Compared with previous research results from 2018 to 2020，the number of fish larvae，abundance and community diversity characteristics in Rugao section of the Yangtze River increased significantly in 2021，and the early recruitment population of fish in Rugao section recovers well.