Abstract
Estuary river–lake (ERL) complex is critical for the development of ichthyoplankton, which plays an essential role in the breeding, nursing, and recruitment of freshwater fish species. In this study, different ERL sections were selected to investigate the ichthyoplankton assemblage from the Changjiang River estuary to its Hukou section between May 2018 and August 2020. During the study period, fish larvae of 40, 35, 54, and 46 fish species were sampled in the Rugao (RG), Nanjing (NJ) (nearby estuary), Anqing (AQ), and Hukou (HK) (connected river–lake) sections in the Changjiang River, respectively. Results on ichthyoplankton surveys revealed fluctuating assemblage patterns in the different river sections; larval fish species composition presented ecological habitat-dependent characteristics, which supported the importance of ERL complex for ichthyoplankton development. Furthermore, the density of fish larvae was negatively correlated with water transparency but positively correlated with water temperature, the daily rate of water level increase, and runoff in the limitative range. A generalized additive model analysis indicated that the hydrological factors significantly affecting larval fish abundance are water temperature, transparency, the daily rate of water level increase, and runoff (p < 0.05). These results also indicated that river estuaries and river–lake connected complexes are essential for ichthyoplankton recruitment and migration. In combination with the historical record, ichthyoplankton assemblage’s patterns in the Changjiang River lower reaches were preliminarily elucidated, although additional works are needed such as assessing effects on their survival and recruitment.
Highlights
The Changjiang River is the longest and one of the most human-impacted large rivers in China (Zhou et al, 2015; Zhao et al, 2021)
It can be seen that families of Cypriniformes, Perciformes, Siluriformes, and Clupeiformes were the main part of the assemblages in the sampled sections during the survey period (Supplementary Table 1)
Based on the sequential systematic surveys, this study provided an extensive content of ichthyoplankton species composition and community structure in the lower reaches of the Changjiang
Summary
The Changjiang River is the longest and one of the most human-impacted large rivers in China (Zhou et al, 2015; Zhao et al, 2021). The Changjiang River can be divided into three reaches, an upper reach above the Yichang section, a middle reach from the Yichang to the Hukou (HK) section, and a lower reach from the HK section to the East China Sea estuary (Hu et al, 2020; Zhang et al, 2020). Fishery sustainability and biodiversity conservation in the Changjiang River have faced great challenges, which include damming, isolation between lakes and rivers, construction of waterway channels, vessel navigation, water pollution, and overfishing (Fu et al, 2003; Tao et al, 2017; Liu et al, 2019; Gao et al, 2021). Based on recent survey results, the fish larvae resource of the dominant commercial fish species in the Changjiang River has been reduced sharply (Zhang et al, 2017). Renewal situations for pursuing natural resource sustainability and biodiversity conservation warrant considerable attention to achieve progress in addressing ecological issues (Bryan et al, 2018), especially for ichthyofauna in freshwater and estuarine habitats
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