To investigate the dynamic characteristics of early fish life stages and their association with environmental factors in Xiangshan Bay, China, two surveys were conducted in the springs of 2023 and 2024 to collect fish eggs and larvae. A total of 21,221 eggs and 10,730 larvae of 23 species belonging to 5 orders and 13 families were collected. Dominant species identified from eggs included Scomberomorus niphonius, Konosirus punctatus, and Pennahia argentata, while dominant species of larvae included Engraulis japonicus, Planiliza haematocheilus, and Rhinogobius giurinus. Species diversity analysis showed that the diversity was higher in spring 2023 (H′ = 1.13) but decreased in spring 2024 due to the outbreak of dominant species (H′ = 0.86). Cluster analysis and non-metric multidimensional scaling ordination analysis revealed significant regional differentiation in the community structure of fish eggs and larvae between the springs of 2023 and 2024. Mantel test correlation and redundancy analyses indicated that temperature, salinity, dissolved oxygen, and chlorophyll-a concentration were the main environmental factors influencing the distribution of fish eggs and larvae. This study elucidates spatio-temporal patterns and environmental response mechanisms of early fish life stages in Xiangshan Bay, providing scientific support for the conservation and sustainable utilization of fishery resources in the National Fishery Germplasm Resource Reserve.

Estuaries support distinct spawning and nursery habitats for migratory fishes, yet the differential environmental response patterns between these two critical early life habitats remain poorly understood from a spatial non-stationarity perspective. Based on six ichthyoplankton surveys conducted during peak and late spawning seasons from 2018 to 2020 in the Yangtze Estuary, this study applied geographically weighted regression (GWR) models to quantify the spatially varying effects of sea surface temperature, sea surface salinity, chlorophyll-a, water depth and distance to coast on the distributions of Coilia mystus eggs and larvae. The results reveal clear divergence in both spatial pattern and environmental drivers between spawning and nursery habitats. Spawning grounds were persistently concentrated in the middle reaches of the South Branch, and shifted approximately 10 km upstream during the spring saltwater intrusion event in 2020. Nursery grounds, by contrast, formed a stable dual-core structure, with the northern core at the North Branch mouth consistently supporting higher larval densities than the southern core in the North and South Passages. Salinity was the primary limiting factor for spawning in spring, while temperature dominated in summer, and chlorophyll-a was never retained in optimal egg models. For larvae, chlorophyll-a emerged as a consistent key driver alongside salinity and temperature, and local regression coefficients spanned a wider range than those for eggs, indicating greater spatial heterogeneity in larval distribution–environment relationships. This study provides the first comparative analysis of spatially non-stationary environmental controls on spawning versus nursery habitats of C. mystus, and offers empirical support for stage-specific habitat conservation and fisheries management in the Yangtze Estuary.