Abstract: To understand the overall status of early stage fish resources in the Songzi River in the middle reaches of the Yangtze River and to explore the impact of hydrological processes on these resources, a survey of early stage fish resources was conducted from May to July 2022 in the Songzi River section. The results showed that fish populations concentrated their spawning activity by the end of June, with a decrease in egg numbers in July and a significant increase in fry numbers. Cross-analysis of the impact of hydrological processes on fish spawning revealed that changes in egg numbers preceded changes in flow by 0 to 2 days; fry numbers, on the other hand, showed a significant lagged correlation with flow (3 to 7 days). During the survey period, changes in egg numbers exhibited no significant lagged correlation with water temperature, whereas fry numbers displayed a significant lagged correlation with temperature. Using Granger causality analysis to investigate the causal relationship between hydrological processes and fish spawning, it was found that flow and water temperature had no significant causal relationship with changes in egg numbers, but did show a significant causal relationship with changes in fry numbers. Specifically, flow levels at 3 to 7 days prior had a stronger correlation with changes in fry numbers, and water temperature at 2 days prior exhibited a significant causal relationship with fry numbers. Further analysis, considering the concurrent operation of the Three Gorges Reservoir (TGR) in the upper Yangtze River, indicated that the ecological regulation of the TGR was an important factor affecting changes in early stage fish resources in the Songzi River. This regulation not only supported fish spawning in the Yangtze River, but also played a positive role in supplementing fish resources in Dongting Lake connected to the Songzi River.