Refined operation of cascade reservoirs considering fish ecological demand

•A methodology for designing refined operation strategies incorporating more ecological demands for fish spawning was proposed.•The target of continuous flow increase on an hourly scale could be accomplished via the very low regulation capacity of the Gezhouba reservoir for stimulating four major Chinese carps spawning.•Maintaining the average Dajiang and Erjiang generator output at a high outflow level could effectively increase the integrated suitable space in downstream Chinese sturgeon spawning grounds.