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Fish meal, vitamin C and fish oil are known to play essential roles in reproduction and immunity in animals. To investigate how the diet affect reproduction under the condition of reducing costs, we designed an experimental diet that decreased the ratio of fish meal with soybean meal from 1:1 to 1:1.5, and supplemented with 0.06% vitamin C and 3.8% fish oil for the crayfish, P rocambarus clarkii. After a 100-day feeding experiment, female crayfish fed the test diet had significantly greater gonadosomatic index ( GSI) compared with those fed the basal diet ( P < 0.05). At the middle stage of ovarian development, the test diet gave significantly higher trypsin-specific activity (340.94 ± 57.32 U mg−1 protein) in hepatopancreas of the crayfish than the basal diet (89.48 ± 10.01 U mg−1 protein) ( P < 0.05). However, hepatosomatic index ( HSI) was remarkably decreased for those females fed test diet ( P < 0.05). In addition, the experimental diet resulted in markedly lower superoxide dismutase ( SOD) activity and malonaldehyde ( MDA) levels, especially in the ovaries ( P < 0.01). These results suggest that dietary reduction of fish meal, supplementation of appropriate amounts of vitamin C and fish oil may promote ovary development probably by increasing digestibility, as well as by promoting transferring of nutrients from hepatopancreas to ovary and raising immunity of P . clarkii. [ABSTRACT FROM AUTHOR]