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In the present study, zebrafish (Danio rerio) were fed casein/gelatin-based diets containing either 19 % Bt (Bacillus thuringiensis)-maize or its parental non-Bt (nBt)-maize control for two generations (F0: sixty fish; F1: forty-two to seventy fish per treatment). The study focused on growth and reproductive performance, liver CuZn superoxide dismutase (SOD) enzyme activity, gene transcript levels targeting important cellular pathways in the liver and mid-intestine, histomorphological evaluation of the intestine, differential leucocyte counts, offspring larva swimming activity and global DNA methylation in offspring embryos. No significant effects were observed in the parental generation. The offspring were either fed the same diets as those fed to their parents (Bt–Bt or nBt–nBt) or switched from the Bt diet to the nBt diet (Bt–nBt). The Bt–Bt offspring exhibited a significantly higher body mass increase, specific growth rate and feed utilisation than fish fed the nBt–nBt diet and/or fish fed the Bt–nBt diet. Liver and mid-intestinal gene transcript levels of CuZn SOD were significantly higher in fish fed the nBt–nBt diet than in those fed the Bt–Bt diet. Liver gene transcript levels of caspase 6 were significantly lower for the nBt–nBt group than for the Bt–Bt group. Overall, enhanced growth performance was observed in fish fed the Bt diet for two generations than in those fed the nBt diet for one and two generations. Effects observed on gene biomarkers for oxidative stress and the cell cycle (apoptosis) may be related to the contamination of nBt-maize with fumonisin B1 and aflatoxin B1. In conclusion, it is suggested that Bt-maize is as safe and nutritious as its nBt control when fed to zebrafish for two generations.