LAUSR

Abstract Currently, the use of herbs and phytogenic compound formulations in fish diets plays a vital role in the prevention of several fungal infections in farmed fish. Hence, this study was designed to inspect the ameliorative effect of Rosemary (Rosmarinus officinalis)-supplemented diets on aflatoxin B1 (AFB1) toxicity in terms of the performance, residual AFB1 concentration in tissue, whole-body composition, hepatosomatic index, mortality rate, serum biochemical parameters, antioxidative enzymes, immunity parameters and liver histopathology of Oreochromis niloticus. Two hundred and twenty-five randomly distributed healthy fish with a mean weight of 16.36 ± 0.048 g were divided into five diverse groups. Each group of fish was stocked into three aquaria, each containing 15 fish. The control group was fed a basal diet (T1, without AFB1) while T2 to T5 were supplemented with 2.5 mg AFB1 kg−1 diet and 0, 0.1%, 0.25% and 0.5% Rosemary respectively. The results showed that fish fed Rosemary supplemented diets exhibited significant enhancement of growth performance, crude protein levels, feed utilization, AFB1 residue levels and mortality rates compared with the T2 group. Additionally, supplementation of diets with 0.5% Rosemary kg−1 diet reduced the harmful effects of AFB1 on liver and kidney function (T2). The total protein levels were significantly improved in all Rosemary supplemented groups. The antioxidant activity and innate immunity status were significantly improved by high level of Rosemary. All liver histopathological signs were significantly enhanced to normal level upon treatment with 0.25–0.5% Rosemary. In conclusion, diets supplemented with 0.5% Rosemary reduced the harmful effects of AFB1 in terms of growth, innate immunity and antioxidant activity on Nile Tilapia.