Toxicological Effects of Waterborne Boric Acid and the Protective Role of Dietary Black Cumin (Nigella sativa L.) Oil in Nile Tilapia (Oreochromis niloticus): Hematological, Biochemical, Oxidative Stress and Histopathological Responses

This study aimed to evaluate the protective effects of dietary black cumin ( Nigella sativa L.) oil on hematological, biochemical, oxidative stress, and histopathological responses in Nile tilapia ( Oreochromis niloticus ) exposed to waterborne boric acid. After determining the 96-hour LC ₅₀ value of boric acid, the experimental design included exposure to 1/20th of this concentration. Fish were fed for 21 days with diets either containing or lacking 1% black cumin oil. At the end of the feeding trial, blood parameters, oxidative stress biomarkers, and tissue histopathology were analyzed. The group receiving black cumin oil without boric acid showed the most favorable physiological and biochemical profiles. In contrast, the group exposed to boric acid alone exhibited significant negative alterations. Importantly, fish fed black cumin oil while exposed to boric acid showed improvements across all measured parameters compared to the toxicant-only group. The findings indicate that dietary black cumin oil effectively alleviates the toxic effects of waterborne boric acid on Nile tilapia, supporting its potential use as a functional dietary additive in aquaculture.