Dietary Bacillus subtilisrelieved the growth retardation, hepatic failure, and antioxidative depression induced by ochratoxin A in Thinlip Mullet (Liza ramada)

Mycotoxicosis is a severe challenge in the aquafeed industry and is involved in low productivity and high economic loss. On this occasion, available dietary supplements, including probiotics, may relieve the impacts of mycotoxicosis on the performances of aquatic animals. In this study, four test diets were prepared to test the effects of Bacillus subtilis(BS), ochratoxin A (OTA), and their mixture (BS/OTA) on the performances of Mullet (Liza ramada). Fish of similar initial weight (11.38 ± 0.24 g) were divided into four groups stocked in triplicate hapas (0.5 ×0.5 ×1 m) at 15 fish per hapa. Fish fed the control diet (without BS or OTA), BS (2 × 106CFU/g), OTA (1 mg/kg) or BS (2 × 106CFU/g) and OTA (1 mg/kg) (BS/OTA). After eight weeks, the final weight (FBW) and specific growth rate (SGR) were markedly enhanced by dietary BS and reduced by OTA contamination, while the feed conversion ratio (FCR) was meaningfully reduced by dietary BS and increased by OTA. The hemoglobin (Hb), packed cell volume (PCV), red blood cells (RBCs), and white blood cells (WBCs) were markedly lowered by OTA toxicity. Fish fed BS, or BS/OTA diets showed no significant differences with the control in terms of Hb, PCV, RBCs, and WBCs (p˃ 0.05). The BS-fed fish showed the same normal intestinal and liver structure with an improved appearance of intestinal villi. The OTA-exposed fish showed deterioration of intestinal mucosa and stunted growth of intestinal villi with severe liver vascular dilatation and congestion in addition to hepatocytes degeneration. The combination of BS with OTA alleviated the pathological effect of individual OTA on the intestinal villi, improved intestinal morphology, and restored the normal hepatic structures with mild periductal inflammatory reaction around the bile duct. The blood total protein and albumin levels were markedly increased by dietary BS and lowered by OTA. Fish fed BS/OTA diet had higher alanine aminotransferase (ALT), aspartate aminotransferase (AST), and urea than fish fed the control but lower than those contaminated with OTA. The catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD) were markedly increased by dietary BS and lowered by OTA toxicity. However, the malondialdehyde (MDA) level was decreased by dietary BS and increased by OTA toxicity. Interestingly, fish fed the control and BS/OTA diet had similar FBW, SGR, FCR, survival rates, Hb, PCV, RBCs, WBCs, creatinine, CAT, GPx, SOD, and MDA levels. In conclusion, dietary B. subtilisrelieved the negative impacts of OTA contamination via protecting fish's intestine, liver, and kidney function.