Dietary Manganese Requirement of <i>Catla catla</i> Juveniles

Manganese (Mn) is an essential trace mineral hat plays a vital role in fish growth, metabolism, and antioxidant defense, yet its precise dietary requirement for Catla catla remains unclear. Therefore, this study was designed to assess the manganese (Mn) requirement and its impacts on the growth and health of Catla catla juveniles. Six experimental diets were formed by supplementing Mn from MnSO₄.H₂O at levels of 0, 5, 10, 15, 20 and 25 mg/kg, and the actual Mn values were analyzed 1.41, 6.35, 11.22, 16.31, 21.15 and 26.12 mg/kg, respectively. Fifteen juveniles (initial weight 13.84 ± 0.02 g) in 70 L capacity tank were fed each diet twice daily upto satiation for 60 days. The growth performance, feed conversion ratio (FCR) and biometric indices were increased significantly (p < 0.05) with Mn level up to 16.31 mg/kg and then plateaued. However, feed intake (FI) increased (p < 0.05) continuously with increasing Mn supplementation in the diet. Fish fed Mn supplemented diets (6.35-16.31 mg/kg) showed significantly higher (p < 0.05) dry matter, protein and fat contents in whole body. Moreover, a linear increase (p < 0.05) in the Mn absorption and Mn contents in vertebrae and whole-body was observed with Mn concentration up to 26.12 mg/kg, whereas the Mn content in the muscles, scales and kidneys peaked at 16.31 mg/kg. Antioxidant enzymes and alkaline phosphatase (ALP) activities were increased significantly (p < 0.05) with Mn level of 16.31 mg/kg in the diet, followed by stabilization. However, thiobarbituric acid reactive substances (TBARS) decreased continuously (p < 0.05) in response to Mn levels. The optimum Mn level was estimated to be 14.22-16.31 mg/kg for C. catla fingerlings. In conclusion, Mn supplementation improved growth, biometric indices, whole-body proximate composition, Mn absorption, Mn content in tissues, antioxidant enzyme activities and ALP activities in C. catla juveniles.