Dietary manganese requirement of stinging catfish Heteropneustes fossilis

The study was aimed to determine the optimal dietary manganese (Mn) requirement by evaluating the effects of various dietary Mn levels on the growth performance, whole-body chemical composition, bone mineralization, and haematology of juvenile stinging catfish Heteropneustes fossilis. Five isonitrogenous purified diets containing graded levels of supplemental Mn from MnSO4. H2O (0, 5, 10, 15 and 20 mg Mn kg-1) were formulated, and referred to as Mn0, Mn5, Mn10, Mn15, and Mn20, respectively. Fish (mean weight of 1.24 g) were stocked in 15 glass aquaria (40 fish per aquarium) each of 180 L water capacity. Each diet was hand-fed twice a day (9.00 and 16.00 h) to apparent satiation to triplicate groups of fish, 7 days a week for 10 weeks. Results indicated that significantly (P < 0.05) the highest % weight gain (186.65 +/- 6.59 g) and specific growth rate (1.59 +/- 0.13 % day-1) were observed in the fish fed with Mn10 diet supplemented with 10 mg Mn kg- 1 diet. The fish feed with Mn10 diet had significantly the lowest (1.80 +/- 0.16) feed conversion ratio (FCR). Incorporating dietary Mn up to 10 mg kg- 1 was reported to boost whole-body protein; however, subsequent increases in dietary Mn inclusion level did not result in any changes. The whole-body moisture and lipid contents of stinging catfish dropped significantly (P < 0.05) when fed with 10 mg kg- 1 Mn (Mn10) supplemented diet. The concentration of Mn in muscle and bone rose linearly (P < 0.05) up to the dietary intake of 10 mg Mn kg- 1 diet and then it remained stable. The amount of iron (Fe) in bone and muscle was found to decrease as dietary supplementation level of Mn increased. Increasing dietary Mn levels up to 10 mg kg- 1 was found to increase haemoglobin (Hb), red blood cells (RBC), white blood cells (WBC), and mean corpuscular haemoglobin (MCH); however, further increase in dietary Mn levels caused these values to decrease. The amount of dietary concentration between 7.99 and 10.38 mg Mn kg- 1 diet was revealed to be acceptable for culture stinging catfish by applying the second-order polynomial regression analysis. It is concluded that better growth and physiological status of stinging catfish can be ensured by using optimum Mn levels in the diet. The results of this study will also motivate further research into the dietary Mn requirements of other species.