Dietary manganese requirement of juvenile yellow catfish Pelteobagrus fulvidraco, and effects on whole body mineral composition and hepatic intermediary metabolism

Abstract

The present study was conducted to determine dietary manganese (Mn) requirement for juvenile yellow catfish Pelteobagrus fulvidraco and evaluate the effect of dietary Mn levels on growth performance, whole body mineral composition and hepatic intermediary metabolism for this fish species. The six experimental diets were formulated to contain the graded levels of MnSO 4·H 2O (0, 3, 6, 12, 24 and 48 mg Mn kg − 1 diet, respectively), providing the actual dietary Mn values of 3.1 (control), 4.2, 5.3, 6.9, 12.0 and 19.5 mg kg − 1 diet, respectively. Each diet was assigned to three replicate groups of yellow catfish (initial body weight: 4.00 ± 0.08, means ± SD) for 8 weeks. Percent weight gain (WG) increased with increasing dietary Mn levels from 3.1 to 5.3 mg kg − 1 diet and then plateaued above these levels. The lowest protein efficiency ratio (PER), and the highest feed conversion rate (FCR) were observed in fish fed the control diet and showed no significant differences among the other treatments. Dietary Mn supplementation did not significantly influence moisture, protein and ash contents in whole body, but whole body lipid content was the lowest for fish fed the 12.0 and 19.5 mg Mn kg − 1 diets. Condition factor and hepatosomatic index were observed to be the highest for fish fed the control diet. For whole body mineral composition, increasing Mn content, and declining calcium, phosphorus and iron contents were observed in fish fed the diets containing increasing Mn levels. For hepatic enzymatic activities, the Mn-SOD activities were observed to be the highest in fish fed the diets containing 5.3 and 6.9 mg Mn kg − 1 , and the lowest for fish fed the control diet. Lactate dehydrogenase activity declined with increasing dietary Mn level from 3.1 to 5.3 mg kg − 1 diet, and then increased with dietary Mn level from 5.3 to 19.5 mg kg − 1 diet. Hepatic lipase activity was observed to be the highest for fish fed the diet containing 12.0 mg Mn kg − 1 and showed no significant differences among the treatments. Succinate dehydrogenase, malic dehydrogenase and lipoprotein lipase activities showed no significant differences among the treatments ( P > 0.05). Analysis by the broken-line regression of WG, PER and hepatic Mn-SOD activity indicated that the optimal dietary Mn requirements in juvenile yellow catfish were 5.5, 5.6 and 6.4 mg kg − 1 diet, respectively.