Effect of fish meal replacement by Chlorella meal with dietary cellulase addition on growth performance, digestive enzymatic activities, histology and myogenic genes' expression for crucian carp Carassius auratus

This study was conducted to investigate the effects of fish meal (FM) replacement by Chlorella meal (CM) with dietary cellulase supplementation on growth performance, digestive enzymatic activities, histology and myogenic genes' expression in crucian carp Carassius auratus (initial body weight: 2.90 +/- 0.02 g, mean +/- SEM). Six isonitrogenous diets were formulated at two cellulase levels (0 and 2 g kg(-1)). At each cellulase level, CM was added at three levels of 0, 533.1 and 710.8 g kg(-1) to substitute 0, 75 and 100% of dietary FM respectively. Each experimental diet was randomly assigned to triplicate groups with 25 juvenile fish per fibreglass tank for 8 weeks. Dietary CM substitution significantly increased growth, feed utilization, amylase activity and the expression of Myod, Mrf4 and Myf5, but reduced the Myog expression. Dietary cellulase addition increased hepatosomatic and viscerosomatic index, lipase activity and the expression of Mrf4, but reduced trypsin activity and the expression of Myog and Myf5. Dietary CM substitution enlarged the cell size and also caused some karyopyknosis in liver. Our results showed that CM could totally replace FM in diets; dietary cellulase supplementation at the level of 2 g kg(-1) played a subtle role in improving growth and feed utilization for crucian carp.