Fishmeal can be totally replaced by a mixture of rapeseed meal and Chlorella meal in diets for crucian carp (Carassius auratus gibelio)

This study was conducted to investigate the effects of dietary fishmeal (FM) replacement by a mixture of rapeseed meal and Chlorella meal (RCM) on growth performance, apparent digestibility coefficients (ADCs), digestive enzymatic activities and intestinal histology of crucian carp Carassius auratus gibelioi. Five isonitrogenous diets were formulated to replace 0% (RCM0), 25% (RCM25), 50% (RCM50), 75% (RCM75), and 100% (RCM100) of protein from fishmeal with RCM respectively. Each experimental diet was randomly assigned to triplicate groups with 25 juvenile fish (initial body weight: 1.77 ± 0.04 g) per fibreglass tank for 6 weeks. With increasing substitution levels, weight gain rate, specific growth rate, feed intake and protein efficiency ratio increased, but feed conversion rate decreased. Dietary RCM substitution improved lipid content of muscle, but had no significant effect on other proximate composition of muscle and liver. ADCs of dry matter, protein, lipid, energy and the majority of amino acids increased with increasing substitution level, and digestive enzyme activities (amylase, trypsin and lipase) in intestine showed the similar trend with ADCs. Dietary RCM substitution had no significant adverse effect on intestinal histology. This study indicated that FM protein could be completely replaced by mixed protein sources (RCM) in crucian carp diets.