Dietary non-protein energy sources:growth,physiology and biochemisty by the juvenile Australian redclaw crayfish,Cherax quadricarinatus(Von Martens)

A growth experiment was conducted to determine the optimal carbohydrate-to-lipid(CHO∶L)ratio for juvenile Australian redclaw crayfish［initial weight(1.72?0.01) g(mean?SD)］cultured in indoor recirculating aquaculture system.Five isonitrogenous［(31.130?0.004) g/kg］and around isoenergetic［(17.490?0.396) MJ/kg］diets with dietary CHO∶L ratios are 10.75∶1,4.81∶1,2.66∶1,1.52∶1 and 0.87∶1,were fed twice a day to apparent satiation.Over 8-week growth trial,the best final weight,weight gain,specific growth rate and feed conversion ratio value(P<0.05)were observed in redclaw crayfish fed diets with a CHO∶L ratio of 2.66∶1.Redclaw crayfish fed either the lowest(0.87∶1)or highest(10.75∶1)CHO∶L ratio tended to produce lower growth and poorer feed conversion ratio.Dietary lipid levels was 40-145 g/kg,the lipase and alkaline phosphatase activities were stimulated by elevated levels of dietary lipid.However,the activities of hexokinase and pyruvate kinase showed opposite trend.The pepsin and intestine amylase activities were significantly(P<0.01)affected by CHO∶L ratios.The higher activity of pepsin were observed when the CHO∶L were 2.66∶1 and 1.52∶1(P<0.05).The intestine amylase activity was significantly increased(P<0.01)as dietary CHO levels(156.3-360.4 g/kg)increased.Based on a second-order polynomial regression analysis of WG against dietary carbohydrate and lipid levels,growth maximum was observed when the dietary carbohydrate and lipid levels were 268.82 g/kg and 122.20 g/kg,corresponding to a CHO∶L ratio of 2.20∶1.These results indicated that the utilization of dietary lipid and carbohydrate was moderate in redclaw crayfish and the preferential utilization of carbohydrate was higher than that of lipid.