Influence of insoluble dietary cellulose on digestive enzyme activity, feed digestibility and survival in the red claw crayfish, Cherax quadricarinatus (von Martens)

Red claw (Cherax quadricarinatus) is a freshwater crayfish species with recognized potential for aquaculture. To better understand the digestive processes and nutritional requirements of red claw, we have examined the effects of dietary cellulose on (1) digestive enzyme activity and diet digestibility and (2) survival rate, feed conversion ratio and growth performance. In the first study, a reference diet (RF) and test diets consisting of 70% RF and 30%α‐cellulose or Fuller's earth were prepared. Analysis of digestive enzyme profiles revealed that amylase and cellulase activities in midgut gland (MG) extracts were highest in the red claw fed on a diet containing 30% Fuller's earth and lowest in those fed on a diet containing 30%α‐cellulose. Supplementation of the RF diet with either 30%α‐cellulose or Fuller's earth significantly reduced apparent dry mater (ADMD) and apparent protein digestibilities (APD). In the second study, a feeding trial was conducted using diets supplemented with different levels of α‐cellulose. A major finding was that dietary cellulose levels above 12% were correlated with significant reductions in survival rate, specific growth rate and feeding efficiency. Based on these findings, we suggest that although cellulase enzymes are present in the red claw digestive system there are no apparent nutritive benefits obtained by including insoluble cellulose in diets for this species.