Effect of a variety of animal, plant and single cell-based feed ingredients on diet digestibility and digestive enzyme activity in redclaw crayfish, Cherax quadricarinatus (Von Martens 1868)

Readily available agricultural products are often considered as feed ingredients when investigating cost-effective diet formulations for aquatic organisms. We investigated the potential use of fish meal (FM), meat and bone meal (MBM), poultry meal (PM), soybean meal (SBM), canola meal (CM), lupin meal (LM) and brewer's yeast (BY) in dietary formulations for redclaw crayfish, Cherax quadricarinatus. Test ingredients were incorporated at 30% inclusion level in a commercial redclaw pellet, and used in digestibility trials where apparent digestibility coefficients (ADCs) and digestive enzyme activities were measured and correlated. High ADC values were recorded for all treatments. The SBM diet had the highest apparent digestibility for dry matter (ADMD) (84.5%), crude protein (ACPD) (94.1%) and gross energy (AGED) (91.4%), while the lowest value was obtained for the diet containing MBM (75.9% ADMD; 88.5% ACPD; 85.5% AGED). Overall, ACPD was significantly higher (P < 0.05) for diets containing plant-based ingredients (93.5%) than for animal-based ones (90.0%). Similar trends were observed when dry matter and crude protein digestibilities were compared for specific feed ingredients. Specific activities of protease, amylase, cellulase and lipase in mid gut (MG) gland extracts were also determined for redclaw fed test diets. Generally, carbohydrase and lipase activities in individuals fed plant-based diets were significantly higher than in those fed animal-based diets. A significant correlation was observed for enzyme activity and ADC values. Protease activity was negatively correlated with diet ADMD, ingredient (I) ADMD, IACPD and IAGED, while lipase activity was positively correlated with ACPD and IACPD. Amylase/protease ratio (A/P) was positively correlated with all digestibility coefficients except AGED. Based on these observations, we conclude that redclaw have the capacity to successfully utilize nutrients from a broad range of dietary ingredients including animal, single cell and in particular, plant matter in their diet. We also suggest that digestive enzyme secretions and the ratio in which they occur, play a key role in determining digestibility of nutrients by redclaw.