Digestive ability of the freshwater crayfish Paranephrops zealandicus (White) (Parastacidae) and the role of microbial enzymes

SUMMARY. 1 Ingestion rate, assimilation efficiency and digestive enzyme activity were investigated in the New Zealand freshwater crayfish, Paranephrops zealandicus (White). Rates of ingestion of fresh and decaying Elodea canadensis Michx. were highly variable at 15°C and assimilation efficiency averaged 21%.
2.Hepatopancreas extracts showed enzyme activity towards each of nine substrates tested; microcrystalline cellulose (MCC), carboxymethyl cellulose (CMC), cellobiose, amylose, pectin, mannan, laminarin, chitin and'Azocoll' (a dye-collagen complex).
3. Three genera of Enterobacteriacae were isolated from digestive juices and hepatopancreas samples and microbial activity was implicated in the breakdown of MCC, laminarin and protein. Host-specific activity was not detected in the assays with MCC suggesting a solely microbial source for this enzyme.
4. Although cellulose cannot be broken down without some degree of prior conditioning, the polytrophic feeding strategy of P. zealandicus is indicated by the presence of host-specific enzymes that hydrolyse storage and structural sugars of algae, fungi and higher plants as well as animal protein.