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

Abstract

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 'Azocoir (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.

Diet of the crayfishParanephrops zealandicusin bush and pasture streams: Insights from stable isotopes and stomach analysis

“…The S 13 C enrichment of P. zealandicus compared with known diet categories might be a result of micro-organisms in crayfish stomachs assimilating the ingested material and in turn being assimilated by the crayfish (Hicks 1997). In support of this, cellulase activity associated with bacteria has been reported in the stomach of P. zealandicus (Musgrove 1988), but the extent of enrichment is not known (Hicks 1997). Equally, the importance of terrestrial material to crayfish in these streams may be as a surface for the growth of fungi, diatoms, and bacteria (Momot 1995;Whitledge & Rabeni 1997).…”

“…), terrestrial invertebrates (whole or exoskeleton, identified to class), aquatic moss, autochthonous plant material (other than moss), aquatic invertebrates (whole or exoskeleton, other than crayfish, identified to genus), crayfish, inorganic material, and unidentified material. The percentage of the total stomach volume that each food category comprised was determined using the points method of Musgrove (1988). A 5 mm 2 grid beneath the petri dish aided in estimation of volume.…”

The presence, nature, and role of gut microflora in aquatic invertebrates: A synthesis

“…The invertebrate-microbe interaction may simply be that of predator-prey, where the invertebrate utilizes the microflora directly as a food source [33,38,39,74,91,106,111,121,156,227]. Synergism has also been documented, e.g., where invertebrates facilitate bacterial colonization by mechanically breaking down or concentrating organic material in fecal pellets [92], while microflora may precondition food material for ingestion by invertebrates [15,16,42,43,53,90,147]. Activities of invertebrates, such as bioturbation or production of bacteriocidal substances, may enhance or inhibit growth of microorganisms [4,6,26,145,210], while microbes have been reported to inhibit the activities of invertebrates, e.g., as active parasites or pathogens [1,13,19,31,32,47,65,69,70,78,94,99,154,200].…”

“…The term "resident" has often been used too loosely. Many authors suggest that bacteria are residents but do not provide conclusive evidence [147,203]. Populations of gut bacteria have been interpreted as residents simply because they are comparatively stable.…”

“…Arthropods, particularly Crustacea, have received the most attention with regard to the presence of gut microflora. Bacteria have been reported in the guts of Macrura, including prawns [44,93], shrimps [61,62,63,153,188,223], crayfish and lobsters [147,190], Brachyura [56,105,189,190,206], Isopoda [112,186,225,226], Copepoda [148,187], and Cladocera [89]. Bacteria have also been reported in the guts of Amphipoda [8,142], research being focused on deep-sea amphipods [60,110,178,192,221].…”