Abstract

A comparative study of physiological and biochemical indices of the native European crayfish species Astacus astacus (Linnaeus) and Astacus leptodactylus Eschscholtz, and the alien American crayfish Pacifastacus leniusculus (Dana) was carried out to reveal the physiological basis of the different ecological fitness of these systematically related crayfish species in Lithuanian waterbodies. Investigations of somatic indices showed that the highest (p < 0.05) hepatopancreatic-somatic index was found in intermoult males of A. leptodactylus. The highest level (p < 0.05) of mineralisation of the carapace was determined in signal crayfish P. leniusculus. The level of proteolytic activity in the digestive tract of young-of-the-year juveniles was significantly higher (p < 0.05) in P. leniusculus when reared under similar feeding conditions as A. astacus. However, comparison of the proteolytic activity in adult crayfish revealed that in all aspects of the feeding cycle investigated a higher level (p < 0.05) of enzymatic activity was present in the hepatopancreas and the gastric fluid of A. astacus compared to P. leniusculus. Dipeptic activity was highest (p < 0.05) in the digestive tract of A. leptodactylus at various stages of the moult cycle. The highest concentrations (p < 0.05) of the steroid hormones testosterone and corticosterone which regulate processes related to growth, reproduction and adaptation to environmental changes has been found in P. leniusculus underlining the high competitiveness of this introduced species.

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