Ontogeny of Osmoregulation in the CrayfishAstacus leptodactylus

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Abstract
Osmoregulation was studied during the postembryonic development of Astacus leptodactylus Eschscholtz 1823 in juvenile stages 1-8 and in adults. Juveniles hatch and later stages develop in freshwater or in moderately saline waters. The time of acclimation from freshwater to a saline medium increased from early juveniles to adults. At all stages, it was longer than in comparable stages of marine crustaceans, reflecting the high impermeability of the teguments to water and ions. All stages were able to hyperisoosmoregulate. In freshwater, the ability to hyperosmoregulate was established at hatching and increased during development. The hemolymph osmolality increased from 286 mosm kg(-1) in stage 1 juveniles to 419 mosm kg(-1) in adults. All stages also hyperregulated at low salinities (7 parts per thousand and 13 parts per thousand salinity) and were osmoconformers at higher salinities up to 21 parts per thousand salinity. The lowest isosmotic salinity tended to increase with the developmental stages. The ability to osmoregulate at hatch and throughout postembryonic development is probably a key physiological adaptation in this and other freshwater crayfish.