Size structure, relative growth and sanitary condition of a crayfish population (Austropotamobius pallipes) living in rocky pools (Crustacea, Decapoda) Mario Mori, Sebastiano Salvidio and Paolo Cresta Mori, M, S. Salvidio & P. Cresta (1998): Size structure, relative growth and sanitary condition of a crayfish population (Austropotamobius pallipes) living in rocky pools (Crustacea, Decapoda). -Spixiana 21/2: 135-144 Bio-ecological aspects of a crayfish population inhabiting two rocky pools in the Carpasina stream (Liguria Region, N.W. Italy) were investigated per three years. A different spatial distribution between young and adult individuals was ob-served: juveniles were found under stones in shallow water, while large individuals were commonly found in deep water and in burrows present at the bottom of the pools. Length-frequency analyses showed that males are bigger than females. The sex-ratio was estimated at 1:1. Morphological variations related to sexual maturity were analysed in both sexes. Size at sexual maturity, based on allometric growth of the abdomen and chela width, was estimated at approximately 19 mm CL for both sexes. The male chelae, however, showed a further step at about 28 mm CL, indicating the existence of one third kind of male. The adaptative value of the three different kinds of males was discussed in terms of phisiological and morphological efficiency. Morphological analysis of the chelae indicated that both sexes begin their life as homochelids, but in the course of the life cycle they may lose their chelae. This seem to be related to the frequent intraspecific aggressions due to the limited space that the rocky pools offer to the species. A scarce number of crayfish was found affected both by pathologies than by branchiobdellids. Mario Mori, Istituto di Anatomia Comparata, Universitä di Genova, Viale Bene-detto XV 5, 1-16132 Genova, Italia. Sebastiano Salvidio, Istituto di Zoologia, Universitä di Genova, Via Balbi 5, 1-16126 Genova, Italia. Paolo Cresta, Ufficio Parchi, Provincia di Savona, Via Sormano 12, 1-17100, Savona, Italia. Introduction The biology of different European populations of Austropotamobius pallipes (Lereboullet) has been well studied (see for a general review Alderman & Polglase 1988, Laurent 1988, Lowery 1988). On the contrary, in Italy little has been done on the biology of A. pallipes (Ninni 1865, Mazzarelli 1903, Vinciguerra 1899, Supino 1925), nevertheless there has been a recent interest on this species (Mori et al. 1988, 1991, Specchi et al. 1991, De Luise 1991, Salvidio et al. 1993). In Liguria (north-western Italian administrative Region) the freshwater crayfish populations are still widespread both in Alpine and Apennine water courses (Salvidio et al. 1993). In this region the 135
Size structure, relative growth and sanitary condition of a crayfish population (Austropotamobius pallipes) living in rocky pools (Crustacea, Decapoda)
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