Astacus leptodactylus Eschscholz introduced in the Netherlands

Until the appearance, in 1970, of the American crayfish Orconectes limosus (Rafinesque, 1817) in the Netherlands, only a single species of crayfish was known here: Astacus astacus (Linnaeus, 1758). Geelen (1978a, b) provided an extensive discussion on the distribution of the two species. On 13.vi.1980 the Rijksinstituut voor Visserijonderzoek of IJmuiden (National Institution for fishery Research, RIVO) presented the RMNH a freshwater crayfish with a request for identification. The specimen was caught by a fisherman in a freshwaterpond (named IJ) near Spaarndam, NW of Haarlem, province of Noord-Holland. The pond has an open connection with the Noorzeekanaal, the mostly brackish canal that connects Amsterdam with the North Sea. The crayfish, a male with a carapace length of 49.8 mm (total length 103.6 mm) proved to belong to Astacus leptodactylus Eschscholz, 1823 (pl. 1). A month later a second specimen of the same species was caught with hook and line in the small port of Moerdijk, on the Hollands Diep, province of NoordBrabant, by Mr. A. van As of Roosendaal. This capture was reported upon in the daily newspaper Brabants Nieuwsblad of 18.vii.1980 in which also a photograph of the specimen was published. The specimen shown in the picture was definitely neither A. astacus nor O. limosus. Mr. van As, who kept the specimen alive in his aquarium, was kind enough to allow me to examine it, and there can be no doubt that it likewise belongs to A. leptodactylus. Dr. J. F. M. Geelen, University of Nijmegen, confirmed (in litt., 12.viii.1980) that these were the first records of A. leptodactylus for the Netherlands; she had expected that it would appear here sooner or later. A. leptodactylus inhabits eastern Europe (Rumenia, Bulgaria, Yugoslavia, Czecho-Slovakia, East-Germany, Poland and Russia). In many countries, for