First record and morphometry of the non-indigenous fathead minnow Pimephales promelas (Rafinesque, 1820) (Teleostei, Cyprinidae) in Flanders (Belgium)

Pimephales promelas is widely distributed across North America. Its home area ranges from southern Chihuahua, Mexico, north to the Maritime Provinces and Great Slave Lake District of Mackenzie (Canada) and from the Rocky Mountains eastwards to the Appalachians. It has been introduced to both Atlantic and Pacific coastal drainage basins in the United States (1, 2). In Europe, reproducing populations of this non-native species have only been documented from the River Chiers in the Meuse basin in France (3). The fathead minnow (P. promelas) is a robust, somewhat laterally compressed, cylindrical cyprinid with a maximal length of 100 mm. Its overall coloration is dark olive-green or brown above with a straw-coloured to whitish belly. At the base of the caudal fin, often a narrow dark vertical bar is present. A diagnostic feature is the shortened first ray in the dorsal fin. Males generally grow larger than females and have a typical swollen black head (4, 5, 6). In 1995, the Institute for Forestry and Game Management (IBW) has made the first wild record of Pimephales promelas for Flanders (Belgium). Fish were collected using a pulsed-DC DEKA 7000 electrofishing unit with a ring anode. Three individuals were recorded in two small tributaries of the River Demer (Scheldt basin). Two specimens were captured in the Munsterbeek and a single specimen in the Zutendaalbeek. In 2001, ichthyological exploration of the Demer subbasin revealed 36 specimens of P. promelas from 7 localities in 3 different waters : Grote Gete, Melsterbeek and Cicindria (Fig. 1). The presence of P. promelas has never been recorded in other basins of Flanders, despite the numerous fish stock inventories by various research groups within the last 10 years.