No abstract

Evidence is provided that warming of the North Atlantic is responsible for the northward extensions of the ranges of warm water ¢sh species, causing increasing numbers of southern immigrant species to appear o¡ the Cornish coast of the UK. The increasing number of immigrant species is signi¢cantly correlated with temperature increases in the North Atlantic over the last 40 years.Fish immigration and Atlantic warming A.R.D. Stebbing et al. 179

Summary The crucian carp, Carassius carassius (L.), is a small fish of restricted distribution in the UK, which is probably only native to central and eastern England. The crucian carp is endemic to northern Europe. It has been widely confused with the introduced and congeneric goldfish, Carassius auratus (L.), and forms hybrids with that species and the introduced Cyprinus carpio L. The status of this fish has become confused with the presence of the congener and its hybrids, and it is now thought to be less frequent in occurrence than formerly.

The barbel was originally a fish with a relatively restricted range in the British Isles. However, despite the general environmental degradation of many British rivers, and in contrast with some native freshwater fishes, the barbel is now more widely distributed than it was a century ago. It may even be more abundant numerically.

The greater part of the literature on European fishes reports the widespread occurrence of an introduced North American catfish and identifies it as Ictalurus nebulosus. Study of the literature reporting critical determinations and of specimens from Europe and GreatBritain reveals the presence of two species, I. nebulosus and I. melas. These fishes are widely used in experimental studies, usually being obtained through aquarium-fish dealers indirectly from continental Europe. Mostly they are incorrectly identified as I. nebulosus. There is reason to believe that I. melas is the more commonly imported catfish in Britain; both species occur feral in mainland Europe.