EXOTIC FISH IN EAST ANGLIAN WATERS: PORCUPINEFISH DIODON HYSTRIX & PIRANHA PYGOCENTRUS SP

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EXOTIC FISH

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OCCURRENCE OF EXOTIC FISHES IN EAST ANGLIAN WATERS: PORCUPINEFISH DIODON HYSTRIX AND PIRANHA PYGOCENTRUS SP. J. R. ELLIS Introduction The occurrence of non-native fish species and their potential effects on natural communities and ecosystems is a major concern (Copp et al., 2005a). The UK has a long history of introducing exotic fishes to its fresh waters, including fish for food (e.g. common carp Cyprinus carpio and rainbow trout Oncorhynchus mykiss), for sport fish (e.g. pikeperch Sander lucioperca and European catfish Silurus glanis), or for ornament (e.g. goldfish Carassius auratus and pumpkinseed Lepomis gibbosus). Although no fully marine, nonnative fishes have established populations in UK waters, at least one species, pikeperch, is tolerant of saline waters. In addition to human release, non-native marine fishes can also be transported by ballast water in shipping, though this is more typical for small-bodied benthic fish, such as blennies and gobies (Carlton, 1985). The introduction of non-native fish species can have negative consequences on natural ecosystems, especially if the introduced species is capable of establishing viable populations. The effects of non-native fishes can include predation on native species, resource competition and the spread of disease/parasites (Copp et al., 2005a). Hence, the deliberate release of nonnative fishes should be avoided. However, the accidental or deliberate release of exotic fish originating from the aquarist trade and home aquaria is of increasing concern in many parts of the world (Courtenay & Robins, 1973; Semmens et al., 2004; Copp et al., 2005b; Weigle et al., 2005). Here, the occurrence of two species of exotic fish in the waters of East Anglia is documented, both specimens having been released deliberately. Even though both specimens were recovered as dead individuals, these findings highlight the fact that deliberate releases of ornamental fish, such as reported for the London area (i.e. Copp et al., 2005b), appear to be taking place in East Anglia. Porcupinefish Porcupinefish Diodon hystrix Linnaeus, 1758 (Tetraodontiformes; Diodontidae) is widespread in tropical and sub-tropical waters of the Atlantic, Indian and Pacific Oceans, and in the North-East Atlantic is recorded as far north as the Iberian Peninsula (Tortonese, 1984). The family Diodontidae is represented by six genera and 19 species (Nelson, 1994). The genus Diodon is characterised by long spines that can be erected, with Diodon hystrix characterised by having spines on the caudal peduncle, dark spots on the fins and a wide head, as well as minor differences in the number of fin rays. Porcupinefish are popular in the marine aquarium trade, and whereas most species grow to maximum sizes of about 30–50 cm length, D. hystrix can grow to more than 90 cm (Tortonese, 1984). As such, porcupinefish are capable of outgrowing home aquaria, and this increases the risk that the species may be released to the wild (Copp et al., 2005a).

Trans. Suffolk Nat. Soc. 42 (2006)


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