Tackle and Tactics
Mike Ladle

Information Page

Alien species.

Where would we be without introduced fish species? Everyone knows about rainbow trout, wels catfish and zander and of course carp were introduced many years ago from the continent. I suppose in some ways we should be grateful because nowadays carp and rainbows are the mainstay of much of our freshwater fishing. Other introduced species include North American pumkinseed and largemouth bass as well as ide, bitterling and grasscarp from Europe and Asia. However, it was recently brought to my notice that there are other species lurking in our lakes and rivers which may be even more important to both the ecology and the fishing.

Last time you caught a little dace, bleak, chub or roach did you look carefully to check whether it was what you thought? In a recent issue of British Wildlife (December 2003) scientists Adrian Pinder and Rodolphe Gozlan wrote an article about two small and little-known fish that might affect all our fishing in the future. The topmouth gudgeon (from the far east) and the sunbleak (from Northern Europe), neither much bigger than the average minnow, seem now to be well established in England. Why should we care about such smallfry? After all, unless you are a matchman scratching for ounces in the depth of winter neither species is likely to provide much in the way of sport.

First things first. Both of these species soon grow to adult size and are quite unusual in breeding after their first year of life. Also, both lay their eggs in batches over the spring and summer months. Neither fish is particularly prolific but, because the males guard the eggs, which are firmly glued to water plants(SB) or stones (TMG), their chances of survival are much higher than those of most other freshwater fishes. In this way the fish may rapidly colonise any water after they have been introduced, possibly as eggs stuck to waterplants. Both are now widespread throughout much of Europe.

The sunbleak is a surface feeder and over most of its range is thought to be endangered while the topmouth gudgeon will feed at all water levels and is widely regarded as a pervasive pest. Both live in slow flowing waters but the TMG may spread into faster flows. Apparently both species were introduced as aquarium fish in Hampshire in the mid-1980s.

So, where's the problem? As I've said both can increase very rapidly. They may compete for food with other fish - particularly the young of rudd, roach or bream. On the credit side, they may also be eaten by perch, pike, eels or chub. Either or both may devour the fry, hatchlings or particularly the eggs of larger species. Apparently it is also possible that the little fish could harbour diseases.

In the case of these two little aliens it seems that the genie is now out of the bottle so the chances of getting rid of them are nil. Nevertheless we should try to avoid spreading them about any more than can be avoided. In my view, the Environment Agency and conservation bodies should be pulling out the stops to investigate how we might reduce the possible impact on native fish before it is too late.

Thanks to Adrian Pinder for the pictures.

If you have any comments or questions about fish, methods, tactics or 'what have you.'get in touch with me by sending an E-MAIL to - docladle@hotmail.com

INFORMATION SPOT

Alien Species.

Topmouth Gudgeon.

Sunbleak.