Freshwater fish (or: is nothing simple)

Roach (top) and Roach-Bream hybrid (below). CC image by Jam123

People who choose fish for their collection tend to have vastly more knowledge than I do about the subject (my knowledge of fishing could be written on the back of a stamp). I admit that my only brush with fish identification (bar helping with the Environmental Health exams) is my experience of revamping and relabelling the Fish In Jars collection in the field centre. The ones from the estuary and the sea weren't too bad to identify. But when I came to specimens a previous student had collected from fresh water, things got trickier. Especially as they were all looking a bit pickled and faded.

The reason for this confusion is that some species have a habit of hybridising with others. This is apparently not uncommon, but you wouldn't know that from the identification books. They completely ignore the phenomenon, which probably says something about the psychology of people (that they prefer things to be in neat boxes, and freaky things which are neither one thing nor another become almost invisible. Oh the Fortean Times would have a field day). It was once thought that the hybrids were sterile but it now seems that some do breed (so you can have for example, Roach/Bream and Bream hybrids)... things could get out of hand when you just want to put a name to your fish.

I noticed that the Natural History Museum's name checklist doesn't flinch from the topic. But it's no use in helping you identify them.

I expect if you've got fishing experience you'll have an inkling that your specimen Isn't Quite Right, which should help.

Angling Ireland's site  has descriptions of Roach/Bream, Roach/Rudd and Rudd/Bream hybrids.

Idler's Quest also has a discussion and photos of Roach, Bream and Rudd hybrids.

There's some information on hybrid Chub here.

And so-called 'F1 Carp' are a cross between Common and Crucian carp, a deliberate and popular choice for commercial fishing lakes. There's some information on distinguishing them and other carp hybrids on the Crucian Website.

There are probably many other websites that might help, or you could add the opinions of an experienced angler into the mix too.

Failing DNA tests the ways to distinguish between ordinary species and hybrids tend to include looking at the size and shape of fins, their position, and the number of rays they contain; also the number of scales along the lateral line.

Also, they may not be present throughout the whole country - you can try looking at maps on the NBN gateway.

I can only wish you the best of luck - you might get really into this (record all your thought processes in your notebook) or if it drives you mad, you might want to include only straightforward and clear specimens in your collection.

Ancient mosaic of another hybrid - the half fish, half horse Hippocampus. You're probably unlikely to catch this though you might get an ordinary seahorse. CC image from Carole Raddato.