Stream caves in the Yorkshire Dales are, as my grandma would have said, "wick" with fish. Us sump floppers come across them all the time. Trout and bullheads are most common. Eels are also fairly common, e.g, in the Dentdale caves. Lampreys (
extremely primitive fishes) are known in the Nidderdale caves. Most streams entering Dales cave systems are reasonably eutrophic so they support substantial colonies of aquatic invertebrates, which in the eyes of many fish equals food. (Note, I suspect you don't mean purely "Yorkshire" - caves in the "Yorkshire Dales" topographical area are mostly in Lancashire
and Yorkshire
and Cumbria.)
Below is an example (Cottus gobio - or bullhead) which patiently posed whilst I gently laid down a krab and fiddled with the underwater camera in the cave at the foot of Malham Cove.
The best person to respond to your query is Graham Proudlove - who wrote the book Ian Ball flagged up above. One of the chapters is about a trout captured by Dick Glover in Ingleborough Cave. (You can still buy copies direct from Graham; there's a lot in it about fish in caves.) He sometimes uses this forum; I'll email him to tell him this question has cropped up. He also wrote the book "
Cave Fishes of the World" which is essential reading if you want to delve properly into this topic.
Christine on here has also studied fish in caves whilst diving in them and will hopefully see this sooner rather than later. I think she shot some decent video of some trout in South Wales caves.
Incidentally crayfish are not unknown (Austropotamobius pallipes - the white clawed, native, variety) but of course these are invertebrates, not fish. I don't know if your interest extends that far?
There are a few caves (notably in Ireland) which open directly into the sea. These are likely to have marine fish in the first part of the caves but I think most of these caves are also resurgences so the distance which sea fishes will be able to get in will be limited by variations in the salinity of the water.
Regarding the Peak Cavern system, I have often seen trout and bullheads but only in resurgences such as the Resurgence to Swine Hole sump, or Russet Well. But further in Peak Cavern (e.g. in Buxton Water Sump, or Far Sump) I've never seen fish - and I've dived there a lot over a great many years. This is because Peak Cavern is largely fed by percolation water, unlike many Dales caves, so the streams in Peak carry very little food. (This does not apply to Speedwell Cavern, which is fed by numerous sinking streams along Rushup Edge; it'd not surprise me if fish were seen here but I can't remember ever noticing any.)
If you can tell us a bit more about why you're looking into this, folk might be able to help you in a more targeted way.
