I am absolutely certain I saw a fish identical to that in a cave in North Wales on the evening of Thursday 23rd March.
I was at the head of a group of 4 people and on "hands and knees" in a low spot. The floor under the water was silted and the fish was sat there.
I stopped and alerted everyone to it.
It was around 4-5 inches in length and (knowing almost nothing about fish) I described it as a colourless catfish (it may or may not have had a pink tinge)
It was not concerned with the presence of my hand next to it.
Sadly, as the others moved in the confined space, the silted floor was disturbed and the fish was lost to sight.
Perhaps they are not as rare as thought?
Ian