A hundred or so of these near transparent glimmerings were dancing in the stream today. When I approached, they skittered away, only to return, as though curious and readjust to the above-water-scape of light and shade. I put my hand in the water to see if they'd nibble or examine, but they kept a wary distance, with the occasional braver individual coming close before turning tail.
Above, dancing in the air not water, were a number of fire-red dragonflies. Were they parenting or predating? Probably neither.
A brief look at the British Dragonfly website suggests the 'dragonflies' might have been a particular damselfly (the large red). But they also might have been dragonflies... some kind of darter...
In any case, their young appear to have more in the way of legs than the things I saw... though I thought the things I saw had... well, finny-feelers on their undersides.
A search for tiny transparent fish in rivers in England brings up nothing useful. Except that there's a new sport - microfishing... fishing for very small fish. Freaks. Why would a huge great clumsy human want to harass very small fish???
Anyway. This post suggests that there is far more that I do not know than I know about dragon/damselflies and fish. Maybe, though, in the grand scheme of things, it really doesn't matter.
Microfishing!! Good grief :-( Maybe yours were salamander babies? https://pethelpful.com/wildlife/Waterdog-to-Tiger-Salamander