Fish with white flashes?

Fish with white flashes?

Observation - Fish with white flashes? - UK and Ireland. Description: This fish (one of several) appears to be displaying to other similar fishes in the vicinity (not in this image) . . They were about a quarter of the length of an apparently mature grayling nearby - about 5-8cm long. there was a slightly larger salmon par

This fish (one of several) appears to be displaying to other similar fishes in the vicinity (not in this image) . .
They were about a quarter of the length of an apparently mature grayling nearby - about 5-8cm long. there was a slightly larger salmon parr nearby as well. The white flashes were symmetrical on several of the fishes and were what originally caught my eye.
The River Itchen was very clear at this point. The weather was hazy sunshine.
I have several images taken at the same time.