if you didn't have that "UK" right there under your avatar, we would all be hollering at you for not telling us where you are, or where you saw the fish. But I am going to ask anyway... where is this fish? Looks liek an aquarium shot (and we normally dont allow ID requests of fish after you bring em home). But I think your situation might be a little different here.
You are quite right Michael, fish is in home aquarium (not mine) and purchased from lfs, who didn't know what it was! They are restricted over here and the owner now knows this, however he would like an id.
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Looks like a longear or northern longear without the red on opercular tab. If hybrid it would involve longear x pumpkinseed.
My guess is a pure longear. The great plains longears (one of the longear variants) look pretty similar. I've posted photos of a juvenile and an adult below. Yours has an ear flap that is about half way between these two.
Thanks all. I initially thought L.gibbosus-chain like markings on sides, wavy lines on dorsal; but still am unsure about the absence of the tell-tale orange/red spot-would this be a feature on adult fish only? When is this spot likely to develop?
Thanks for your patience.