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Congratulations @fullabeans
You are the winner! I will send you your reward shortly.

Under the conditions you set out, I guess that fullabeans does get the reward, which is a bit spurious as they were not even close to close in their identification of this fish, which is worse than not commenting at all.

They all look so similar, but i’m yet to find a definite match. Sometimes I wonder if it’s an unidentified species.

No, it is definitely an identified species. It is an Empire Gudgeon, I have kept hundreds of them in the past. Bred most of mine myself.