Their a chiclid a ram I think their called maybe rainbow and well yeah euthanizing deformed fish is the best thing to do the fish its deformed which can lead to sickness and may pass it on to you other fish in your tank not to mention it will struggle to survive and most likely is in pain but if you still decide to keep it make sure it doesn't breed these things are genetics are that last thing you want is to encourage a deformity in any type of fish