seems swimming blader issue with bloated stomach.. Do you have any previous photo of the fish when he/she was healthy and swimming.. Did you see him swimming when he started like this ? what are the water parameters? any other fish was sick before this one? any accident like over fed, Or heater issues, or anything ? he/she looks more sick and need to start the urgent treatment with medications after finding what's he going on with? poor guy!! sad to see him like this :-(