spinosus trouble

my spinosus has been out its cave and wondering round the tank for the last 2 days then this morning its tail fin is all red at the edges and the skin on the rear half is falling off in big slimy clumps like its been sun bathing for to long
i dont think its been fighting with other fish because if anything had a go it would be scratched up big style

any advice would be most appreciated

bollocks its dead
on closer inspection when i took it out of the tank its stomach was bloated and its anus was sticking out slightly so maybe it was constapated because of over feeding (a cockle one day a algue wafer the next day) am treatin the tank with esha2000 incase it was anything the other fish might catch
i feel really guilty i think i should have put it out of its misery earlier today