Strange ill-looking behaviour in Oscar Cichlid

Question
My Oscar is fairly juvenile and is about 2-3 inches long. Recently i found him floating (head downwards) in a plant and so assuming he had died tried to remove him, but fortunately he was still alive. However he cannot swim properly and is often lying on the floor of the tank. I have seen this before and it often results in death but this has been going on for a couple of weeks?? I checked the water quality and it is perfect, as well as checking for any common symptoms such as white spot ect. As well as the Hole in the Head disease but can see no evidence of any of this. I have recently introduced a very large pearl gourami into the tank, and that seems to be when it all started but he is not aggressive at all. My tank is about 50 gallons or about 220 litres. Can you give me any advice?

Answer
Hi James,
 The fact that you do not see the pearl gourami attack the oscar doesn't mean that he doesn't do it. In fact, I would strongly suspect that is what is going on.  

-- Ron
  rcoleman@cichlidresearch.com
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