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Half Black Oscar


Dear Aquaworld,

Half Black Oscar.

South American cichlids like this Oscar (Astronotus ocellatus) can cause an injury to themselves in the aquarium that can cause the half black condition above.

I have an Oscar that is app. 12" long. He is in a 55 gallon tank filtered with a Cascade filter rated for a100 gallons.  I 'm doing 50%water changes twice a week.  I am moving him into a my 75 gallon tank.  He is kept by himself since he always seems happier that way, and will be kept by himself in his new tank.  I never feed him feeder fish, only pellets, krill, and shrimp.

Here is the problem--A few weeks ago I noticed a darkened area on his upper back.  I thought he had injured himself possibly on a rock since he loves to scoop up gravel an spit it out and sometimes gets a little wild doing this.  The area got larger and now it is as if you drew a line from the top of his back down to his stomach area and it is very dark from there back to his tail.  He almost looks as if he is halfway black and the other half , from head to middle, is a normal Oscar color.  This is only on one side.  His other side is the normal Oscar colors.

He acts like he feels fine and eats normal .

I have tried to research this in books, websites and various fish forums and nothing fits this description.  All I have ever found is information on black spot which only mentions black spots appearing and his is solid from half of his body back to his tail.

If you could possibly give me any information or any ideas where I could find information on what this could be, I would greatly appreciate it.  I am afraid this might be something serious even though his seems fine now.

Thank you,

Belton,TX USA


Dear Karen,

Your assumption is correct.  I have seen this condition in discus, and it is widely accepted that it is caused by the fish banging into an object in the tank or the side of the aquarium.  It is generally accepted that the condition is an injury to the nervous system that causes the half black coloration.  In my experience, this is not a permanent condition, and usually in a week or two, the fish's normal coloration will come back.

Tony Griffitts

Published - 20070208