Shark With Pink Bulge

[tenohfive]

Someone I know from work has a silver shark with a pink bulge by its backside, and its been noticably swimming slowly. I know its not alot of info to go on but any ideas?

 

[WILDER]

Size of tank in gallons or litres.
How many fish and which type.
Water stats in ammonia, nitrite, nitrate, and ph.

Do you mean a pink lump near its backside, is the anus red and inflamed, or enlarged.

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