Anemia is a heart and blood vessel condition which is recognized by the low number of red blood cells found in the animal. It can affect many types of fishes, so be observant of your pet and take your animal to the veterinarian if anemia is suspected.
The most common symptom -- which is also quite visible -- is abnormally pale gills in your fish.
Fishes can have anemia due to many reasons; among them:
The blood that is drained by the leeches causes anemia in fishes. They can also introduce other parasites into the fish's blood stream. Usually, aquariums and fishponds become infested with leeches because there is an infected plant or animal in the environment.
A condition of the blood in which normal red blood cell counts or hemoglobin are lacking.