Aquatics Unlimited: Articles: Fat Fish I: Obesity
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Fat Fish I: Obesity

for the week of 6/3/99

On occasion, fish are noticed to appear to balloon up, sometimes up to double their expected girth. There are several possible causes which will be addressed in future tips, but for now let's look at plain old obesity.

Do fish really get "fat?" Why not? Aquarium fish have it made: food is brought to them on a silver platter and predators are non-existent. And there's little reason to go anywhere, even if their tank is big enough to allow it. It's not hard to imagine that they could easily consume more calories than they burn off in exercise. It's as if Tarzan suddenly had to work a desk job and eat fast food, and couldn't find his way to the gym. (Hey, maybe fish do need bicycles!)

How can you tell if a fish is fat or ill? Most other causes of bloated appearance come on rather abruptly, while obesity is a gradual process, as it is in humans. Also, most other problems affect only one fish in the collection at a time, while obesity is frequently a problem for all the fish of the same species. Finally, ill fish often stop eating, while obese fish chow down as long as food's available.

What sort of fish are affected? Any fish can become obese, but it is most often a problem with large (e.g. cichlids) or active (e.g. barbs or tetras) fish kept in too small an aquarium. These fish are pre-disposed to eating large and/or frequent meals to provide for growth or activity. If the growth and activity are limited by their surroundings, but food availability isn't, they soon need to shop in the "husky" department.

Is there treatment? Until Weight Watchers develops a program for fish, aquarists will have to deal with fish obesity the old-fashioned way: less food, more exercise. Prevention and treatment are the same: feed fish sparingly, and don't skimp on the size of their tank.


"Tip of the week" appeared regularly in 1999 and 2000.

Copyright © 1999 Aquatics Unlimited
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