Aquatics Unlimited: Articles: If the Fish Fits...
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If the Fish Fits...

for the week of 7/9/98

One of the more obvious clues to whether or not fish will mix is relative size. Given the opportunity, most fish have no aversion to gulping down a smaller tankmate. In fact, the general rule of thumb is:

"If it fits in the mouth, it goes in the mouth!"

This shouldn't be confused with being "aggressive;" gobbling up other fish is a very normal pasttime for even the most peaceful species. On the other hand, from the aquarist's point of view, the result is the same: lost fish.

Sometimes the size difference alone should be enough to warn of a problem: a 10" oscar probably shouldn't go with any 2" fish. But other fish are a little more sneaky: clown knives, arawanas, African clawed frogs, leaf fish and garfish have much larger mouths than it at first appears. Some of the long-whiskered catfish, like pictus (false angelicus), shovelnose cats, channel cats and hi-fin bull sharks (a.k.a. Columbian sharks) are sometimes purchased as "scavengers," but are actually rather efficient predators. Many of these hunters not only have pretty large mouths, but also feed at night, when many of the other fish lie asleep at the bottom.

A few fish are also prone to becoming gulp-ees. Neon tetras probably head the list, since they are often purchased at a very small size, stick out like a sore thumb, have that nice, easy-to-swallow torpedo shape, aren't particularly quick, and sleep absolutely still at the bottom of the tank. Some of the others small tetras, including glo-lites and silver tips, fall into the same trap.

A particularly tragic situation often involves a large fish attempting to swallow a small Corydoras catfish. The catfish spreads his sharp spine-like fins on the way down and gets stuck. Only a rather gruesome surgery will prevent the loss of both fish.

Submitted by: Jim Kostich


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

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