Upsidedown Catfish
Topic: Biology
Got into an interesting conversation with "P" about upside-down catfish and the how evolution may (or may not) have selected this trait.

Here's an email that P sent to me ... enjoy:

"This Catfish IS Upside Down!"

"...why they swim upside down. The reason is quite simple: it's easier to eat that way!" "Food on top of the water or under logs is much easier acquired by a fish floating upside down with it's mouth fully directed toward the food!" "...it is speculated that when food became scarce on the bottom (where most catfish eat), some species inverted (swam upside down) to take advantage of a food supply that was available at the surface. As the catfish acquired neutral buoyancy, it became more difficult to resist that upside down force. In order to save energy, the catfish gave in to the upside down swimming!"

"Some scientists believe the upside down catfish took up inverted swimming as a means of protection. The theory is that because mid-water predators usually attack from below, the upside down catfish is better able to see the imminent attack, enhancing their chance of survival."

"Another oddity, which is attributed to the inverted swimming, is the fact that the upside down catfish's belly is darker than the rest of the fish. Most fish have a lighter underside, a feature developed by them in order to escape detection from predators lurking beneath them. The lighter underside against the light water makes for a less obvious target. However, the upside down catfish has a reversal of the normal shading."

"In the wild, upside down catfish are found in huge shoals of several thousand fish."

"... "If they die, do they float right side up?" The answer: surprisingly not! Belly up like other fish, like they have spent their entire lives!"

Upside-down Catfish Site
http://www.aquafriend.com/modules.php?op=modload&name=News&file=article&sid=41&mode=thread&order=0&thold=0