Weird Microgravity Tests: Dropping Fish 360 Feet

By Wesley Fenlon

It turns out that most fish find microgravity confusing, but catfish? They play it cool.

If there's one place fish feel especially out of place, it's probably falling through the air several hundred feet above ground or water. Unfortunately for some fish in Germany, that's exactly where they found themselves--falling about 360 feet through a towering hollow tube used as a testing ground for dropping things. Scientists can go to Bremen, Germany to study the effects of gravity and weightlessness as they fall inside an enclosed space. The fish were there to serve a special purpose: They were standing in for astronauts.

Gizmodo writes that a pair of zoologists named R.H. Anken and R. Hilbig used fish as models to test the effects of microgravity. Studying how microgravity affects humans is more difficult and more expensive. So why not just throw a fish down 36 stories?

Photo credit: Bremen Tourism

"Anken and Hilbig point out, previous experiments performed elsewhere had already shown that fish 'reveal motion sickness"'when they 'transition from 1g to microgravity,' writes Gizmodo. "They thus did the next most obvious thing—what any of us would have done—they rigged a 'camcorder-equipped centrifuge' and they started dropping fish."

After their initial study with small fish, the zoologists went back a second time with catfish in hand. Catfish normally swim upside down, so how would they react to swimming in microgravity? While it may be funnier to imagine the fish flopping about in the air during their fall, they were actually in small capsules containing water. And the catfish study produced very different results.

The findings are summed up in this abstract of Anken's and Hilbig's paper:

"The catfish...often shows a unique swimming behaviour in being oriented upside-down. When swimming near a (e.g., vertical) substrate, however, the animals orient themselves with their ventral side towards this substrate. This tendency is called ventral substrate response (VSR). The VSR does not only override the upside-down swimming behaviour but also the dorsal light response and the ventral light response. In the course of an earlier drop-tower experiment performed at ZARM (Bremen, Germany) using cichlid fish, we had observed that about 90% of the animals revealed sensorimotor disorders (kinetotic swimming) due to the almost complete lack of gravity as a cue for orientation. In order to further assess the importance of the VSR for postural control in [catfish] when being located near a substrate, we subjected catfish in relatively small chambers to drop-tower flights. In contrast to our results regarding cichlid fish, [catfish] showed no kinetotic behaviour. This clearly suggests that the VSR overrides even vestibular input and possibly represents the most important single behavioural response in this species."

Catfish: Too cool for microgravity.