Why Guppies Seem to Have a Death Wish
Guppy owners know to keep the lid on their aquarium tightly sealed. Otherwise, the colorful little fish will leap to their deaths. Possibly into a chai latte. That’s where one seemingly suicidal guppy in a University of Maryland lab ended up, anyway. That latte belonged to biologist Daphne Soares’ iced chai latte, and she decided to get to the bottom of this peculiar behavior.
Usually, when fish jump they do so to escape a predator or to catch prey, Soares explains in a PLoS One paper. But for guppies, this is not the case. They jump completely unprovoked.
Puzzled, Soares and a colleague used high speed video imaging to analyze the specific movements that make up guppy jumps. The fish tended to jump by slowly backing up while using its pectoral fins (the ones on the side of its body), then strongly thrusting its body and launching itself into the air. It’s kind of like they’re backing up to get a running start. The researchers write:
The liftoff phase of the jump is fast and fish will continue with whole body thrusts and tail beats, even when out of the water. This behavior occurs when fish are in a group or in isolation.
Soares started thinking more about the conditions guppies live in in the wild. In their native mountainous streams of Trinidad, guppies manage to colonize different pools and areas of water blocked by barriers such as rocks and logs. Guppy jumping, Soares figured, may have evolved as a way to get the fish from one part of the stream into another.
Because guppy jumping events start slowly with a preparatory phase, and occur without external stimulation, we hypothesize that a jumping behavior is deliberate and has been selected as a strategy for dispersal.
So aquarium-leaping guppies don’t necessarily have a death wish, they just want to colonize the next pond—or latte—over. Unfortunately, there isn’t one there most of the time, and chai lattes aren’t exactly hospitable environments for fish.