Frightening fish isn't something you'd find on most people's daily to-do lists, but for researcher Tom Houslay, it was all in a day's work. Per the Washington Post, the evolutionary biologist at the University of Exeter gave his team the task of determining if the fish in question—in this case, 105 Trinidadian guppies—have distinct personalities, and to do so, the scientists subjected the tiny swimmers to "regular doses of fear." Those terrorizing tactics, as outlined in Houslay's study published in the Functional Ecology journal, included showing the guppies, on the other side of the tank glass, either a pulley-rigged lawn ornament heron named "Grim" or a predatory cichlid named "Big Al" every three days. The results: Some of the fish were notably braver than others. "We see quite complex strategies, more complex than we thought," Houslay tells the Post.
The Independent notes that the researchers went into the experiment to test a "simple spectrum" theory, which speculated that while some stimuli were more scary than others, the fish would basically react the same way across the board—which turned out not to be the case. The scientists used color-coded polymers under the guppies' scales to label them, then observed and timed each one as it reacted to either Grim or Big Al. Some fish stayed hidden or frozen longer than others, and their individual responses were consistent across the four-week trial. Now Houslay wants to find out if this bravery or cowardice is passed down genetically, and his team is breeding fish for the next experiment. As for the original guppies, they went back "to live happy lives again," he tells the Post. (How those frightening cichlids "talk": by peeing.)