How do we know? Behold, the amazing detour test:
|My drawing of the detour test, featuring Klaus.|
There have been a bunch of cool studies using this detour test that suggests that there is lateralization for aggression in a cichlid (which also depends on sex!) and in some other fish, sexual behavior, predator avoidance behavior, and much more.
One of my favorites is titled "Sex differences in the cerebral lateralization of a cichlid fish when detouring to view emotionally conditioned stimuli" (Reddon and Hurd 2009). Even though they didn't find that many significant results (only one), I found this study awesome in its design. I mean, they were emotionally conditioning fish! How do you get a fish emotional? Show it a fishstick?
Here's how they did it. They conditioned convict cichlids to associate an object with either food (positive emotional valence) or a chemical alarm cue (negative emotional valence). The objects they used were probably just lying around the lab, but they seemed to work well for their purpose: a blue pipette tip box and a yellow tennis ball.
The conditioned stimuli.
Then they gave the fish a detour test with the emotionally conditioned stimulus on the other side of the barrier. Their fish didn't seem to have a preferred side overall, regardless of whether the stimulus was positive or negative. However they did find an interaction between sex and emotional valence on lateralization: males were more lateralized in response to the negative stimulus while females were more lateralized in response to the positive stimulus. However, whether the lateralization was to the left or the right depended on the individual.
So unlike other fish, where lateralization is consistent within a population and is genetically based, it looks like convict cichlids are lateralized at the individual level. The authors don't come up with an explanation for the sex differences that they found, although they do mention that convict cichlids are biparental and males and females typically have sex-specific parental roles. The males primarily defend the offspring from intruders will the females stay close to the offspring and nurture them. Perhaps males have a specialized center on one side of their brain that responds to alarm cues, in order to respond better to attacks from predators?