Can fish hear?

Yes! And a Stanford research group recently discovered that sounds are an integral component of the complicated mating rituals of African cichlid fish. In this species, there are two classes of males: dominant and subordinate. Dominant males defend a nest and go through a courtship dance to attract females (using visual cues: movement, color, size). Subordinate males appear more like females and do not go through all of the courtship rituals; instead, they sneak up at the last minute and fertilizes the eggs the female deposits with the dominant male. Previously, mostly because these fish are so brightly colored, it was thought that visual cues would be the most (only?) important sensory stimulants.

However, a keen observation by a postdoctoral researcher (the first author of the study) led the researchers to investigate sound as another alternative cue. Maruska observed a subordinate male zoom over to a pile of eggs from the other side of the tank–there was basically no way he could have seen the courtship displays occurring. It turns out that he heard them instead! It’s a pretty neat finding, especially since they then investigated hearing in all three classes of fish (females, dominant males, and subordinates). Females have hormone-dependent hearing, so that their hearing is focused on the same range that males produce during courtship. This type of sensitivity has been found in other animals and in other forms of communication (ie. in electric fish). But sound is hardly ever studied in fish, so this is a neat finding.

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