PhD students Dominique Roche and Sandra Binning are studying the behaviour of Anilocra parasites, which commonly attach just above one eye of coral reef fish. The pair has previously shown that the parasites affect fish by creating drag at high speed, not by sucking too much blood (AS, March 2013, p.7).
Now they have found that the parasites change the fishes’ preferences when it comes to turning at a T-intersection. “The population as a whole didn’t show a preference to turn one way or the other,” says Roche. “However, at an individual level, some fish showed a turning preference, with parasitised fish showing a much stronger preference than their unparasitised counterparts. If they have a parasite, they definitely choose a side.”
It might be expected that any turning preference would relate to the side on which the parasite attached, but this did not occur. While fish with parasites were individually consistent in their preferences, some turned towards the side with the parasite while some turned away. Parasite removal returned fish to their state before attachment.
Roche and Binning have an explanation for the apparently curious behaviour. “Having a preferred side gives the fish an advantage,” Roche says. “Lateralised fish are quicker at responding to threats.
“We’ve shown previously that parasitised fish swim slower than unparasitised fish...
