The ontogeny of antipredator behavior in paradise fish larvae (Macropodus opercularis) IV. The effect of exposure to siblings.
Twenty-five-day-old larval paradise fish show less avoidance behavior toward a model predator than 20-day-old fish larvae. Laboratory experiments tested two possible hypotheses: The decrease of avoidance behavior is the result of (a) change in the size ratio of larvae/model, or (b) experience with larval siblings. Larval paradise fish did not show greater avoidance of larger models or models with larger eyespots. However, if isolated for 3 days, the antipredator behavior of 25-day-old larvae became similar to younger ones. In further experiments, we raised the larvae in a larger holding tank in order to decrease the rate of encounters among conspecifics. In line with our assumptions, these larvae also showed enhanced avoidance toward a model predator. In sum, our experiments revealed that the continuous exposure to conspecific larvae was the main cause for the reduced antipredator behavior toward models. To account for our results, we suggest that larvae of nonschooling paradise fish habituate to the continuous presence of larval conspecifics and, as a result, they show decreased avoidance to the model predator. We hypothesize that this habituation process might not work in other fish species that show early schooling behavior in their development. In other words, they would not generalize the experience of conspecifics to potential predators.