The ontogeny of antipredator behaviour in paradise fish larvae III. Size-related avoidance of predator models

A series of laboratory experiments examined the effect of the size of preda tor models on the behaviour of larval paradise fish Macropodus opercularis L., of different age (15 and 20 days old). In a small runway. individually tested larval paradise fish could approach a model predator of different si ze, with or without eyespots. The duration of approach, the number of fleei ngs and backings were measured. Fifteen-day-old larvae showed similar moder ate level avoidance to all models but fled more in the presence of larger m odels. The approach behaviour in 20-day-old larvae depended on the size of the model but only if it had eyespots, and Larvae Bed and backed more with increasing size of the model. However, manipulation of larval length within age category had no effect on predator avoidance. Since the recognition of the two eyespots seems to be age dependent, it is hypothesized that only l arvae older than 20 days will behave in a 'threat-sensitive' manner in the presence of predator models by avoiding larger ones. (C) 1999 The Fisheries Society of the British Isles.