Predator recognition and anti-predator responses in the rainbowfish Melanotaenia eachamensis

Predator evasion behaviour patterns of three populations of rainbowfish (Melanotaenia eachamensis) were compared. The populations differed in the level of complexity of their natural habitats and the type and extent of predation. The predator recognition abilities of fish were assessed by exposing them to models differing in their degree of predator realism. The availability of vegetated cover and the location of the models with respect to cover were manipulated. Fish from Lake Tinaroo, a relatively open habitat containing numerous predators, showed strong changes in elective group size (EGS) in response to the different models but did not rely on cover as a place of refuge. In contrast, Dirran Creek fish originate from a small, fast-flowing, structurally complex stream lacking predatory fish species, and they showed little ability to distinguish between the different models and responded to threat by spending longer in vegetated areas. Members of the Lake Eacham captive stock increased their EGS in response to models representing low threat and with more threatening models increased the amount of time spent in vegetated regions of the arena. The contrasting reactions to predatory threat displayed by these populations highlights the need to use a number of different response indices when comparing the anti-predator responses of different fish populations. These data suggest that the level of habitat complexity as well as prior predator experience influence anti-predator responses of different fish popu-lations. Received: 2 October 1996 / Accepted after revision: 27 March 1997