Many cichlid species in the shallow-shore of Lake Tanganyika suffer damage from attacks by the scale-eater Perissodus microlepis. Many prey fish engage in warning behaviors to this predator. It has been hypothesized that, if prey fish have difficulty employing such behavioral tactics, morphological defenses against scale-eating, such as hard scales, will evolve. The shrimp-eating cichlids, Altolamprologus compressiceps (Ac) and Neolamprologus fasciatus (Nf), exhibit hunting behaviors in which they remain motionless for up to 10 seconds while aiming at prey, when they are vulnerable to scale-eating predators; thus, these fish have likely evolved morphological defenses against “scale-attacks”. We tested this hypothesis in Ac and Nf, as well as three other predatory fish, Lamprologus callipterus, Lepidiolamprologus elongatus and Lep. attenuatus, that are not motionless for such a long time. Under natural conditions, Ac and Nf were rarely attacked, while the other three species were attacked frequently. When freshly killed specimens of these five species were displayed underwater in the presence of P. microlepis, Ac was rarely attacked, while Nf and the three other species were attacked frequently. Among the five fish species, the force required to tear off scales was highest for Ac, and this force was negatively correlated with the frequency of attacks on the displayed fish. These results support the hypothesis that the hard scales of Ac function as an anti-scale-attack measure, although it remains unclear why free-swimming Nf were rarely attacked while aiming at prey, despite the fact that the force required to tear off its scales was not large.
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Vol. 36 • No. 2