LATERALIZATION OF PREDATOR-EVASION RESPONSE IN A TELEOST FISH (GIRARDINUS-FALCATUS)

Evidence of lateral asymmetries in the direction of turning during esc ape behaviour in a species of poeciliid fish, Girardinus falcatus, is reported. When repeatedly faced with a simulated predator (in five suc cessive sessions, spaced 7 days apart), immature Girardinus falcatus e xhibited a significant population bias to turn right on the first sess ion and a progressive bias to turn left in subsequent sessions. Mature Girardinus were then tested to check whether the shift in the directi on of turn with repeated sessions depended on maturation or habituatio n. It was found that adult Girardinus showed a slight population bias to turn right in the first session and a strong subsequent bias to tur n left after repeated sessions. The implications of these findings to our current understanding of the evolution of brain lateralization are discussed.