Preferential Behaviour of Sarotherodon (Oreochromis) Mossambicus (Pisces: Cichlidae) Fry To Maternal Models and Its Relevance To the Concept of Imprinting

Abstract

The effect of previous exposure on the later preferential responsiveness of Sarotherodon mossambicus fry to maternal models was investigated. All fry were removed from their mother's mouth as eggs and hatched and reared under artificial conditions so that they were never exposed to natural maternal stimuli. In all experimental groups fry were exposed to a maternal model on day 10 post-hatching (the first day they are normally released from the mother's mouth) and tested 24 h later for their preferential responsiveness toward two models. In Experiment I separate groups of fry were exposed on day 10 to one of two maternal models of intermediate innate attractiveness. Control fry exhibited no preferential behaviour on day 11 while all groups of experimental fry responded preferentially to the same ('split') model, regardless of the model to which they had been previously exposed. In Experiment II fry exposed for 15 or 60 min on day 10 responded preferentially to a potentially supernormal 'black pit' model as opposed to the 'split' model, again regardless of the model to which they had been previously exposed. In Experiment III groups of fry were exposed to one of two 'preserved female fish' models which differed in the degree of contrast between their broody colouration and the background colouration of the fish; virtually no preferential behaviour was exhibited by these fry. The results showed that after fry have been exposed to maternal stimuli they will then respond preferentially to whichever model forms a closer match with their initial perceptual schema of the broody mother. All experimental groups of fry in Experiment I responded preferentially to the 'split' model, regardless of which model they had previously been exposed to; the same pattern emerged in Experiment II. The fry failed to respond preferentially in Experiment III possibly because they could not discriminate between the two models or because both models fit their initial perceptual schema equally well. It was concluded that while social bond formation in S. mossambicus fry is affected by early experience, there are stronger innate constraints on the process than would be expected from traditional studies of imprinting.