Social facilitation of learning in mixed-species schools of common carp Cyprinus carpio L. and Nile tilapia Oreochromis niloticus (L.)

The process of learning to associate a visual cue with food was studied in groups of common carp Cyprinus carpio and Nile tilapia Oreochromis niloticus by means of a classical conditioning paradigm. In the first phase of the study, fishes were conditioned in either single-species or mixed-species groups to associate a blinking blue light with food. In the second phase, group composition was altered so that only single species were reconditioned, composed of individuals previously paired with the same or the other species. In the first phase, in the single-species groups, Nile tilapia rapidly formed an association between the visual cue and food, whereas common carp failed to do so. In mixed-species groups, both Nile tilapia and common carp associated a visual cue with food. In the second phase of the study, Nile tilapia retained that ability irrespective of whether they had previously been trained in single-species or mixed-species groups, common carp previously trained with Nile tilapia, were not repelled by the blinking blue light and gradually approached it from a distance, whereas common carp previously trained in homogenous groups continued to be repelled by the blinking light. Fish arrivals and departures from the feeding zones as well as fish position in the testing apparatus were analysed and contrasted in single-species and mixed-species groups outside the training sessions, revealing mutual impacts of one species on the other in mixed-species groups. The findings of this study demonstrated interspecific social facilitation of learning to associate a visual cue with food.