Learning and Memory in Juvenile Zebrafish: What makes the Difference Population or Rearing Environment?
The ability to learn and remember about the surrounding environment is crucial for the survival of organisms in their natural habitats. Adults of numerous fish species have been shown to display sophisticated behaviour related to learning and memory. This study deals with testing learning abilities among juveniles (10 wks old) of zebrafish (Danio rerio) through a simple task of finding food. We compared the performance of juveniles from two populations, a wild collected from a natural habitat and an aquarium bred purchased from a pet shop, reared in bare environment (lacking visual cues) Additionally, we also tested the effect of early habitat enrichment on the performance among juveniles of the aquarium bred population. The experiments involved training fishes to solve a simple maze (with a food reward at the end) and testing their memory. Learning was measured based on the time taken to complete the task (performance time) of finding food in the maze arena across repeated trials. Our results showed that juveniles from the two populations possessed significantly different learning abilities. There were population differences in exploratory tendency and time taken to accomplish the task. However, when memory was tested based on performance time between training and test day, individuals (from both populations) were found to be poor at memorizing learnt tasks. On the other hand, juveniles (belonging to aquarium bred population) reared in spatially complex environments displayed higher rates of learning and were capable of remembering learnt tasks better than their counterparts from bare environments. This study thus demonstrates the importance of rearing conditions and natural ecology in ontogenetic development of learning and memory functions among zebrafish.