How to Make Your Fish Work for You: Tips from Ethology and Ecology for Finding Appropriate Unconditioned Stimuli for Learning Studies with Zebrafish

A key requirement of associative learning studies is the ability to motivate the subject to acquire memory of the conditioned stimulus–unconditioned stimulus (CS–US) association. Although zebrafish have been found capable of acquiring CS–US associative memory, in many studies, the fish failed to learn. One reason for the failure, I argue in this perspective article, is that we do not yet know how to motivate zebrafish. I illustrate this problem using examples, and offer some solutions, based upon results obtained in my own laboratory for appetitive associative learning tasks for zebrafish. I highlight the value of considering the ethology and ecology of the zebrafish. I discuss why food may have been an ineffective US for zebrafish. I provide examples for how to improve the rewarding properties of food based upon the foraging behaviour of zebrafish in nature. I discuss the efforts to identify alternative USs, including the sight of conspecifics or the presence of other ecologically relevant stimuli. I theorize about conflicting motivators in zebrafish learning studies, including the effect of human handling versus that of experimenter-controlled USs. I conclude that systematic analyses of different USs are needed, along with detailed studies on how they may be optimized for the analysis of learning and memory in zebrafish.