Wonderful as they are, insects do not by any means exhaustthe possibilities of suitable organisms to conduct fascinating,cutting-edge, low-cost research, especially in animal behavior.Having seen how insects can be used to this end, in all theprevious articles in this series, I will now deliberately chooseexamples from studies done on vertebrates, starting with fishand navigating through the evolutionary tree of life, all theway to humans. In this article, we will see how simple, cleverexperiments can reveal that when fish fight, the outcome isnot only based on their intrinsic fighting abilities but alsoon extrinsic factors such as prior winning and losing experiences,and indeed, on a sophisticated interaction betweenintrinsic and extrinsic factors. In particular, we will studythe phenomenon of winner-effects and loser-effects and learnthat this is a near-virgin field of research waiting to be exploitedand eminently suitable for cutting-edge research at atrifling cost.