Measuring fear and anxiety in fish

Abstract

Fear and anxiety are indispensable defense reactions for sur- vival of animals, and have been relatively well investigated among various emotions. To reveal neural mechanisms un- derlying fear and anxiety in fish, it is essential to employ ro- bust and quantitative method to measure the level of fear and anxiety. Recently, in addition to classical comparative psychological tests, some behavioral tests incorporating etho- logical viewpoint for evaluating fish fear/anxiety have been introduced. Typical behavioral tests for measuring anxiety level include the novel environment test and light/dark pref- erence test. Classical fear conditioning and avoidance learn- ing can be used to examine the conditioned fear that is sub- jected to quantitative analysis. Innate fear response can be reproducibly evoked by exposing the fish to alarm substance. Visual and/or chemical contacts with sympatric predators also evoke fear responses in some fishes. These days, using such behavioral tests, many behavioral neuroscientific and biomedical researches have been conducted to investigate neural substrates of fear and anxiety in fishes. However, only a few species have been utilized for such researches while a great number of fish species have been adaptively radiated to various aquatic environments. Fishes showing intriguing fear/anxiety behavior might be awaiting to be discovered.