Phenotyping stimulus evoked responses in larval zebrafish

The aim of the present study was to establish an effective method of analyzing individual variation in stimuli-evoked behavioural responses. The same genetic, environmental and experimental conditions were maintained throughout in order to limit variation. Naive larval zebrafish ages 5 and 7 days post fertilization were exposed to a water or chemical stimulus (adenosine) and observed for changes in bursting activity. Fish exposed to water demonstrated highly variable responses including increases, decreases and biphasic changes in bursting activity. Since the experimental settings were controlled, these differences between individuals may be related to fish personality. To interpret our data we applied a novel threshold based sorting protocol to each fish. Individuals were successfully grouped into 24 pre-defined behavioural response phenotypes. The phenotypes had distinct movement patterns and contained different proportions of fish. The same sorting method applied to adenosine exposed fish resulted in similar ratios of phenotypes. This suggests that solution addition as a stimulus evokes different yet replicable responses in a fish population. Comparisons within phenotypes and across treatments revealed subtle differences in activity between water and adenosine exposed fish. Adenosine treated fish had either increased or decreased bursting frequency depending on the response type. These results suggest that phenotypic separation prior to analysis enables observation of treatment differences that may have otherwise been missed. In summary, the present study demonstrates the practice of behavioural phenotyping as a successful method for analysis of individual variation in a population.