Zebrafish (Danio rerio) movement in addressing stress to conflicting stimuli, foods and predators

• Individual specificity was observed according to source of conflicting stimuli.
• Primary affectedness quantified test organism’s positional sensitivity to stimulus.
• Secondary affectedness revealed fish status, tendency toward or away from stimulus.
• Predators produced stronger effects than food as initial stimulus.

Zebrafish behavior was monitored based on continuous movement tracking of individuals in response to two conflicting stimuli, food and predators. The shape parameters describing positional distribution along the x-axis (mean, standard deviation (SD) and skewness) were differentiated according to source and time order (i.e., food first or predator first) of stimuli. Behavioral states were expressed by primary (mean and SD of x-coordinates) and secondary (skewness of x-coordinates) affectedness, and were addressed by specificity of individual response to stimuli. Even after adjusting spatial location and movement range in primary affectedness, secondary affectedness still occurred owing to a residual effect of the stimulus according to asymmetry of the positional distribution (e.g., away from the predator). Predator (as initial or secondary stimulus) produced stronger affectedness than food given as initial stimulus. Even after removal of initial stimulus, it still influenced affectedness of test organisms in the subsequent phases, implying memory effect of initial stimulus. Quantification of stress based on expression of behavioral state changes is feasible and could provide insight for monitoring based on indicator organism behavior under stressful conditions.