Decoy effect in shoaling decision making in zebrafish(Danio rerio)

ABSTRACT Several organisms, from slime molds to humans, are known to violate normative principles of economic rationality in decision making. In animals, the neural circuitry underlying behaviors that violate or conform to normative rationality is relatively poorly understood. We investigated whether zebrafish, a model organism with a strong suite of functional neuroimaging and genetic manipulation tools, showed a decoy effect with respect to the principle of the Independence of Irrelevant Alternatives (IIA). We examined IIA in social decision-making by measuring revealed preferences from spatial trajectories of freely swimming individual zebrafish in an arena where they could view and perform shoaling behavior near conspecific zebrafish in adjacent display tanks. IIA was tested in terms of the invariance of shoaling choices between binary and ternary sets of various display fish group sizes. We provide the first report of evidence for the decoy effect in male zebrafish, but not in females. This opens up a range of possibilities to study the neural basis of context-dependent decision making.