Assortative preferences for stripes in danios

Decisions about joining social groups are often contingent on one’s own phenotypic characteristics and those of existing group members. Zebrafish and their allies (genus Danio) vary substantially in the expression of conspicuous lateral stripes. We presented wild-type zebrafish (D. rerio), two artificially selected D. rerio strains with reduced stripe expression, as well as the stripeless D. albolineatus and the striped D. nigrofasciatus, with simultaneous choices between synthetic, computer-animated shoals of stripeless and striped Danio. Each species and strain of Danio preferred the phenotype that most resembled its own, with a strong preference for striped stimuli by fish with dark-stripe phenotypes, and a strong preference for no stripes by fish lacking stripes. Stripes are therefore a key shoaling cue in Danio. Individuals appear to acquire a general preference for stripes, or no stripes, as a consequence of experience with a specific stripe phenotype.