Color assortative shoaling in zebrafish, Danio rerio (Cypriniformes: Cyprinidae)

Abstract

Zebrafish, Danio rerio, form shoals consisting of loosely aggregated individuals swimming in different directions. Shoal-mate composition in fish can be influenced by body size, shape, coloration, and pattern. The effect of transgenic body coloration on shoal-mate composition in wildtype D. rerio was examined. A test arena was divided into three equal sections with a wildtype zebrafish in the center compartment. For control trials, a wildtype shoal of seven individuals was placed in both side compartments. For experimental trials, one of the wildtype shoals was replaced with seven green transgenic fish. The number of visits made to each side and the time spent on each side were recorded. Control fish showed no significant difference (NSD) in the average number of visits to the left versus right side and NSD in the average time spent with either shoal. Experimental fish exhibited NSD between the average number of visits to the transgenic versus the wildtype shoal, but they spent significantly more time shoaling with the wildtype. Wildtype test fish consistently visited each side, which would enable assessment of shoal composition, but spent more time shoaling with phenotypically similar individuals, as predicted by the oddity effect. Previous studies show no significant preference by wildtype D. rerio for wildtype versus red transgenic conspecifics and indicate a more prominent role of striping pattern. This generates further questions about the influence of body coloration on shoal-mate preference. Future research could examine the effect of other transgenic colors on shoal-mate preference.