The effects of isolation and experience on preference for large shoals in juvenile fish

Abstract

Shoaling behaviour confers fitness benefits that depend on individual fish making specific choices of shoalmates. Some of these choices have been shown to be influenced by experience, raising questions as to whether all shoaling choices depend on experience. Here we show that juveniles of three fish species, zebrafish (Danio rerio), pearl danios (Danio albolineatus) and guppies (Poecilia reticulata), were all capable of discriminating between shoals of differing size, choosing to swim near the larger shoal, without any prior experience with other fish. Both zebrafish and the closely related pearl danio, reared in isolation until 40 days of age, spent significantly more time near a shoal of four conspecifics over a solitary fish. Guppies raised in isolation until 50 days of age spent significantly more time near a shoal of four conspecifics over a shoal of two conspecifics. These results demonstrate an innate ability in juveniles of these species to choose large shoals over small shoals. However, when guppies were raised in groups of three they did not demonstrate a significant preference for larger shoals, suggesting that experience can still play a role in size preference in shoaling behaviour.