Diet-mediated social networks in shoaling fish

Very little is known about interaction patterns within animal groups, such as flocks of birds, swarms of insects, or shoals of fish, or the mechanisms which mediate interactions between group members. Fish, such as three-spined sticklebacks (Gasterosteus aculeatus), are known to use a variety of visual and olfactory cues to inform shoal choice and to maintain shoal cohesion. However, whether these cues may also mediate interactions within a shoal is not known. This study aimed to investigate individual level interactions between shoaling sticklebacks under different diet treatments. Fish fed on either bloodworm- or Daphnia-based diets were used to generate replicated social networks (n = 65), in which the constituent fish differed in diet treatment. The results showed that the structure of stickleback networks is nonrandom and mediated by an association preference for fish from the same diet treatment, most likely through diet-derived chemical cues. The findings of this study provide insights into the causes of intragroup interactions in shoaling fish and highlight the importance of chemical cues in stickleback communication.