The impact of water pH on association preferences in fish

Acidification of lakes and rivers, as a consequence of anthropogenic interference, can cause fundamental changes to biological and ecological processes. One of the main consequences of a reduction in water pH for aquatic organisms is the disruption of their chemosensory abilities, as the detection of chemical cues underpins a wide range of decision-making processes; for example, a reduction to low pH has been shown to interfere with predator avoidance and the detection of foraging cues. Moreover, aquatic organisms are known to make widespread use of chemical information to inform their social behaviour, although we have a comparably poor understanding of how this is impacted by water acidification, especially their shoaling behaviour. Using a standard behavioural assay, we therefore investigated the impact of low water pH on the social interactions mediated by diet-derived chemical cues in three-spined sticklebacks (Gasterosteus aculeatus), by quantifying social behaviour in water that varied either experimentally or naturally in pH. In both cases we predicted that association patterns would be disrupted by low pH conditions, as reduced pH has shown to interfere with the perception of chemical cues in other non-social contexts. Consistent with this prediction, our results demonstrate that an acute, short-term reduction in water pH caused a breakdown in the diet-mediated social interaction patterns seen in more alkaline water, although, interestingly, the pattern of associations for fish tested in naturally acidic water was both more complex and in a direction that was precisely contrary to our predictions. Overall the findings provide insights into the potential effects of an acute reduction in water pH on fish communication and social interaction patterns, which may have implication for various individual, group, population and community-level processes

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 communicatio

Animal welfare: a social networks perspective

Social network theory provides a useful tool to study complex social relationships in animals. The possibility to look beyond dyadic interactions by considering whole networks of social relationships allows researchers the opportunity to study social groups in more natural ways. As such, network-based analyses provide an informative way to investigate the factors influencing the social environment of group-living animals, and so has direct application to animal welfare. For example, animal groups in captivity are frequently disrupted by separations, reintroductions and/or mixing with unfamiliar individuals and this can lead to social stress and associated aggression. Social network analysis of animal groups can help identify the underlying causes of these socially-derived animal welfare concerns. In this review we discuss how this approach can be applied, and how it could be used to identify potential interventions and solutions in the area of animal welfare