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Fish show leadership qualities when threatened

Posted on 31/05/17 in News

By Heather Chinn 

The times make the man the saying goes - and also the fish, according to a new scientific study.

Individual fish in shoals threatened by predators appear to take on the role of leader, guiding the shoal’s actions, researchers from the University of Bristol have found.

Shoals less at risk from predators were correspondingly less likely to have individuals acting as leaders.

Scientists from the university’s School of Biological Studies believe the study suggests the guppies they observed are altering their behaviour in response to the levels of threat, but added further research is still needed.

The researchers found the majority of decisions made by leader fish are followed, making a shoal a tighter knit group, and so more effective at evading predators.

Dr Christos Ioannou said: “There are many benefits of group living, and making decisions together can dramatically increase the survival of many species - this is why many birds flock and fish shoal.

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“Groups can be guided by leaders, where a single individual makes most of the decisions, or egalitarian, where everyone contributes.”

During the study, reported in Science Advances and funded by the UK’s Natural Environment Research Council, the researchers examined the behaviour of over 300 guppies from rivers with varying levels of risk from predators.

The fish were placed in a maze, and decision making and the unity of each shoal were measured using computer tracking software.

Fish from rivers with high levels of predators tended to divide into leaders and followers. The majority of the decisions made by the leaders were followed by the remaining members of the shoal, and shoals with leaders were tighter knit than more egalitarian shoals.

Dr Ioannou added: “The study shows that decision making in social groups within a species can vary depending on predation, even within a small geographical range.

“Changes in decision making may be a direct response to predation risk, but we need further experiments to test this.

“The research is important as it shows that social behaviour can adapt depending on ecological factors.

“This could have a wider impact when considering how changes in species communities, for example, due to climate change or invasive species, affect social prey.”

Picture: Crenicichla frenata are the major aquatic predator of adult guppies. Credit: Andrew Szopa-Comley