Fish that display dominant traits are more at risk of consuming microplastic pollution than others in their social group, according to new research.

The study, led by the University of Glasgow and published in Proceedings of the Royal Society B, details the different levels of risk microplastic pollution poses to aquatic life, with some fish in hierarchical social groups affected more than others.

Researchers found that dominant fish in a group were more at risk of swallowing microplastics than their subordinates.

However, the data also showed that groups with clearer social hierarchies – including strong, dominant fish – were seemingly better at telling the difference between food and pollution, resulting in reduced microplastic ingestion overall.

In addition, the study found that microplastic ingestion risk was altered, in different ways for different fish, by flowing or still waters. For most fish, flowing water helped to reduce microplastic ingestion at both the individual and group levels. However, for dominant fish, flowing water had the opposite impact, causing an increase in the proportion of microplastic particles ingested.

The authors say their findings demonstrate, for the first time, that the kinds of dominant social traits usually associated with a competitive advantage may, in polluted habitats, make the strongest fish most vulnerable to microplastic pollution.

Professor Shaun Killen, Professor of Ecophysiology at the University of Glasgow and senior author of the study, said: “Plastic pollution is a growing ecological threat, yet the behavioural and social factors influencing susceptibility to microplastic ingestion have until now remained poorly understood. Our findings show that microplastic exposure is shaped not only by the environment, but also by social structure.”

To carry out the study, the research team focused on European minnows – a widespread species found in both flowing and still waters – which live in hierarchical groups ranging from a few individuals to several hundred fish. The researchers examined how social hierarchy and water flow influenced microplastic ingestion in groups by monitoring fish across multiple feeding bouts.

Dr Weiwenhui Liang, lead author of the study, said: “One important implication of this work is that water flow should not be treated as a minor background condition in microplastic research. Most experimental studies on microplastic effects have been conducted in still water, but many aquatic animals experience pollution in moving water.

“Our findings show that water movement can really change the picture. Because flow can interact with social behaviour and feeding, some individuals face risks that would otherwise be missed. Accounting for this could help us better understand which animals are most vulnerable to pollution in natural habitats.

“Dominance can be a double-edged sword. The traits that help some fish win access to food may also make them more likely to consume pollution when plastic particles resemble their regular food. This means that microplastic risk is not shared equally within animal social groups. It depends on who the fish are, how they behave, and the social environment around them.”

The study, ‘Intraspecific behavioural and environmental contexts influence collective risk of microplastic ingestion in a social fish,’ is published in Proceedings of the Royal Society B.

The work was supported by a China Scholarship Council grant and a UKRI Natural Environment Research Council.