Microplastics are now found in every aquatic environment on Earth. Their effects on fish, invertebrates, and marine mammals include reduced feeding, hormonal disruption, and physical injury with significant welfare implications.
Microplastic welfare impacts on aquatic animals are insidious because they are invisible and diffuse. Fish that are not visibly ill may have reduced reproductive success, impaired immune function, and hormonal disruption from microplastic ingestion. These sub-lethal effects reduce quality of life in ways that are difficult to observe and quantify but are real welfare harms. Filter feeders that cannot avoid microplastic ingestion are particularly exposed. The scale of contamination -- affecting every aquatic environment on Earth -- makes this one of the most widely distributed welfare threats to aquatic animals in history.