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Plastics as disruptors of feeding, digestive physiology, metabolism, and growth in fish and other aquatic ectothermic vertebrates
Summary
This review pulls together existing research showing that tiny plastic particles in water are messing with fish and other aquatic animals' ability to eat, digest food, and grow properly, partly by tricking their bodies into feeling "full" and throwing off hormones that control appetite and metabolism. This matters for us because these effects could impact fish farming and wild fish populations that people rely on for food, and warming waters from climate change may make the problem worse by increasing how much plastic gets into these animals' systems.
Plastics, particularly microplastics (MPs) and nanoplastics (NPs), are widespread contaminants in aquatic ecosystems that affect key physiological processes related to feeding, digestion, metabolism, and growth in aquatic ectotherms, particularly fish. Increasing evidence indicates that plastic exposure disrupts energy balance by reducing food intake through false satiety, gastrointestinal obstruction, and behavioral alterations, while also impairing digestive efficiency, nutrient absorption, and metabolic regulation. MPs and NPs can interfere with endocrine signaling pathways involved in appetite regulation. They may also disrupt the thyroid axis, a key regulator of metabolism and energy expenditure, and the growth hormone/insulin-like growth factor axis, which controls somatic growth and nutrient partitioning. These endocrine disturbances are often accompanied by oxidative stress, impaired hepatic function and gastrointestinal integrity, ultimately affecting growth performance, energy allocation, and overall fitness. While these effects are best documented in fish, amphibians show similar but less well-characterized responses, whereas evidence in reptiles remains limited and largely observational. The impacts of plastics are further modulated by environmental conditions associated with climate change. Factors such as temperature and salinity can influence the uptake, bioavailability, and toxicity of MPs and NPs, often exacerbating their effects on feeding behavior, metabolic performance, and endocrine function. In addition, climate-driven processes -including warming, extreme weather events, and changes in ocean circulation - can alter the breakdown, transport, and distribution of plastics, potentially increasing exposure risks. However, high heterogeneity in experimental protocols, such as differences in plastic characteristics, exposure concentrations and durations, species, and life stages, limits direct comparison across studies. This review synthesizes current knowledge on the effects of plastic exposure on feeding, digestion, metabolism, and growth in aquatic ectotherms, with a particular focus on fish, while integrating available evidence from amphibians and reptiles. It also highlights underlying mechanisms and the influence of environmental conditions, with implications for fish health, aquaculture productivity, and ecosystem functioning in increasingly polluted aquatic environments.