Microplastics in marine fish: a mini-review on presence, classification, and impacts

Plastic production has experienced exponential growth in recent years due to its diverse industrial applications, low cost, and high availability, also causing issues, since plastic waste in aquatic ecosystems transforms into microplastics (MPs) through mechanical and weathering processes. Microplastics are distributed ubiquitously in water bodies, where they can be ingested by a wide aquatic organism range, including fish, which have been used as bioindicators to assess microplastic presence and toxicity. Research has revealed microplastic presence in various fish species worldwide; the most common characteristics are fibers and fragments of blue, black, and transparent colors, and polyethylene, terephthalate, polypropylene and cellophane chemical composition. Experimental studies under laboratory conditions have demonstrated microplastics impact on fish, showing physical, immunological, and hematological damage, and oxidative stress ultimately leading to organisms' death. However, laboratory results do not necessarily predict impacts on wild fish due to different conditions to which the organisms are exposed. Therefore, further research needs to simulate real scenarios faced by wild fish in the marine environment, providing greater certainty about microplastic impacts and negative effects.