Plastic Debris And Amazonian Fishes: A First Look

Plastic has become a major focus of ocean conservation efforts, and with good reason: plastic bags, bottles, fishing gear and other products degrade into micro- and meso-plastic particles after entering the water bodies. This pollution may then be ingested by fish which can cause internal injuries and blockage of the gastrointestinal tract, eventually resulting in starvation and death. In this study, a group of scientists from Brazil, the U.S. and Italy have presented the first evidence of plastic ingestion by freshwater fishes in the Amazon.

The research included inspecting stomach contents of 172 fish, representing 16 species of the family Serrasalmidae, for plastics, and the results were concerning. About one quarter of the tested fish and 81% of the studied species had consumed plastic pieces, ranging from 1-to-15 mm in length.

Despite feeding differences between the species, the frequency of occurrence of plastic and the weight of ingested plastic were not significantly different. However, the length of meso-plastics (defined as 5.1–25 mm pieces) differed significantly among the three trophic guilds (herbivorous, omnivorous and carnivorous), with the herbivores ingesting the longest pieces. The highest overall intake of plastic particles was recorded in omnivores at 18.6% , respectively.

The variation in ingested particle sizes is likely associated with behavioral differences, such as omnivores feeding heavily on larger aquatic plants that probably intercept and retain tiny plastic particles drifting in currents. Meanwhile, herbivorous serrasalmids (a family of fishes including piranhas and pacus) feed mostly on seeds, fruits, leaves and fragments from terrestrial plants, potentially ingesting larger plastic particles that are mistaken for food resources. Finally, piranhas may ingest plastic when they consume prey fishes who had ingested and retained plastic particles themselves, a form of plastic bio-accumulation.

Although it remains unclear why and how these fishes ingest plastic particles, we do now know that plastic pollution has become prevalent in the Amazon basin. This will add to the worries of animal advocates as the well-being of wild river fishes is evidently compromised by ingestion of plastic. For animal advocates working on issues related to plastic in our oceans and other waters, sharing this information with the public will be vitally important.