Quantifying microplastics in fishes: The first case study contrasting the perspective of untrained and experienced researchers

Microplastic studies hold a low explored potential for citizen science and environmental education, but methodological issues challenge data produced by non-specialists. We compared microplastic abundance and diversity in the red tilapia Oreochromis niloticus recovered by untrained students with those recovered by researchers that have experience of three years studying the incorporation of this pollutant by aquatic organisms. Seven students dissected 80 specimens and performed digestion of digestive tract in hydrogen peroxide. The solution was filtered and inspected under a stereomicroscope by the students and by two expert researchers. A control treatment consisted of 80 samples handled only by experts. The students overestimated the abundance of fibers and fragments. Striking differences in abundance and richness of microplastics were verified between the fish dissected by students and by expert researchers. Therefore, citizen science projects involving the uptake of microplastics by fish should provide training until a satisfactory level of expertise is reached. •Microplastic (MP) in fishes were analyzed by undergraduate students and specialists.•Students overestimated the abundance of fibers and fragments by at least two times.•Fish dissected by students presented the highest MP abundance and richness.