Standard Operating Procedure for the Analysis of Microplastics in Larval Fish Diets

Microplastics (MPs) pollution has increasingly exposed the pelagic biota to physical harm. The small size of micro-particles makes them more suitable for passive ingestion by a wide variety of organisms with serious effects on growth rates, respiration and vital functions, bioaccumulation of pollutants, and, ultimately, species survival. Nevertheless, our knowledge of plastic intake in nursery habitats is still very limited. When encounters with MPs occur at the larval stage, it is suggested that fish can develop altered feeding behaviors with cascading effects on the entire food web. This study provides a step-by-step protocol to identify and enumerate polymer particles found in fish diets. The procedure is intended for the analysis of larval and juvenile fish populations with a developed digestive tract. It includes guiding questions for research design, a list of supplies and reagents to extract and mount the fish diets on microscope slides for semi-permanent conservation, the protocol for microscopic and statistical analysis, and the interpretation of the results. We suggest that the gut content could be used to assess (i) the bioavailability of polymers in water systems, (ii) the incidence of an encounter between larval fish and MPs, and (iii) the possible alternations in fish’ feeding behaviors as soon as they leave their parental stage.