Microscopic Evidence of Suspected Microplastic Ingestion in Guppies (Poecilia reticulata) from a Polluted Urban Drain on a University Campus: A Preliminary Study

Abstract

Microplastic contamination is an increasing concern in freshwater ecosystems, particularly in urban drainage systems receiving domestic inputs and surface runoff. This study investigated the occurrence and morphological characteristics of suspected microplastics in the gut contents of guppies (Poecilia reticulata) collected in December 2025 from a polluted freshwater drain near Universiti Putra Malaysia, Selangor, Malaysia. Ten individual guppies were examined using light microscopy following direct gut dissection and homogenization, without chemical digestion or density separation. Microscopic examination revealed morphologically diverse suspected microplastic particles, with fibre-type particles representing the most frequently observed form. In addition to isolated fibres, film-like particles, irregular fragments, and aggregated fibrous material associated with organic detritus and gut residues were observed. The particles varied considerably in size, ranging from approximately 162 to 690 µm, demonstrating the ingestion of both relatively small and comparatively large particles. The occurrence of suspected microplastics intermixed with organic detritus suggests that these particles may be ingested incidentally together with natural food materials. Considerable variation in particle size and morphology further indicates heterogeneity in the suspected microplastic particles ingested by guppies inhabiting the polluted freshwater drain. As polymer composition was not chemically confirmed, the observed particles are conservatively classified as suspected microplastics based on their morphological characteristics, including the absence of visible cellular structures and their relatively uniform, synthetic-like appearance. Overall, the findings demonstrate the occurrence and morphological diversity of suspected microplastics in guppy gut contents and support the potential use of small freshwater fish as sentinels of microplastic contamination in polluted urban drainage systems.

Keywords: Microplastics; Freshwater Fish; Poecilia reticulata; Gut Content Analysis; Urban Drainage Pollution

Citation

Yap CK, Mohd Hadir MI, Ramlee MA, Latif MM, Syukran Baharuddin MA, Hashim EI, et al. Microscopic Evidence of Suspected Microplastic Ingestion in Guppies (Poecilia reticulata) from a Polluted Urban Drain on a University Campus: A Preliminary Study. WebLog J Environ Sci. wjets.2026.i2102. https://doi.org/10.5281/zenodo.23194152