Microplastic Analysis in Catfish Mystus gulio (Hamilton 1822) and Tilapia Oreochromis niloticus (Linnaeus 1758) from Tirunelveli District, Tamil Nadu, India

The microplastics (MPs) are less than 5 mm in length. The freshwater organisms, including fish, can consume microplastics. Here, we investigate the presence of microplastics in Mystus gulio and Oreochromis niloticus fish species. The fishes were collected from Suthamalli, Thamirabarani River, Tirunelveli. We identified the collected fish at the species level, and fish gastrointestinal tracts were dissected and ground with mortar and pestle. Samples were filtered, and dried in sunlight. The presence of microplastic particles was observed by the Olympus (CH20i) microscope. We analyzed the morphological variation (fiber, fragment and bead) and different colored (white, red, blue, brown, black and green) microplastics in the gastrointestinal tract of both species. The both fish Mystus gulio and Oreochromis niloticus Hepatosomatic Index (HSI), Gastro-Somatic Index (GSI), Splenosomatic Index (SSI) and Hyperosmotic Index (NSI) were calculated. In this study, MPs present in the gut of Mystus gulio, 33.3% of fiber, 61.90% of fragment, and 4.76% of beads were found. In Oreochromis niloticus, 36.36% of fiber and 63.63% of fragment were found. The isolated fish gut MPs were characterized by ATR-FTIR. The analysis confirmed the presence of polymers like, polyethylene terephthalate (PET), polypropylene (PP), polyamide (Nylon), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene (PE). Morphometric analysis further revealed that the highest degree of correlation was observed between the total length and the standard length for both fish species. This research provides proof that both fish species are contaminated by the MPs, the river ecosystem is contaminated by plastics.