Background: Microplastics (MPs) have emerged as a growing research focus in aquatic environments, particularly within freshwater aquaculture systems in recent years. However, the presence and characteristics of MPs in Iran’s freshwater aquaculture systems remain unexplored.
Objectives: To address this gap, this study aimed to quantify and characterize MPs in freshwater aquaculture systems across two regions: Mazandaran and Golestan provinces in Iran.
Methods: Thirty samples of Oncorhynchus mykiss from each area were collected from a pool in the fall of 2024. MPs were extracted from the gastrointestinal tract, gills, and liver and analyzed for abundance, shape, size, and polymer type/compound. Their polymer compositions were determined using a Fourier transform infrared spectroscopy (FTIR).
Results: The digestive tract had the highest abundance of MPs (26±11 particles/g) and the liver had the lowest abundance (2±0.2 particles/g). The average MPs observed in all tissues studied was 83.11±92.5 particles. The highest abundance was fiber MPs (92.96%) and the lowest abundance was fragments (7.04%). The 300-600 µm group had the highest abundance (31.37%), while the 3000-5000 µm group had the lowest abundance (5.88%). Black color had the highest abundance (54.9%) and pheasant color had the lowest abundance (1.96%). The polymer composition of MPs included polyethylene (PE; 57.14%), polyethylene terephthalate (PET; 23.81%), polypropylene (PP; 9.52%), and polyester (PS; 9.52%).
Conclusion: All examined fish contained plastic particles, mainly in the gastrointestinal tract. Common MPs were synthetic fibers from PE and PET. While plastic can bioconcentrate in tissues, it does not bioaccumulate significantly, indicating low biomagnification potential in rainbow trout. Recirculating aquaculture systems (RAS) components contribute minimally to contamination.