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Although the ingestion of microplastics by fish has been investigated extensively over the last 50 years, the quality of these ingestion studies is questionable due to the lack of standard methods for sampling, extraction, and identification of microplastics. This review aims to provide reliable results of microplastic occurrence in fish sourced from 104 published articles through a rigorous assessment of the data quality. A scoring system was performed to assess ten quality assurance/quality control criteria including sampling methods, sample size, sample processing and storage, laboratory preparation, clean air conditions, negative controls, positive controls, target component, sample treatment and polymer identification. We found that 59 out of 104 articles had scores ≤10, and only two studies are identified with scores higher than 15, demonstrating the urgent need to improve the quality and reliability of fish digestion studies. Particularly, five criteria, namely, the positive controls, sampling method, clean air conditions, sample size, and polymer identification with an average score of less than 1 need attention and improvement in future studies. This review also revealed that the 104 studies considered here originated mainly from five countries, i.e., China (23%), Iran (8%), Thailand (5%), Turkey (4%), and Indonesia (4%). Among 104 studies, the major polymer type found was polyethylene, with a size range of 0–1 mm. The most frequently reported colour and shape of microplastics found in the fish were blue and fibre, respectively. [ABSTRACT FROM AUTHOR]