Environmental plastic pollution is a major ecological and societal concern today. Over the past decade, a broad range of laboratory and experimental studies have complemented field observations in the hope of achieving a better understanding of the fate and impact of micro- and/or nanoplastics (MP/NP) on diverse organisms (e.g., birds, fish, and mammals). However, plastic pollution remains challenging to monitor in the environment and to control under laboratory conditions, and plastic particles are often naturally or experimentally co-contaminated with diverse chemical pollutants. Therefore, our understanding of the effects of virgin MP/NP in freshwater and marine fish is still limited. Here, we performed a systematic review of the most up-to-date literature on the effects of virgin MP/NP on fish under laboratory conditions. A total of 782 biological endpoints investigated in 46 studies were extracted. Among these endpoints, 32% were significantly affected by exposure to virgin MP/NP. More effects were observed for smaller plastic particles (i.e., size ≤20 μm), affecting fish behavioral and neurological functions, intestinal permeability, metabolism, and intestinal microbiome diversity. In addition, we propose suggestions for new research directions to lead toward innovative, robust, and scientifically sound experiments in this field. This review of experimental studies reveals that the toxicity of virgin MP/NP on fish should be more systematically evaluated using rigorous laboratory-based methods and aims toward a better understanding of the underlying mechanisms of this toxicity to fish.