Marine vertebrates that feed on plankton, such as small fish and filter feeders, are particularly vulnerable to plastic pollution. This is due to their feeding behaviour, which primarily involves the ingestion of detritus in the water column or filtration of large volumes of water. As a result, these organisms are at an increased risk of ingesting microplastics. However, the extent to which plastics affect wildlife remains unclear. In this study, 61 black striped salemas (Xenocys jessiae) sourced from six different bays on one Galápagos National Park (GNP) Island (San Cristóbal) were subjected to a thorough examination of the prevalence of plastic in their gastrointestinal tracts (GT) and compared it with a suite of health metrics (vital signs, hematology, and blood chemistry). Plastic pollution in the surrounding habitats was also assessed, and it was found in all sampled X. jessiae habitats. Pressurized liquid extraction with double-shot pyrolysis-mass spectrometry gas chromatography (Pyr-GC/MS) revealed plastic pollution in the GT of the fish. Polyethylene (PE) x̄ = 535±743 (range:0-2327) μg/g was the polymer with the highest mass concentration in GT, and polypropylene (PP) x̄ = 138±143 (range:0-751) μg/g was also abundant. Furthermore, these levels differed significantly according to the sampling site. The highest concentrations of plastics were found in fish collected from off-limits GNP and fishing areas. Consequently, the fishing and tourism industries are likely the primary contributors to this problem. This study is the first to use Pyr-GC/MS to quantify the plastic pollution in commercial fish in Galápagos. This technique detected and quantified plastic pollution in the GT of 56 X. jessiae (92%) of the sampled population. Our collected data on plastic pollution, vital signs, morphometry, and blood values served as a baseline for future comparisons.