In this study, patterns in the taxonomic richness and composition of the fish fauna inhabiting Cymodocea nodosa seagrass meadows were described across their entire distribution range in the Mediterranean Sea and adjacent Atlantic Ocean. Specifically, the study tested whether there are differences in the composition of fish assemblages between those ecoregions encompassed by the distribution range of C. nodosa, and whether these differences in composition are connected with differences in bioclimatic affinities of the fish faunas. A literature review resulted in a total of 19 studies, containing 22 fish assemblages at 18 locations. The ichthyofauna associated with C. nodosa seagrass meadows comprises 59 families and 188 species. The western Mediterranean (WM) Sea has the highest species richness (87 species). Fish assemblages from the Macaronesia-Canary Islands, the Sahelian Upwelling, South European Atlantic Shelf and the WM differ, in terms of assemblage composition, relative to other ecoregions. In contrast, the composition of the fish fauna from the central and eastern Mediterranean overlaps. There is a significant serial correlation in fish assemblage composition between adjacent ecoregions along the distribution range of C. nodosa. Dissimilarities in assemblage composition are connected with the geographical separation between locations, and the mean minimum annual seawater temperature is the environmental factor that explains most variation in fish assemblage composition.