Depth-structured patterns of monogenean parasites in Eastern Pacific fish: a historical dataset (1967-1980)

Monogenean parasites are among the most common ectoparasites of marine fishes and can influence host health, fitness, and population dynamics. Despite their ecological importance, historical data on monogenean prevalence and diversity in marine fish are scarce. Here, we report data from a historical survey of 1,518 fish, representing 242 species across 87 families, collected from the Central California coast to the Gulf of California between 1967 and 1980. Monogeneans were identified from gills, skin, and body openings, and prevalence and mean abundance were analyzed across five depth zones: sub-littoral, epipelagic, mesopelagic, bathypelagic, and bathyal. Infections were concentrated in sub-littoral and epipelagic fishes, with prevalence and diversity declining in deeper habitats, likely reflecting host density, environmental conditions, and parasite life history. A total of 42 monogenean species from 14 families were recorded, including several undescribed taxa. This historical dataset provides a rare baseline for Pacific marine fishes and offers a valuable reference for assessing long-term changes in parasite populations and host-parasite dynamics under environmental change.