Population dynamics of Cichlidogyrus spp. and Scutogyrus sp. (Monogenea) infecting farmed tilapia in Veracruz, México

• Cichlidogyrus spp. and Scutogyrus spp. are common monogenean gill parasites of farmed tilapia.
• C. sclerosus was the most abundant parasite in this survey; and worm burdens were negatively associated to water temperature.
• Infection with C. sclerosus may induce anemia in farmed tilapia.

Four genetic groups of cultured tilapia (Oreochromis spp.) were kept under aquacultural conditions (i.e., not controlled experimental conditions) and monitored for one year to investigate factors associated with variation in prevalence and mean abundance of the monogenean parasites Cichlidogyrus sclerosus, Cichlidogyrus dossoui and Scutogyrus sp. infecting the gills; overall, C. sclerosus presented the highest mean abundance. A significant, negative association was found between water temperature and parasite burdens. No significant correlations were recorded between parasite numbers and either host size or coefficient of body condition—no hematocrit values were recorded for these hosts. However, a group of juvenile fish from the same farm studied separately which harbored lower parasite burdens than those documented in this survey, showed a significant negative correlation between parasite abundance and hematocrit values, suggesting that infection may be detrimental to hosts.