Cichlidogyrosis in tropical aquaculture: pathological effects and infection dynamics in Nile tilapia Oreochromis niloticus, a case study in Campeche, Mexico

Abstract

ABSTRACT Cichlidogyrus spp. are dactylogyridean ectoparasites of wild cichlids and cultured Nile tilapia that occur in several regions worldwide. They can be abundant in intensive Nile tilapia culture and cause mild to severe gill pathogenic effects that frequently are overlooked. From January to June 2018, a follow-up study was conducted on an intensive farm where 360 Nile tilapia were sampled and analyzed throughout a six-month culture cycle. During the survey, a population of monogeneans was observed to increase steadily over the course of the production cycle. To corroborate the status of these parasites, 13 additional farms were visited from January to April 2020, where a total of 130 Nile tilapia were examined. This secondary sampling aimed to identify and corroborate the dominant monogenean species and the infection dynamics, including the associated histopathological damages. Nine species of the genus Cichlidogyrus (Cichlidogyrus sp. C. bifurcatus, C. dossoui, C. halli, C. haplochromii, C. longicornis, C. sclerosus, C. thurstonae and C. tilapiae) were recovered from the gills and identified. Overall, Cichlidogyrus sclerosus was the most prevalent and abundant parasite. Also, significant differences were found in the monthly prevalence and intensity of C. sclerosus, especially in the fourth month of culture when the population peaked (Chi-square, p < .001; p < .001, respectively). Correlations were observed between temperature, nitrite, and C. sclerosus intensity. Four left gill arches of 130 Nile tilapia collected in the farms were removed and fixed at 10% formalin for histopathological examination. Histological alterations in gills tissues were graded by severity scores. Gills, at the site of monogenean attachments, showed mucus secretion, hyperplasia, hypertrophy, and lamellar fusion involving mucous cells, depending on the intensity of the damage.