Chronic Erosive Dermatopathy (CED) Associated with Ectoparasite Infestation in Nile Tilapia Post-Larvae (Oreochromis niloticus Linnaeus, 1758)

Chronic erosive dermatopathy (CED) associated with ectoparasites was investigated in Nile tilapia (Oreochromis niloticus). Between 2023 and 2024, craniofacial lesions occurred at a prevalence of <1% across culture stages. Histopathology showed epidermal goblet cell proliferation and disappearance of the muscular layer, with no active pathogens or inflammation. Clinical history indicated heavy ectoparasite infestations during the 0.1 g fry stage, supported by parasite remnants found in deep skin scrapes of CED lesions. A clinical trial assessed this link using 3000 post-larvae (0.01 g each), divided into a control group (untreated) and a treatment group (tank water disinfected with 75% chlorine powder to 15 ppm for 24 h before stocking). Sampling 30 fish weekly for three weeks revealed CED incidence rates of 30% (9/30), 40% (12/30), and 27% (8/30) in controls, whereas the treatment group developed no lesions. The odds of developing CED were 25.7-, 40.0-, and 21.8-fold higher in controls at weeks 1, 2, and 3, respectively. These findings suggest early-stage ectoparasite infestations contribute to CED development. Implementing strict sanitary measures from post-larval stages is essential to minimize prevalence.