Genetic parameters for black spot disease (diplopstomiasis) caused by Uvulifer sp. infection in Nile tilapia (Oreochromis niloticus L.)

Black spot disease (diplopstomiasis), an external melanized host inflammatory response caused by a number of digenetic trematode parasites, results in slow growth, deformities and increased mortality among many freshwater fish species globally. We investigated the severity of infection, and genetic parameters for black spot disease among 150 families of Nile tilapia (Oreochromis niloticus) of the Abbassa strain in ponds in Egypt. The causative agent for the black spot disease was identified molecularly as a Uvulifer species using 28S gene. Although 27% of the families remained completely unaffected, the others exhibited signs of black spot infestations randomly distributed in the skin and fins at different levels of severity. Histological examination revealed multiple parasitic cysts surrounded by fibrous capsules with melanin deposits embedded in the muscles. Females were significantly more susceptible than males (P