Prevalence and intensity of ectoparasites in Nile tilapia hatcheries in Homa Bay County, Kenya

Abstract

Nile tilapia is the most preferred fish species for rearing and human consumption in Africa. Despite being a prolific breeder, demand for tilapia seeds remains high, and hatcheries have been established to meet this demand. However, hatcheries face significant challenges with high costs associated with feed, electricity, fish diseases and parasitism. A study was conducted in two hatcheries in Homa Bay County, Kenya in March and April 2023, in a bid to establish the prevalence and intensity of ectoparasites on various age groups of Nile tilapia (Oreochromis niloticus) in these facilities. One hundred and forty samples were collected from the two hatcheries and examined in-situ. These included 20 scoops each for eggs, fry and larvae and, 40 pieces each for brood stock and fingerlings. The eggs, larvae and fry were examined wholly under the microscope, while for fingerlings and brooders, skin scrapings, fin and gill clips were examined. Overall ectoparasite prevalence was 66% (92/140) and was highest in brooders (80%; 32/40) and lowest in larvae (10%; 2/20). Five genera were recovered, with the monogenean, Gyrodactylus being found in all age groups at a prevalence of 35% (49/140). Others included the monogenean, Dactylogyrus (12%; 17/140), ectopropozoans, Trichodina (11%; 16/140) and Epistylis (4%; (6/140) and the fish louse, Argulus spp. (0.7%; 1/140). The prevalence of Gyrodactylus spp. and Dactylogyrus spp. was statistically significant (X2=10, sig=0.039) and (X2=20, sig<0.001) in the hatcheries, respectively. The ciliate, Epistylis spp. had the highest mean intensity of 30.8 relative to other ectoparasites and there was a significant difference between the two farms (X2=4.4, sig=0.037). These findings indicate that ectoparasites are common in all age groups in hatcheries, and were most prevalent in brooders. Hatchery operators should implement strict biosecurity measures in order to avoid the spread of ectoparasites within the hatcheries and grower ponds.