Infestation and Transmission Patterns of Monogeneans in Cultured and Wild Nile Tilapia (Oreochromis niloticus, Linnaeus, 1785) in Lake Victoria

Abstract

Parasitic cross contamination occurs between cultured and wild fish. This study investigated infestation levels and transmission patterns of monogenean parasites across hatchery, caged and wild Nile Tilapia, Oreochromis niloticus. Two hundred ninety-one fish samples randomly collected over a period of seven months were examined for monogeneans using standard parasitological methods. Level of infestation was determined using proportion of infested fish and mean intensity. Meanwhile, the transmission pattern was assessed using genetic diversity and differentiation across the sampling units based on amplification and sequencing of the 28S rDNA region. The fish fry from the hatchery did not harbor monogenean during this study. The mean intensity of monogeneans on cage fish (4.44±0.13 parasites/fish) was significantly different from that recorded in wild hosts (2.00±0.03), suggesting continuous parasite accumulation on caged fish. However, both populations had similar monogenean proportions of infested hosts (77%) owing to the close proximity of the systems. Monogenean parasites on caged O. niloticus had a higher genetic diversity (hd = 1.000±0.100, π = 0.343±0.154) than the wild hosts (hd = 0.833±0.167, π = 0.321±0.104), pointing to a high evolutionary potential of the parasites. The genetic differentiation (Fst = 0.24, p = 0.369) was non-significant, suggesting substantial gene flow and cross transmission of monogeneans between caged and wild hosts. These findings, therefore, show a need to develop effective biosecurity measures to safeguard both farmed and wild fish from parasites for aquaculture sustainability.