Abstract
Climate change directly affects the distribution and host switching of fish parasites. Temperature increases parasite metabolism further increasing its feeding and replication inside a host thus severely inducing damage. Higher temperatures often increase parasite growth, reproduction and infectivity yet can also escalate parasite mortality. This study highlighted the effects of stocking density and seasonality on monogenean and digenean trematode parasites in Oreochromis niloticus in cages in Uhanya Beach, Lake Victoria, Kenya. Parasites isolated from the sampled fish were the monogenean Dactylogyrus and the digenean; Tylodelphys, Clinostomum, and Neascus. Dactylogyrus sp. was predominantly abundant in the fish from all 10 cages. Mann-Whitney U-test revealed that the mean intensity of Dactylogyrus sp. infestation significantly increased with increased fish stocking density (p < 0.05; df =298). On the contrary, Clinostomum sp., Tylodelphys sp., and Neascus sp. exhibited significantly reduced infestation with increased stocking densities (p < 0.0001). Temperature significantly differed between the seasons (df = 28; p < 0.0001). Kruskall-Wallis test indicated significant variation in the prevalence of attack between the parasite species both in the wet season (H = 17.793; df = 3; p < 0.0001) and dry season (H = 30.226; df 3; p < 0.0001). There was a general positive correlation between water temperatures and mean parasite intensity, however, this relationship was weak in all the parasite species (r2 < 0.5). This study found no significant variation in temperatures and total dissolved solids (TDS) between the dry and wet seasons in cages where stocking density was 2000 (p > 0.05). Findings show that fish exposure to stressors such as water temperature, low DO and high stocking densities have a significant increase in the pathogenicity of the invading pathogens.
Keywords: Climate Change, Parasite-Host Interactions, Distribution, Host Switching, Tilapia Aquaculture.