Comparative Study of Parasite Infestation of Pond and Cage Cultured Nile Tilapia (Oreochromis niloticus) in the Lake Victoria Crescent, Uganda

In recent years, intensification of aquaculture production in the Lake Victoria Crescent, Uganda has resulted in increased parasitic disease occurrences. However, despite the efforts made, the parasite burden has continued to cause fish mortality. Notably, the different production systems provide different habitats and environmental conditions for the parasites and understanding of the parasite infestation dynamics in these culture systems may provide better sanitary and farm management strategies for the parasite burden. Therefore, the study compared the parasite prevalence and mean intensity of pond and cage cultured Nile tilapia and also identified statistical associations between parasitic infestation and farm management practices. Across the Crescent, a high infestation rate of 65% (418/640) with Trichodina spp. being most prevalent and abundant, and a 16 parasite taxa; 6 protozoa, 2 monogenea, 2 digenea, 1 crustacea, 3 cestode, and 1 acanthocephala was obtained. Furthermore, nearly all parasites were recovered in 3 fish organs; gills harboring 50% (8/16), intestines with 31% (5/16) and skin with 25% (4/16) of the parasite genera. Fish from Pond grow-out and Hatchery farming system harboured ≥ 11 parasite genera while ≤ 5 parasite genera were found in Cage grow-out (lake) and Cage grow-out (reservoir) farms namely; Pond grow-out: 5 protozoa, 1 monogenea, 2 digenea, 1 crustacea, 2 cestode; Cage grow-out (lake): 2 protozoa, 1 monogenea, 2 digenea; Cage grow-out (reservoir): 2 protozoa, 1 monogenea, and Hatchery: 3 protozoa, 2 monogenea, 2 digenea, 1 crustacea, 2 cestode, and 1 acanthocephala. Definitely, Trichodina spp. and Dactylogyrus spp. were recorded in all culture systems but with Trichodina spp. having the highest prevalence and mean intensity in Cage grow-out (reservoir). After classification of infestation, the comparative assessment between Pond grow-out and Cage grow-out (lake) farming systems revealed that 66 % (12/18) of Pond grow-out farms had normal/ frequent infestation and with one farm having very severe/ severe infestation whereas, 33 % (3/9) of Cage grow-out (lake) had gradual/ rare infestation yet with no farm having very severe/ severe infestation. The Fisher's exact test revealed that in Pond grow-out, the relatively high infestation was significantly associated with all the farm management practices: fish seed source, stocking density, feeding and nutrition, disinfection, control of intermediate hosts, and control of wild fish entry, while in Cage grow-out (lake), the relatively low infestation was only significantly associated with stocking density, feeding and nutrition, and control of wild fish entry. Therefore, the findings from the study suggest that proper farm management practices will reduce on the parasite proliferation in the Crescent.