Robison

A New Species Of Myxobolus (Cnidaria: Myxosporea: Myxobolidae) From The Skin Of Nile Tilapia, Oreochromis Niloticus (Cichliformes: Cichlidae) From Lake Victoria, Uganda

1Logan R. S. Robison, 2Justin M. Stilwell, 2Ethan T. Woodyard, 2,3Stephen R. Reichley, 4Andrew Omara Rwot, 4David Kahwa, 4Celsus Sente, 1Thomas G. Rosser

1Department of Comparative Biomedical Sciences, Mississippi State University, 240 Wise Center Drive, Starkville, MS 39762; 2Department of Pathobiology and Population Medicine, Mississippi State University, 240 Wise Center Drive, Starkville, MS 39762, 3Global Center for Aquatic Health and Food Security, Mississippi State University, 240 Wise Center Drive, Starkville, MS 39762, 4College of Veterinary Medicine, Animal Resources and Biosecurity (COVAB), Makerere University, P. O. Box 7062, Kampala, Uganda

ABSTRACT

Nile Tilapia (Oreochromis niloticus) is a host for many species of myxozoan parasites within the genus Myxobolus. There is potential for issues with these parasites with the presence of Oreochromis niloticus in the aquaculture industry around the world. Being a fast-growing fish with high reproductive potential makes this species easy to grow in an aquaculture setting. These previous qualities also give Oreochromis niloticus its highly invasive tendencies and ability to cause severe damage to native fish populations if they escape confinement in non-native areas. In Uganda, fisheries and aquaculture has become a major economic resource capable of providing a sustainable supply of protein. Nile Tilapia are primarily reared in fry ponds and open net pens in Lake Victoria. At one farm during June 2022, fry reared in ponds were sampled for routine diagnostics. At necropsy, numerous pinpoint, raised white areas were observed on the epidermis. Further examination demonstrated these to be plasmodia containing too numerous to count myxospores of a Myxobolus species. Myxospores were examined microscopically and had a total length of 16.2 – 18.9µm (17.5 + 0.7µm) with a width of 10.9 – 12.9µm (12 + 0.4µm) spore thickness was 8.09 – 8.91µm (8.5 + 0.3µm). pyriform shaped polar capsules were spilt into two categories the large polar capsule which had a length of 6.33 – 7.89µm (7.07 + 0.4µm) and a width of 3.28 – 4.56µm (3.8 + 0.3µm) and small polar capsule with a length of 6.07 – 7.48µm (6.7 + 0.4µm) and width of 3.29 – 4.43µm (3.8 + 0.3µm). The main visible effect on the fish were the pinpoint, raised areas on the epidermis. Fish were submitted for routine histopathological assessments to assess the extent of the lesions. Sequencing of the 18S and 28S rDNA for the Myxospores was done and they appear to be morphologically and molecularly distinct from previously described Myxobolus spp. from Tilapia. Therefore based on the morphological, histopathological, and molecular data generated and comparisons to accounts in the literature there is potential for this to be a novel Myxobolus species.

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