Location: Warmwater Aquaculture Research UnitTitle: Kudoa thunni from blackfin tuna (Thunnus atlanticus) harvested off the island of St. Kitts, West Indies Author
Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2013
Publication Date: 1/1/2014
Citation: Griffin, M.J., Quiniou, S., Soto, E. 2014. Kudoa thunni from blackfin tuna (Thunnus atlanticus) harvested off the island of St. Kitts, West Indies. Journal of Parasitology. 100(1):110-116. Interpretive Summary: Parasites in the genus Kudoa are of significant economic concern to aquaculture and wild-catch fisheries because of the potential negative impacts on product quality, whether from the unsightly presence of parasites within the musculature or from post-mortem degradation of the fillet. Here we describe a Kudoa species previously unreported from the musculature of blackfin tuna harvested off the Caribbean island of St. Kitts. Genetic analysis linked the case isolate to parasites of other economically important tuna species, suggesting this parasite is widespread and could have significant impacts on cultured and wild-catch fisheries in the western Atlantic.
Technical Abstract: Numerous histozoic myxosporidian cysts (~1 mm) were found in the musculature of blackfin tuna (Thunnus atlanticus) harvested by local fisherman off the Caribbean island of St. Kitts in 2011 and 2012. The ellipsoidal, polysporous cysts contained myxospores consistent with members of Kudoidae. Morphologically, this case isolate shared several characteristics with other Kudoa spp. from marine fishes. Myxospores measured 7.3 (6.8-8.2) µm in length, 6.1 (5.2-6.7) µm in breadth, containing 4 uniform drop-like polar capsules measuring 2.2 (2.0-2.5) µm in length and 1.8 (1.4-2.0) µm in breadth. The suture radius was 2.6 µm (2.5-2.8). Genetic sequencing of the 18S small-subunit (SSU) and 28S large-subunit (LSU) ribosomal DNA sequences did not result in any direct matches over nearly 1,700 bp and 800 bp, respectively. SSU sequences were homogenous, demonstrating a high degree of similarity (>99.0%) to two different species, K. crumena (99.6%; 1623/1629 bp) from yellowfin tuna (Thunnus albacares) and K. thunni (99.0%; 1746/1763 bp) from an albacore (Thunnus alalunga). However, multiple sequences were obtained for the LSU, demonstrating 0.1 to 3% variation between them. By comparison, the published LSU sequences for K. crumena and K. thunni share 99.4% sequence homology (797/802 bp). Further compounding this ambiguity is the fact the K. crumena sequences are not linked to any published morphological description. Morphologically, the case isolate was distinctly smaller than published morphological descriptions for either K. thunni or K. crumena, sharing the greatest similarity to K. amamiensis from reef fishes in Australia. However, genetic sequence data suggests the case isolate and K. amamiensis are not conspecific (LSU; 84.7%; 582/684 bp). The intraspecific diversity of the LSU rDNA gene for this isolate, some of which demonstrates greater variability than observed between K. crumena and K. thunni, suggest these two species and the case isolate are conspecific and demonstrates the limitatiosn of using LSU in species descriptions.