Infection dynamics of Kudoa inornata (Cnidaria: Myxosporea) in spotted seatrout Cynoscion nebulosus (Teleostei: Sciaenidae).

Kudoa inornata is a myxosporean parasite that develops in the somatic muscle of spotted seatrout Cynoscion nebulosus, an economically and ecologically important fish in estuaries and harbors in southeastern North America. In South Carolina (SC), USA, over 90% of wild adult spotted seatrout are infected. To inform potential mitigation strategies, we conducted 3 experiments using naïve sentinel seatrout and infectious stages of K. inornata naturally present in raw water from Charleston Harbor, SC, to determine (1) if K. inornata infection follows a seasonal pattern, and (2) how long it takes for myxospores to develop in fish muscle. Infection by K. inornata was determined by visual detection of myxospores in fish muscle squashes, and any visually negative samples were then assayed for K. inornata ribosomal DNA using novel parasite-specific PCR primers. We observed that K. inornata infection in seatrout followed a seasonal pattern, with high prevalence when water temperature was highest (27-31°C; July-September) and infections that were either covert (at ~13-15°C) or not detected (<13°C) at the lowest water temperatures in January-February. Myxospore development occurred within 476 degree-days, i.e. 2 wk in a typical SC summer. Infection was dependent on fish density, which limited presumptive actinospore dose. Our findings suggest that the life cycle of the parasite may be disrupted by preventing spore-rich seatrout carcasses (e.g. at angler cleaning stations) being thrown back into harbors and estuaries throughout the year.