Experimental Population Dynamics of Amyloodinium ocellatum in the Spotted Seatrout, Cynoscion nebulosus, and the Red Snapper, Lutjanus campechanus

Ignacio Masson


Amyloodinium ocellatum is a parasitic dinoflagellate that infects warm water marine bony fishes and causes high mortalities in aquaculture settings. It has three life history stages: the feeding trophont, the reproductive tomont, and the infective dinospore. This dissertation describes the characteristics of A. ocellatum infections in juvenile spotted seatrout, Cynoscion nebulosus , and red snapper, Lutjanus campechanus , studies the survival and fecundities of the stages in the life cycle of the parasite and presents a population model for A. ocellatum . At 25°C and 33 ppt, the peak of trophont detachment occurred on day 2 post-infection in spotted seatrout and day 3 in red snapper. Trophont mean length at detachment was significantly larger in red snapper than in spotted seatrout (80 versus 72 μm, respectively), which translates to an increased mean dinospore production in red snapper (99 dinospores tomont -1 versus 82 in spotted seatrout). There was no difference either in the dinospore infection rate (0.36 and 0.34 dinospores d-1 for spotted seatrout and red snapper, respectively) or in the dinospore lethal dose (237,243 and 141,010 dinospores fish-1 for spotted seatrout and red snapper, respectively) between host species, but the mean trophont lethal load was higher in spotted seatrout (178,067 trophonts fish -1 ) than in red snapper (123,160 trophonts fish-1 ) suggesting that the red snapper is less tolerant of A. ocellatum infections than spotted seatrout. The mean number of offspring per generation per individual for A. ocellatum (R0 ) was 49.15 dinospores tomont-1 with a generation time of 6.3 d. These rates were estimated using the mean tomont size for infections in spotted seatrout. Analysis of the population model revealed that changes in the mean number of dinospores tomont -1 had the largest effect on A. ocellatum population growth, followed by the dinospore infection rate, the tomont sporulation rate and the dinospore mortality rate. A higher A. ocellatum population growth rate was observed in infections in red snapper than in spotted seatrout. These studies elucidate the dynamics of the life cycle of A. ocellatum and demonstrate the critical life cycle control points at which management strategies can be focused.