Population model for Amyloodinium ocellatum infecting the spotted seatrout Cynoscion nebulosus and the red snapper Lutjanus campechanus.

The dinoflagellate Amyloodinium ocellatum, a major pathogen in warm water mariculture, has a trophont, a tomont and a dinospore life history stage. This paper presents a population model for A. ocellatum infecting spotted seatrout Cynoscion nebulosus and red snapper Lutjanus campechanus and evaluates the relative effect of each vital rate on the A. ocellatum population growth rate. The vital rates were estimated by incubating trophonts in vitro and tracking their development through the successive life history stages at 25°C and 33 ppt. The A. ocellatum population growth rate was 1.90 d-1 for spotted seatrout and 1.92 d-1 for red snapper. Highest elasticity values (0.24 and 0.23 in spotted seatrout and red snapper, respectively) corresponded to transitions from the dinospore to the trophont stage, the trophont stage to the tomont stage and the tomont stage back to the dinospore stage in both host species (self-loops not included). A 50% change in vital rates showed that the mean number of dinospores produced by a tomont had the largest effect on the A. ocellatum population growth rate (15%), followed by the dinospore infection rate (14%), the tomont sporulation rate (12%) and the dinospore mortality rate (10%) in both host species. A comparison of modeled and experimental vital rate threshold values revealed a 2.5- (spotted seatrout) or a 2.6-fold (red snapper) difference in the values for dinospore mortality, which is the smallest difference among all the modeled and experimental vital rates. Therefore, measures that increase dinospore mortality have a greater likelihood of influencing the outcome of an epidemic.