ABSTRACT: Experiments were conducted to: (1) test the response of oysters to different doses of the oyster parasite Perkinsus marinus and to 2 stages, meronts or prezoosporangia; and (2) investigate the synergistic effects of temperature, salinity and infective cell concentration on P. marinus infection in oysters. A dose-dependent response of P. marinus infection was found in oysters inoculated with 0, 10, 10², 10⁴, and 10⁵ meronts or prezoosporangia per oyster and maintained at 22 to 25°C and 14 to 21 ppt for 8 to 12 wk. The minimum dose required to infect oysters was 10² meronts or prezoosporangia per oyster through shell cavity inoculation. Interactive effects between temperature, salinity, and infective cell dose on P. marinus prevalence was insignificant in the experiment, in which oysters were challenged by 0, 2.5 [lozenge] 10³ or 2.5 [lozenge] 10⁴ meronts per oyster and held at 9 temperature-salinity regimes (10, 15 and 25°C at 3, 10 and 20 ppt). However, there was a significant positive interaction relevant to infection intensity between temperature and salinity, and between temperature and meront dose. Temperature was the most important factor followed, respectively, by the infective cell dose and salinity in determining the susceptibility to P. marinus in oysters. Reduced condition index was observed in moderately to heavily infected oysters and in oysters at 25°C.

KEY WORDS: Oyster · Crassostrea virginica · Oyster parasite · Oyster disease · Perkinsus marinus · Temperature · Salinity

Published in DAO Vol. 28, No. 1 (1997) on January 16
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1997