DAO 50:51-65 (2002)  -  doi:10.3354/dao050051

ABSTRACT: Morphological characters of zoosporulation stages and DNA sequence of the internal transcribed spacer (ITS) region and the small subunit ribosomal RNA (SSU rRNA) gene confirmed that the aetiological agent of perkinsosis in the clam Tapes decussatus from Galicia (NW Spain) was Perkinsus atlanticus Azevedo, 1989. In vitro modulation by temperature and salinity of the zoosporulation of the parasite was studied. The optimum temperature range for zoosporulation was 19 to 28°C. The temperature range allowing zoosporulation in vitro was 15 to 32°C, which is broader than previously reported (24 to 28°C) for P. atlanticus, and strongly suggests that zoospores can be produced in Galician Rías, where temperature ranges from 10 to 22°C. Prezoosporangia held at 10°C for 2 mo (similar to winter conditions in Galician waters) gave rise to viable zoospores after they were transferred to higher temperatures. This suggests that prezoosporangia could overwinter and zoosporulate in the next spring. Zoospores could survive for up to 22 and 14 d at 28 and 10°C, respectively. The optimum salinity range for zooporulation was 25 to 35‰. Zoospore production was abruptly reduced as salinity decreased. The lowest salinity at which zoosporulation was observed was 10‰. The effectiveness of different chlorine concentrations and exposure lengths to kill prezoosporangia and zoospores was tested. No survival of free zoospores, free prezoosporangia and prezoosporangia included in gill tissue was observed after incubation for 1 h with 50, 200 and 3000 ppm of chlorine, respectively.

KEY WORDS: Perkinsus atlanticus · Tapes decussatus · SSU rRNA gene · ITS region · Zoosporulation · Ultrastructure · Temperature · Salinity · Chlorine