Impact of Perkinsus sp. on Manila clam Ruditapes philippinarum beds

Abstract

Three million Manila clams (Ruditapes philippinarurn, Adams & Reeve 1850) were sown in 3 sets: A, B and P (0.65, 0.66 and 0.79 g per clam respectively) in intertidal beds of the Eo estuary (Asturies, N Spain). In January 1994 Perkinsus sp. was detected in set P. Growth, survival and prevalence of Perkinsus sp. were periodically examined during a 2 yr period. Clam growth and survival were unaffected by the parasites in all sets, probably due to the low prevalence of Perkinsus sp. (which ranged from 2 to 9%). This low prevalence, in turn, may have been due to the fact that water temperature remained below 20C. We suggest that, in most cases, clam mortality associated with Perkinsus sp. may be minimized with adequate management of clam beds. The disease could be controlled if stressful growing conditions such as high densities, harvesting, or overcrowding in depuration plants are avoided during the warmer months. Additionally, we recommend 2 prophylactic measures: the removal of sets with parasitized clams and the introduction of unparasitized seed in clam culture areas.