Impact of Perkinsus sp. on Manila clam Ruditapes philippinarum beds.
The relationship between Perkinsus sp. and the growth and survival of Manila clams (Ruditapes philippinarum) was investigated over a 2-year period. In June 1993, 3 million Manila clams were sown in 3 sets: A, B and P at a mean weight of 0.65, 0.66 and 0.79 g/clam, respectively. The sets were planted in sand-gravel, intertidal beds of the Eo estuary (Asturias, northern Spain). Bi- or trimonthly clam samples were collected between June 1993 and August 1995. In January 1994, Perkinsus sp. was detected in set P. The growth rates of unparasitized clams in sets A and B were similar to the growth rates of infected clams in set P. This was probably due to the low prevalence of Perkinsus sp. (which ranged from 2 to 9%), which in turn, may have been due to the fact that water temperature remained below 20°C. It is suggested that, in most cases, clam mortality associated with Perkinsus sp. may be minimized with adequate management of clam beds. Additionally, 2 prophylactic measures are recommended: the removal of sets with parasitized clams and the introduction of unparasitized seed in clam culture areas.