Seasonal Distribution and Host-Parasite Interaction of Pedunculate Barnacle, Octolasmis spp. on Orange Mud Crab, Scylla olivacea

Seasonal distributions of pedunculate barnacles, Octolasmis spp. on mud crab (Scylla olivacea) were investigated. Each ten specimens of male and female crabs were monthly collected from crab farms in Kan-Tung District, Trang Province, Southern Thailand (Andaman Coast). Live crab specimens were examined for gill parasites throughout 12 months (March, 2010 to February, 2011). The parasites found from each gill of crab samples were dislodged, examined and directly counted. The seasonal distribution pattern of gill parasitic populations was proposed and the interaction between host and parasite (size, sex) was also determined using an existing statistical program. Almost all crab samples (97 %) were infested with pedunculate barnacles of the genus Octolasmis (Cirripedia: Poecilasmatidae). Female crabs showed higher loading capacity for parasites than the male ones indicating by their intensities, 125: 47 specimens / crab host (p 0.05). The seasonal changes influenced parasitic abundance, with low numbers present in the rainy season (July and October, 2010 and January - February, 2011). It could be concluded that the pedunculate barnacles’ population reflected their limited tolerance of water salinity caused by seasonal variation