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Abstract:The estuarine mysid Mesopodopsis tenuipes (Crustacea: Mysida) was often found carrying the peritrich ciliate Zoothamnium duplicatum (Protozoa: Ciliophora) on its body. The prevalence and seasonality of this association were studied on the basis of a year-round survey conducted in the Merbok mangrove brackish water in north-western Peninsular Malaysia from March 2005 to February 2006. The frequency of mysids hosting ciliates varied from 0 to 57.3%, with an annual mean of 17.0%. Juveniles showed a significantly lower prevalence of ciliates than adult mysids. There was no difference in infestation prevalence between the sexes. An epibiotic renewal process could be assessed through observations in breeding females. The infestation prevalence and loads were appreciably lower in the females carrying earlier stages of embryos than in those with developed ones, indicating that zoothamnid ciliates may require two or more days to reach a saturation phase in terms of prevalence when ciliate reproduction is high. This, in turn, suggests that the high moulting frequency of the tropical mysid may inhibit high colonisation pressure by the epibiont. A periodic seasonal trend was not determined, although mysids in lower salinity conditions were more likely to carry epibionts than those at higher salinities.

Epibiosis was studied in dominant mangrove crustacean species in several areas in Malaysia. The observed basibionts were the crustaceans Mesopodopsis orientalis, Acetes japonicus, Acetes sibogae, Acetes indicus and Fenneropenaeus merguiensis and the epibionts found were the protozoan ciliates Acineta branchicola, Lagenophrys eupagurus, Conidophrys pitelkae and Zoothamnium duplicatum. Basibionts from the open sea area (Acetes japonicas) and from a sandy beach of Penang (Mesopodopsis orientalis) showed the lowest epibiont densities. Considering all the colonized anatomical units each basibiont species had a distinct epibiotic distribution and the epibiont species presented a significantly different distribution over each of the basibiont species. In the basibiont M. orientalis a significant difference was observed in epibiotic distribution between populations from different geographical areas. Species sampled on mangrove and offshore areas also differed in this respect The different epibiont species varied among locations according to the structure of the community. We also report on the pattern of epiobiont distribution over the anterioposterior axis of the basibiont, on the influence of physiological characteristics of basibiont and epibiont and on the influence of environmental conditions on the epibiont communities.