First records of two peritrich ciliates: <i>Epistylis</i> and <i>Zoothamnium</i> as epibionts of freshwater copepods in the Philippines

Copepods are known to have symbiotic relationships with protozoan organisms with significant parasitic or commensal associations with their adult or juvenile copepod hosts. However, taxonomic studies and distributional records of microcrustaceans and their symbionts remain incomplete in the Province of Sorsogon in the Bicol Region, Philippines. To address this knowledge gap, samples were collected from 19 sampling sites across Sorsogon Province across different freshwater bodies. Thermocyclops taihokuensis was the dominant cyclopoid copepod species in the epibiont-infested areas. Protozoan ciliates were prevalent in copepodites with an infestation rate of 0.27% (2 out of 747 copepodites examined). Epistylis niagarae were abundant on the urosome of a C5 copepodite from the Gogon reservoir site. While Zoothamnium sp. epibionts were dominant in the prosome of a C2 copepodite from an irrigation canal at the Prieto Diaz site. Both sampling sites are near potential habitats of freshwater fish for aquaculture. The findings of the preliminary survey provided the first accounts of copepod-epibiont interactions in Sorsogon’s inland freshwater bodies. The study also served as the first record of Zoothamnium and Epistylis ciliates as epibionts of copepods in the Philippines. The output of this analysis could contribute to more freshwater biodiversity studies in the Bicol region, promoting a holistic approach to exploring host-symbiont relationships in aquaculture habitats.