Dimension, Prevalence, Intensity and Histopathology of Octolasmis sp. on Blue Swimming Crab from Bulusan Beach, Banyuwangi Regency, Indonesia

The blue swimming crab Portunus pelagicus is an economically important species in tropical waters, particularly in Indonesia. This study aimed to investigate the prevalence, intensity, and pathological effects of the ectoparasite Octolasmis angulata on P. pelagicus at Bulusan Beach, East Java, during October to November 2024. Morphological identification and histopathological analyses of 12 specimens revealed that O. angulata attachment caused severe respiratory impairments, as evidenced by disrupted gill lamellae and hemocytic responses. A strong positive correlation was observed between crab size and infestation level, suggesting that larger crabs were more susceptible to heavier O. angulata colonization. Infestation analysis showed that O. angulata exhibited a marked preference for the gills, with 2,081 individuals recorded, compared to 205 on the carapace and 43 on the pereiopods. Histopathological examination of the gills revealed extensive structural damage, including lamellar fusion, vacuolization, and hemocyte aggregation, emphasizing the detrimental effects of O. angulata on host respiratory function. These findings provide new insights into the infestation dynamics and pathological implications of O. angulata in P. pelagicus, contributing to a better understanding of host–epibiont interactions in tropical marine ecosystems.