Occurrence of the epibiont Octolasmis spp. in the mud crab (Scylla serrata) in the Bons Sinais Estuary

The genus Octolasmis comprises ectoparasites frequently associated with crabs, whose prevalence and intensity of infestation are relevant indicators of the health of host populations. This study aimed to determine the prevalence, intensity, and seasonal variation of infestation by epibionts of the genus Octolasmis in Scylla serrata in the Bons Sinais estuary. 157 individuals collected between June and July (corresponding to winter) and between October and November 2025 (corresponding to summer) were analyzed, obtaining 76 individuals in winter and 81 in summer. In the laboratory, biometric analysis of the specimens and separation by sex were performed; each crab was measured for carapace length and width and body weight. Subsequently, the epibionts were identified through visual observation of the external and internal surfaces of the crabs, and the number of infested crabs was counted. After counting the epibionts, they were placed in a Petri dish and observed under a stereomicroscope for taxonomic identification, which was performed based on observation of morphological characteristics. Two species were identified, Octolasmis angulata and Octolasmis cor, with Octolasmis cor being the most predominant (61.8%). The overall prevalence of Octolasmis in the Bons Sinais estuary was moderate; no marked seasonal variation in prevalence was observed, with a prevalence of (32.8%) in winter and (37%) in summer, with no statistically significant difference between the seasons (p>0.05). In winter, the average intensity was (75.2) epibionts per host, and (32.3) in summer, with a statistically significant difference (p<0.05). Regarding sex, males showed a higher prevalence (41.2%) and intensity of (47.2) epibionts per host, while females showed (28.5%) and (48.2), respectively. A weak but statistically significant positive correlation was found between carapace width and the number of epibionts (p< 0.05), suggesting that larger crabs tend to have a higher epibiont load, although the relationship is weak.

It is concluded that Octolasmis infestation in Scylla serrata occurs moderately in terms of prevalence but can reach high levels of intensity that are worrying from an ecological and economic point of view, especially in winter, with potential implications for the health of the host and the commercial value of this fishery resource.