Leeches on mudskippers: host-parasite interaction at the water's edge

Fish ectoparasite detection, collection and curation

Fish parasitology is a dynamic and internationally important discipline with numerous biological, ecological and practical applications. We reviewed optimal fish and parasite sampling methods for key ectoparasite phyla (i.e. Ciliophora, Platyhelminthes, Annelida and Arthropoda) as well as recent advances in molecular detection of ectoparasites in aquatic environments. Ideally, fish capture and anaesthesia as well as parasite recovery methods should be validated to eliminate potential sampling bias and inaccuracy in determining ectoparasite population parameters. There are considerable advantages to working with fresh samples and live parasites, when combined with appropriate fixation methods, as sampling using dead or decaying materials can lead to rapid decomposition of soft-bodied parasites and subsequent challenges for identification. Sampling methods differ between target phyla, and sometimes genera, with optimum techniques largely associated with identification of parasite microhabitat and the method of attachment. International advances in fish parasitology can be achieved through the accession of whole specimens and/or molecular voucher specimens (i.e. hologenophores) in curated collections for further study. This approach is now critical for data quality because of the increased application of environmental DNA (eDNA) for the detection and surveillance of parasites in aquatic environments where the whole organism may be unavailable. Optimal fish parasite sampling methods are emphasised to aid repeatability and reliability of parasitological studies that require accurate biodiversity and impact assessments, as well as precise surveillance and diagnostics.

Population Genetic Structure of Marine Leech, Pterobdella arugamensis in Indo-West Pacific Region

Grouper aquaculture is rapidly expanding in both tropical and subtropical regions. The presence of marine leeches (Pterobdella arugamensis; previously named Zeylanicobdella arugamensis) infesting cultured groupers, however, can have a fatal effect on grouper aquaculture production and cause significant economic loss. Understanding the marine leech’s population structure is therefore important to determine its possible distributional origin and distributional mechanisms, which will help monitor and mitigate the infestation. In this study, a total of 84 marine leeches collected from cultured hybrid groupers Epinephelus spp. in Brunei Darussalam, Malaysia and Indonesia were identified as P. arugamensis, based on morphological and mitochondrial cytochrome c oxidase subunit I gene sequence analyses. These leech samples, together with additional sequences from the GenBank database, were grouped into four genetically distinct haplogroups: (1) Asia Pacific, (2) Borneo, (3) Surabaya and (4) Iran. The four populations were found to be highly diverged from each other. The results also suggested that the samples from the Asia Pacific population could be dispersed and transported from Indonesia.