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This study reports on diseased Chelidonichthys spinosus fish that were originally obtained from the Taiwan Strait for exhibition in an aquarium. These fish showed abnormal swimming behavior, eye damage and skin lesions. Gross examination and histopathology revealed that the C. spinosus was suffering from severe nematode infections in the pyloric caeca, liver and mesentery. Marine nematodes from internal organs were verified by partially sequencing the internal transcribed spacer (ITS) gene. Sequencing results revealed that the nematodes shared 99.75% sequence identity with Raphidascaris lophii (GenBank accession No. MW132926). Additionally, secondary Vibrio harveyi infections were also detected in some C. spinosus. This is the first report of R. lophii infection in C. spinosus.

Non-point source microbial pollution damages the overall health of marine ecosystems. Beyond their direct effects, contaminating microbes can introduce antimicrobial resistance and virulence genes into resident species by horizontal gene transfer, a process that may be enhanced by co-pollutants such as heavy metals. In this work, a number of heavy metal- and antimicrobial-resistant (AMR) strains of E. coli were isolated from water and sediment samples collected in the Causeway Bay, Hong Kong (22.2833 N, 114.1847 E) and their complete genomes obtained by hybrid assembly using both Illumina MiSeq and Oxford Nanopore MinION sequencing platforms. Genomic analysis showed an abundance of plasmids and mobile elements bearing heavy metal- and AMR genes, such as the mer operon and tetR-tetA efflux system, with these features frequently co-located. In addition, NCBIBLAST–using isolates collected from in-land soil, freshwater, and animal faeces in Hong Kong, as well as the NCBI database – showed that these genes, while common amongst human and animal-derived Enterobacteriaceae, could also be shown present in a number of strains of obligate halophilic Vibrio spp.. Previous water chemistry analysis at this location showed high levels of heavy metal contamination (98 ppm Pb, 0.12 ppm Hg, and 0.4 ppm Cd), which has been shown to promote AMR transfer by selecting for co- resistance. Further isolation and characterisation of marine bacterial species from Hong Kong coastal waters will help to determine the extent of this process.