Littoral Water in Hong Kong as a Potential Transient Habitat for Juveniles of a Temperate Deepwater Gnomefish, Scombrops boops (Acropomatiformes: Scombropidae)

A total of 40 juveniles belonging to a temperate deepwater gnomefish species, Scombrops boops, were sampled from littoral habitats (2-5 m depth) of eastern Hong Kong waters in April and May 2017 and March 2019. The presence of gnomefish juveniles in subtropical southern China is reported for the first time at a record low latitude of 22°11'-22°21'N. The specimens were identified based on the COI gene sequence. The genetic composition between Japan and Hong Kong gnomefish populations were compared by sequencing the mitochondrial Cytb gene, which showed no genetic differentiation. The juveniles ranged from 3.5-10.1 cm (n = 40) in total length, with 35 individuals caught from Sargassum beds and five from rocky reefs. Our findings highlighted that the littoral habitats in Hong Kong waters, in particular the seasonal Sargassum beds, are important for small juveniles of S. boops.