Abstract: The dragonet family Callionymidae comprises a group of fishes widely distributed in temperate to tropical marine waters worldwide, many of which are important commercial or aquarium fish. In this study, we confirm the presence of the smallhead dragonet, Callionymus erythraeus, in the coastal waters of Hailing Island, Yangjiang City, Guangdong Province, China via morphological identification and molecular identification based on the mitochondrial COI marker, which represents the first record of this species from Chinese waters. Compared to other co-occurring species within the family, this species can be distinguished by several unique morphological characteristics. Males possess an enlarged first dorsal fin with filamentous spines, among which the fourth spine is notably the longest. The dorsal, caudal, and pelvic fins display distinctive brown reticulate patterns. The body exhibits a reddish-brown coloration on the dorsolateral region, transitioning sharply to white on the ventral side along a jagged boundary. Numerous small white spots are densely scattered between the upper boundary and the lateral line, while larger white spots are present on the flanks. White, saddle-shaped blotches are visible at the base of the dorsal fin. The COI gene sequence obtained from the study is 1521 bp in length, with a genetic distance of 0.0030 from the C. erythraeus reported from Singapore, indicating intraspecific variation. Our findings not only add a new species to the checklist of Chinese dragonets but also contribute to the understanding of the country's marine fish biodiversity.

Key words: smallhead dragonet, new-record species, Syngnathiformes, COI barcoding, China