The sargassum frogfish (Histrio histrio Linnaeus, 1758) belongs to the family Antennariidae and the genus Histrio. In June 2013, researchers from the Marine National Park Headquarters (MNPH) discovered this species within the seagrass beds near the lagoon mouth on the western shore of Dongsha Island. After verification, it was confirmed as a new fish record for Dongsha Atoll National Park.

New fish record for Dongsha — Sargassum frogfish (Histrio histrio) (Photo by Chiang Chun-ting)

The sargassum frogfish can reach a maximum length of about 20 cm. It commonly inhabits coral reef areas from the intertidal zone to subtidal waters, attaching itself to underwater structures or floating seaweed. Its body coloration is highly variable and can effectively mimic its surrounding habitat. Members of the frogfish family have specialized pectoral and pelvic fins that resemble toes, enabling them to cling to seagrass or floating debris, or even “walk” along the seafloor. When moving, the pectoral fins, pelvic fins, and tail fin simultaneously touch the substrate, giving the appearance of having five legs. For this reason, Taiwanese fishers often refer to them as the “five-legged tiger.”

Although its appearance may seem amusing and cute, the sargassum frogfish is a formidable ambush predator. Its first dorsal spine is modified into an “illicium,” a fishing rod-like appendage tipped with a lure that can wiggle like bait. Unsuspecting small fish or crustaceans are attracted to the movement, only to be swiftly engulfed by the frogfish’s large mouth. As a highly carnivorous species, the nickname “tiger” is indeed well deserved.

Dongsha Atoll National Park encompasses a wide variety of marine habitats and rich biodiversity. The discovery of the sargassum frogfish in the seagrass beds near the inner lagoon marks the second frogfish species recorded in the park. The previously recorded species — the painted frogfish (Antennarius pictus) — primarily inhabits coral rubble around Dongsha Island and displays vivid coloration that mimics coral reef environments. In contrast, the sargassum frogfish prefers seagrass beds and floating algae, with body coloration adapted to resemble drifting seaweed and plant debris. The divergent ecological adaptations of closely related species occupying different habitats present a fascinating example of evolutionary specialization. How many more members of the “five-legged tiger” family inhabit the vast and mysterious waters of Dongsha Atoll National Park remains to be discovered through continued research and exploration.

The sargassum frogfish, nicknamed the “five-legged tiger,” looks quite charming when walking on the seafloor. (Photo by Chiang Chun-ting)	Floating seaweed and marine debris are primary habitats of the sargassum frogfish. (Photo by Liao Chen-heng)