Blackthroat Threefin

Interesting Info

• The Blackthroat Threefin is a tiny reef fish, you’ll find them in southern and western Australia, from South Australia’s gulf waters to Western Australia’s coast – hiding amongst algae and rocks.
• It has three dorsal fins, like other triplefins, plus ring-like scales and a distinctive black throat patch in males.
• In males the upper body is yellow-green and the underside is jet-black—especially vibrant during courtship or when defending territory.
• Females are well camouflaged—reddish or greenish mottled bodies with subtle blotches and a dark patch under the eye.
• They live in very shallow water, mostly within 0–15 m (0–50 ft). Often under ledges, in crevices, or over rock surfaces near jetty piles and reefs.
• Males fiercely guard small reef territories against rivals, showing off their high-contrast colours as a warning.
• Females lay sticky eggs on algae or rock, which the males then guard until hatching.
• They’re one of the most common small fishes in their habitat, but because they’re cryptic and tiny, snorkelers and divers often miss them, unless they know what to look for.
• Predators include small wrasses and dottybacks such as hulafish, which pick off triplefins darting among algae and rubble.
• They act like mini-cleaners for the reef—eating micro-invertebrates and tiny algae to help keep surfaces clear.
• Their name ‘decurrens’ hints at their sloping black throat—”that runs down” like a paint drip.