The trypterigids are a large family of about 130 species, which resemble the blennies but have three dorsal fins and relatively large scales. Male black-throated threefin have a yellow upper and black lower colouration, which is accentuated when defending territory or displaying for a female. Females remain well camouflaged possessing a lighter-coloured body with mottled red, brown and yellow colouration with feint banding. The black-throated threefin grow to a maximum length of 7 centimetres.
The black-throated threefin is an abundant fish species in southern Australian coastal waters, inhabiting shallow rocky reef in crevices, on rock faces and among jetty piles to depths of 15 metres. They occur from Point Quobba, WA to Victor Harbour, SA. Due to their small size and cryptic nature they are not often noticed by divers.
Other common names include: Yellowback threefin, blackthroat threefin, black-throated threefin, black-throated triplefin, gulf threefin, southern triplefin, threefin, yellowback threefin.
Occurrence at the Busselton Jetty:
Black-throated threefin are always present on the invertebrate adorned piles of the Busselton Jetty, one just needs a good eye to be able to spot them. The males duel colouration and the females mottled colouration makes them one of the most cryptic fish species, as they blend into their colourful surroundings. It’s often not until they move to another resting position where they remain propped up on their ventral fins that they may be spotted.