Variable Threefin

Interesting Info

• The Variable Threefin is a small triplefin fish that grows up to about 13 cm (5 in).
• It gets its name from its three dorsal fins lined up in a row—one of the trademarks of the triplefin family.
• Males are brightly patterned with vivid bands and colours, while females are mottled brown and camouflaged against rocks.
• The species is native to New Zealand but has been introduced to Tasmania, likely through oyster farming in the mid-20th century.
• They live in shallow reef areas and tide pools, usually from the surface to about 30 m (100 ft).
• Variable Threefins are habitat generalists—found in rocky reefs, tide pools, wharf piles, seagrass beds, and kelp forests.
• They feed on tiny crustaceans, worms, and small invertebrates they pick off reef surfaces.
• Males guard sticky egg clutches laid by females on rocks, fanning them with their fins to keep them oxygenated until hatching.
• During breeding season, males become especially bright and aggressive, defending nests from rivals.
• They grow quickly and usually live around 4 years, though some may survive up to 5–6 years in good conditions.
• They are one of the most abundant small fishes in New Zealand’s tide pools and rocky reefs, sometimes carpeting habitats in huge numbers.
• Because of their small size, they are preyed on by larger reef fishes, seabirds, and other coastal predators.
• Variable Threefins help transfer energy through the reef ecosystem—eating small plankton and invertebrates, and then being eaten by bigger predators.
• They are often overlooked by snorkelers and divers because of their size, but once spotted they’re one of the most common reef residents.