Triplefin Treat

Dr Malcolm Francis

Mottled Triplefin

Mottled triplefin Photo: Malcolm Francis

Well-established marine reserves are known for their abundance of large fishes, which thrive in the absence of fishing pressure. Already, the Taputeranga Marine Reserve (TMR) has more, larger and tamer butterfish, blue cod and blue moki than before it was created in 2008. Less obvious, but much more abundant, are the many species of small fishes – most of which are not affected by fishing (at least not directly) and so they do not change in abundance much following protection. But small fishes are ecologically very important on rocky reefs, and contribute hugely to the biodiversity in a marine reserve. Small fishes are often cryptic, or just unnoticed because of their size, but they are fascinating, diverse and well worth getting to know. 

New Zealand excels in triplefins (family Tripterygiidae) – so named because each species has three separate dorsal fins. In fact we lead the world in them – we have at least 26 species of triplefins, and all of them are endemic, occurring nowhere else in the world (apart from three species that have invaded Australia). Of these, at least 17 occur in the TMR. Triplefins are small fishes, with most not exceeding 12 cm in length. However, many species are abundant and they inhabit all hard substrates within the reserve, making them a major component of the fish fauna.  

Banded triple Fin

Banded triple Fin Photo Stephen  Journee

Most triplefins live on or very close to the seabed, often in crevices or under cobbles or boulders. They are usually seen perched on the seabed on their pectoral and pelvic fins. Scientists have found that each one has a unique colour pattern that lasts for years, perhaps for its lifetime, so individuals can be recognised by each other, and by us if we take the time to look for the subtle differences. Triplefins establish territories of a few square metres, and stay there for life. They also have an incredible navigational ability: some variable triplefins (Forsterygion varium) that were displaced more than 700 m from their territories in the Leigh Marine Reserve found their way back home – an extraordinary feat for such a small fish.

Oblique MPF-3
Oblique swimming triplefin    Photo M. Francis

One highly unusual species, the oblique-swimming triplefin (Obliquichthys maryannae), is the world’s only schooling triplefin species. It may form schools of thousands that hover within a few metres of a rock face or reef, usually with the body held at an oblique angle. In the TMR, school sizes are usually much smaller than this, numbering fewer than 50 fish. 

Triplefins range from highly coloured to drab or cryptic. Some species have bright bands on the body (e.g. blue-eyed triplefin Notoclinops segmentatus and mottled triplefin Forsterygion malcolmi) and might appear to be advertising themselves excessively to any passing predator. However these species often inhabit shady rock walls and crevices, or areas under kelp canopies. Here, sponges, ascidians and sea anemones encrust the rocks, providing a richly coloured tapestry into which the triplefins blend without difficulty – they are often only noticed by divers who carefully study the rock walls, or when the triplefin darts from one place to another.

 Blue-eyed male MPF-1

Blue eyed triplefin male Photo: M Francis
Blue eyed tripple fin

Blue eyed triplefin female Photo: Stephen Journee

Some triplefins are specialists in camouflage. The twister and mottled twister (Bellapiscis medius and B. lesleyae) are mottled to merge with the contrasting colours of the rocks and coralline algae of their rock pool and shallow intertidal habitats. The topknot and brown topknot (Notoclinus fenestratus and N. compressus) take camouflage to a higher level with an ability to change their colour and pattern (which ranges from uniform to banded) to match their background. More amazingly they have transparent ‘windows’ in their fins that reveal the seaweed behind them, making them practically invisible. The topknot is further distinguished by being the largest triplefin in the world, reaching at least 22 cm in length.

 Topknot MPF-4

Topknot                        Photo: Malcolm Francis

During the spawning season, which is mainly in winter-spring but may trickle on through most of the year, male triplefins adopt a dramatically different spawning colour pattern. Male variable triplefins change from having a mottled black and cream pattern on the back, and pale belly, to dark grey or black all over; male common triplefins change from a pale colour with a black stripe along the back to jet black all over. Other triplefins may intensify bright colours: the blue-eyed triplefin flushes red-orange on the head and front of the body, and the speckled fawn Yaldwyn’s triplefin (Notoclinops yaldwyni) becomes bright orange. These different colour patterns advertise the male’s breeding prowess and his territory to would-be partners.

Yaldwyn's female MPF-2

Yaldwyn’s triplefin          Photo: Malcolm Francis

Most species of fishes spawn by spraying their eggs and sperm into the water column where fertilisation occurs. The resulting larvae then drift in the open sea for days to months before settling back on to the reef to begin life as juvenile fishes. Triplefins don’t do this. Males establish territories that contain nesting sites, and then proceed to attract females to spawn there. A female deposits her sticky eggs on a rock or in a shell, and the male immediately fertilises them with his sperm. He then guards the eggs, defending them from predators and aerating them by maintaining water circulation with his fins. They hatch out 1–2 weeks later as well developed larvae and join the plankton of the open sea. Triplefins only produce small numbers of young, but by protecting them through the vulnerable egg and early larval stages, their survival chances are greatly enhanced.  

Next time you are diving in the TMR, take some time to sit or hover in one place and watch the triplefins come out from cover and start ‘hopping’ around their territories. Some species will move out into the open, but you should also carefully search rock walls, under overhangs and at the base of rock walls for the cryptic species that blend in with their surroundings. Triplefins may not be big, but they are important, spectacular, and have a fascinating suite of behaviour patterns.  

See more triplefins in Malcolm’s recently revised ‘Coastal Fishes of New Zealand’ 4th Edition, 2012, Craig Potton Publishing,