Triplefin fishes (family Tripterygiidae) are the most abundant of New Zealand’s shallow-water subtidal reef fish. It is thus surprising that they are so poorly known by most New Zealanders, who refer to them simply as cockabullies or blennies. Blennies are in fact a distinct group (family Blenniidae). Both triplefins and blennies are small fish that lack swim bladders as adults, but triplefins are characterised by having three dorsal fins and scales on the sides of the body, while blennies have one continuous dorsal fin and lack scales. Only one species of blenny the crested blenny (Parablennius laticlavius)—is common in New Zealand coastal waters.
Approximately 30 genera and 130 species of triplefin have been identified worldwide, in tropical, subtropical, temperate, subantarctic and—in the case of one species recorded from the Antarctic Peninsula—polar seas. But triplefins reach their greatest diversity and size in the New Zealand region, and are the most characteristic and ubiquitous feature of the New Zealand coastal fish fauna. It is no exaggeration to say that triplefins are as iconic among New Zealand fishes as weta are among New Zealand insects and kiwi among New Zealand birds.
The New Zealand triplefin fauna includes 14 genera and 26 species, and thus constitutes a significant proportion of triplefin diversity worldwide. What is even more surprising is that 12 of these genera and all 26 species are unique to New Zealand, except for three species accidentally introduced to Australia. Just two species—the ocellate triplefin (Apopterygion oculus) and the Kermadec triplefin (Enneapterygius kermadecensis)—have close evolutionary affinities to fishes elsewhere. The latter species is endemic to the Kermadec Islands and belongs to a genus of tropical species.
This level of endemism is approximately ten times that of the New Zealand marine-fish fauna as a whole. How it has arisen is an interesting biological question. Are the seas around New Zealand some kind of living museum for triplefins, a refuge where relic species hang on like aquatic tuatara? Preliminary DNA evidence suggests not. New Zealand species seem generally to be closely related to one another, suggesting that most have radiated from an ancestral species over the last 12–25 million years.
Of the 26 species of triplefin known in the New Zealand region, 21 are found on rocky reefs, one in‑habits intertidal rock pools, three are deep-water denizens, and one lives in estuaries and river mouths.
The five non-reef species include two triplefin world records: the only species that lives in brackish water (the estuarine triplefin, Grahamina nigripenne), and the world’s deepest-living triplefin (the Chatham deep-water triplefin, Matanui bathytaton, which has been collected at depths in excess of 500 m).
All 20 species of temperate rocky-reef triplefin are found from Stewart Island to North Cape. None displays obvious latitudinal trends in abundance, although, like many reef fishes, they all grow larger in cooler, southern waters. This broad distribution is unusual, as most species of coastal New Zealand fish are either distinctly northern or distinctly southern. However, there are gaps in the distribution of some species; for instance, several have not been recorded from the north-west of the South Island. These gaps appear to relate to patterns of dispersal of the planktonic larvae (see below) and the absence of specific habitats in certain areas.
That most species occur around the whole country poses another puzzling question. New species generally arise from populations that have become reproductively isolated following geographical separation. For instance, a powerful storm might pick up some Australian insects and deposit them a few days later in Taranaki, where environmental conditions differ from those to which they are adapted. Being unable ever to travel upwind back to Australia, they adapt to their new environment, evolving to such an extent that they eventually become a new species. In marine environments, geographic isolation doesn’t come about quite so readily, but is still thought to be the main route to speciation.
Here, then, is the puzzle: most New Zealand triplefin species evolved from a common ancestor, yet are found throughout New Zealand waters. There is thus no evidence from current species distribution patterns for the geographic isolation that normally precedes speciation. Did some of the New Zealand triplefin species evolve in geographically continuous populations? Our research seeks to answer this question.
As part of this project, my graduate students and I have searched for and studied triplefins throughout New Zealand seas for a number of years. The most elusive species has proved to be the ocellate triplefin (Apopterygion oculus). This was described only in 1994, and most specimens had been taken in dredges from deep water. The literature suggested that A. oculus was found on shell rubble at the lower depths to which divers descend (although specimens had been found in less than 10 m in southern New Zealand). I had surveyed this habitat for years in a number of places, including the sea around Wellington and in Fiordland, without success.
In April 2004, I visited Stewart Island with a research party and went to a spot off Vaila Voe, in Patterson Inlet, where specimens had been collected in 1954. The water was 11 m deep and the sea-floor composed of silty sand with patches of drift seaweed. Almost immediately I saw a small ocellate triplefin sitting on the sand at the edge of a patch of seaweed, and caught it. Within a very short time I found another, and then another; in fact, they were so numerous that PhD student Maren Wellenreuther made some abundance counts. I took several photographs, the only images of living specimens I’ve seen. I suspect A. oculus prefers silty habitats in cool water, and in more northern locations would be found in deeper water.
Despite their abundance and therefore their importance to the ecology of rocky reefs in New Zealand seas, triplefins have been little studied compared with other reef fishes, such as snapper, wrasses and moki. This is probably due to the taxonomic confusion that has surrounded the group until recently, confusion caused by close resemblances between species and variability in colour patterns. Graham Hardy, at the Museum of New Zealand in the 1980s, and to a lesser extent the German scientist Ronald Fricke, in the early 1990s, sorted out the naming and identification of most species. Much pioneering work on the ecology of reef triplefins in New Zealand has been carried out at the University of Auckland’s marine laboratory at Leigh by masters students, including Gordon Anderson, Christine Handford, Sue Thompson, Sean Connell, Craig Syms and David Feary. This work forms the core of our understanding of triplefin ecology on rocky reefs in New Zealand.
All New Zealand species of reef triplefin studied to date spend their adult lives within a fairly small area of reef. Tagging studies have shown that individual fish will return to their home rock-pool if released a short distance from the point of capture. Triplefins are sedentary and are normally seen sitting on the substratum propped on their thread-like ventral fins. They tend to move in short hops by pushing off with these fins and steering with their pectoral fins, but when disturbed or chasing prey they are capable of rapid bursts over a greater distance. Triplefins can hold position even in extremely surgy conditions. They face into the flow and press body, ventral fins and anal-fin rays against the substratum while splaying their pectoral fins. The thickened, finger-like lower pectoral rays they angle forwards and brace against the substratum, while the upper rays form a seal against the body.
Most species of triplefin feed on a wide variety of small invertebrates, especially the small crustaceans known as amphipods. (Sand-hoppers, familiar to beach-goers, are amphibious members of the amphipod group.) The catholic nature of the triplefin diet is reflected by the unspecialised form of the jaws and teeth in all but a couple of species. The diet of most appears to reflect the habitat in which they live rather than any food preferences per se. For example, dominant among the prey of seaweed-dwelling triplefins, such as yellow-black (Forsterygion flavonigrun), common (F. lapillum) and variable triplefins (F. Varium), are caprellid and gammarid amphipods that also live in seaweed. Mottled (Grahamina capito) and robust (G. gymnota) triplefins take small crabs as well as amphipods, and items such as small snails, polychaete worms, brittle-stars, fish eggs and small hermit crabs also feature in the diet of many species.
Only a few species of reef-dwelling triplefin studied so far appear to have a somewhat specialised diet, these being giant triplefins, mottled twisters and oblique-swimming triplefins. Giant triplefins (Blennodon dorsale) appear to feed mainly on small mussels, which they prise off the rocks with their large, curved, incisiform teeth. Mottled twisters (Bellapiscis lesleyie) eat small encrusting invertebrates characteristic of the surge zone, such as small chitons and barnacles (the latter’s feeding appendages, or cirri, at least). Oblique-swimming triplefins (Obliquichthys maryannae) feed mainly on planktonic crustaceans such as copepods, although they sometimes forage on animals living on the substratum.
The feeding behaviour of triplefins is simple: prey is approached in a dart and engulfed whole. Species that inhabit rock-pools appear to feed mainly on the rising tide and at high tide. Oblique-swimming triplefins feed in much the same way as other planktivorous fishes, such as blue maomao, by facing into the current and snapping at passing food items. Topknots (Notoclinus fenestratus) ambush small animals while hiding among seaweed. While they enjoy a diet dominated by crustaceans, they have also been observed taking other triplefins.
In northern New Zealand, triplefins live for only two to three years, although in cooler southern waters they may survive for five. Juvenile fish grow rapidly and reach sexual maturity by the end of their first year. Reproductive behaviour commences in autumn, when males assume breeding colouration. In most species this involves a darkening of the usual colour pattern, but there may be other changes. For instance, common, variable, banded, mottled, spectacled (Ruanoho whero) and long-finned (R. decemdigitatus) triplefins develop an almost jet-black body, while yellow-black triplefins have black heads (and sometimes black tail fins) and bright-yellow bodies. Mottled twisters, too, become very dark, but the pectoral fins and first dorsal fin are scarlet. The dorsal fin of cryptic (Cryptichthys jojettae) triplefins is similarly coloured, but in addition the belly is bright canary yellow and the throat region black with white dots.
Spawning generally takes place in winter and early spring, although some species begin as early as late May. Males become increasingly territorial and defend nesting sites from other males. These sites are in protected situations such as in cracks or under boulders, although disused shells and even artificial surfaces such as sheets of metal are also used. Both common and variable triplefins often have nests on open rock surfaces, although these are usually adjacent to a wall or in a depression.
Spawning behaviour has been observed in several species and seems to be relatively uniform, but unless otherwise indicated the following description applies to common and variable triplefins.
When ready to spawn, a female moves into the territory of a male, although a male will often lead a female to his nest following a display that involves spreading the fins, quivering, and intensification of the breeding colours. Once in the nest, the female lays eggs in batches, moving aside every few seconds to allow the male to fertilise them. The eggs, 1–1.5 mm in diameter, are covered with a sticky layer or filaments that adhere to the nest surface, which the male has cleared of algae and encrusting animals. A nest may contain several hundred to several thousand eggs, laid by one or more females, and breeding takes place several times during the season.
Breeding success among male variable triplefins appears to depend mainly on body size and aspects of the territory. Females tend to prefer bigger males with territories adjacent to large boulders and offering maximum choice of nesting sites. After spawning, a female leaves the nest and plays no role in brood care.
Male triplefins guard and actively fan the eggs until they have all hatched, which in the case of variable triplefins takes seven to ten days in northern waters and about 18 days in the south. The hatchlings, 5–6 mm long, float to the surface, where they lead a planktonic existence for two or three months. They are most abundant close to shore, although some associate with floating seaweed and can drift considerable distances offshore.
Reef settlement in most species takes place between August and January, by which time the hatchlings have grown into juveniles 15–20 mm long. Observations in northern New Zealand suggest that the number of adult triplefins on reefs drops in the early part of this period, probably as a result of the stress of a second cycle of spawning and nest-guarding.
New Zealand’s reef triplefins range from the brightly coloured and highly visible to the cryptic and almost invisible. Estimates of abundance are biased in favour of the former. (Estimating the abundance of highly cryptic species entails the release of anaesthetic or poison in a confined space, so that all fishes present can be collected and counted.)
The best studied of New Zealand’s triplefins is the variable triplefin (Forsterygion varium), which, at 15 cm long, is one of the larger species. Despite its name, it normally displays a distinctive pattern of alternating light and dark blotches along the sides of the body. It is found in a wide range of reef habitats, but is most common amongst algae on large rocks to a depth of 10 m. In the shallow broken-rock habitat of Goat Island Marine Reserve, at Leigh, variable triplefins are found in densities of 3300 per hectare and defend territories of one to two square metres throughout the year. The function of territory is thought to be the protection of food resources, since when variable triplefins are removed from patches of reef, the feeding intensity of other fishes, such as spotties (Notolabrus celidotus), increases in the vacated areas.
In the early 20th century, variable triplefins were introduced to the estuary of the River Derwent, near Hobart, in Tasmania, probably along with shipments of live oysters. The population there is thriving in sheltered, silty conditions quite unlike those the species prefers in New Zealand waters.
Probably the most widespread New Zealand triplefin is the common triplefin (F. lapillum). Although this species exhibits a variety of colour patterns, from uniform black to uniform white depending on habitat and reproductive status, it usually sports a distinctive longitudinal black stripe. While often found in intertidal pools and sheltered harbours, it is also extremely abundant in the upper few metres of water on coastal reefs that are not exposed to strong wave action. They favour cobble areas in particular, although they also frequent areas of mixed algae, kelp forest and even patches of sand.
Interestingly, common triplefins haven’t been recorded from the Three Kings Islands or the Chatham Islands. In the Hauraki Gulf they have been observed cleaning parasites from other fishes, mainly parore (Girella tricuspidata). They reach 5–8 cm in length, with the largest specimens found in the south.
The yellow-black triplefin (F. flavonigrum) and the banded triplefin (F. malcolmi) are found in deeper water than the common or variable. The yellow-black, a small 6 cm species, has a very wide distribution, from the Three Kings Islands in the north to the subantarctic Auckland Islands. Non-spawning fishes are white anteriorly and yellow posteriorly, and have black eyes and a black stripe extending halfway down the body. They are most common on deep reefs amongst kelp or sponges. Banded triplefins also tend to be found in deeper reef habitats and have a distinctive pattern of chocolate-brown bands along the body.
The plankton-eating oblique-swimming triplefin (Obliquichthys maryannae) is unique amongst triplefins in its habit of schooling in the water column above reefs. The species is yellow to orange in colour with a black longitudinal stripe, and reaches 8 cm in length.
The mottled triplefin (Grahamina capito) and the robust triplefin (G. gymnota) both attain a length of about 9 cm and have a similar colour pattern. Mottled triplefins are most common in sheltered habitats, such as bays and harbours, but they are also found on sheltered reefs, especially those with sand around them. Even in exposed sites, such as are common along the south coast near Wellington, mottled triplefins can often be found in rocky channels away from heavy swell. Robust triplefins are usually found amongst encrusting invertebrates, and are often seen beside wharf piles. Their main habitat seems to be exposed rocky reefs along sandy coasts, especially those on which there are mussels to provide cover. Like the variable triplefin, the robust triplefin has been introduced to the Derwent estuary near Hobart.
The genus Notoclinops contains three small, brightly coloured species found mainly in clear water on rocky reefs where there is strong wave action. The blue-eyed triplefin (N. segmentatus) reaches a length of 6 cm and is distinguished by its iridescent blue eyes and colour pattern of red bands on a white background. It is the most abundant triplefin around northern New Zealand’s offshore islands, although it is also common on exposed reefs along the mainland coast. It is generally found amongst a cover of mixed algae or encrusting invertebrates in water less than 10 m deep.
The blue-dot triplefin (N. caerulepunctus) grows to just 5 cm in length and is the smallest species of triplefin found in mainland waters, although it is most common around offshore islands. It is typically found among encrusting invertebrates on vertical rock walls or the roofs of overhangs at depths of over 10 m. Although brightly coloured with orange splotches on the anterior body and a series of black bands separated by electric-blue dots towards the tail, it is usually hard to detect amongst the cover of sponges, ascidians and bryozoans.
Both blue-eyed and blue-dot triplefins—the latter especially—have been observed removing parasites from larger fishes, such as moray eels.
Yaldwyn’s triplefin (N. yaldwyni) also tends to be most common around offshore islands. It has a pattern of small black dots on a background that varies from pinkish to orange.
The scaly-headed triplefin (Karalepis stewarti) is a large species, reaching a length of 15 cm, and is characterised by the presence of interlocking, bony scales on the head. The colour pattern consists of irregular brown stripes on a background of pinkish-white to fawn, with an orange to red dorsal fin. Scaly-headed triplefins are usually seen resting head-down in crevices or on the roofs of overhangs, and are found in a wide variety of reef habitats from the intertidal zone down to a depth of 30 m.
The genus Ruanoho contains two species that are well described by their Maori generic name, which means “hole dweller”. Both the spectacled triplefin (R. whero) and the long-finned triplefin (R. decemdigitatus) are wary fish that do not stray far from shelter in crevices or under boulders.
Spectacled triplefins grow to 9 cm long, and are usually reddish-brown with a distinctive pattern of bright-blue lines on the head and circling the eyes. They are most common at depths of more than 5 m in habitats that provide shelter, such as cobbles, boulders and broken rock. Males defend small territories of about half a square metre.
Long-finned triplefins grow to 12 cm in length, are fawn-coloured with light and dark spots in longitudinal rows along the body, and prefer silty, coastal habitats. Juveniles, which are often seen in intertidal rock-pools, have a bright-blue spot in the first dorsal fin.
The remaining seven species of temperate rocky-reef triplefin are infrequently observed subtidally, either because they are highly cryptic or because they occupy habitats seldom visited by divers. Nevertheless, some are extremely common and thus important to the ecology of rocky reefs. The genera Cryptichthys, Bellapiscis and Blennodon form a small group of related species that inhabit shallow, surgy habitats.
The cryptic triplefin (Cryptichthys jojettae) is well named, and in my experience most divers are unable to find it until they have been shown a specimen by an experienced observer. It prefers vertical rock faces and hides amongst red turfing algae and around the bases of larger red algae such as Osmundaria and Pterocladia. It reaches a length of 6 cm and moves in short darts.
Probably the most familiar triplefins are the two Bellapiscis species found in rock-pools. The twister (B. medius) and mottled twister (B. lesleyae) were recognised as separate species only in 1987. It was intriguing how two such similar fishes could coexist in what appeared to be the same habitat. Then Andrew Stewart, from Te Papa, told me he’d noticed that B. medius seemed to frequent pools higher up the shore than B. lesleyae, raising the possibility that the ecologies of the two species might in fact differ.
Between us, at several locations, PhD students Maren Wellenreuther and Zoë Hilton and I counted all individuals of both species in rock-pools between low and high tide, and found that B. medius did indeed favour pools higher up the shore. B. lesleyae tends to prefer pools that are exposed only at very low tide, and is probably best considered as a species that occupies the upper levels of the subtidal zone. This is reflected in the ease with which the two species may be photographed: B. lesleyae can be photographed with relative ease on SCUBA at high tide, but one has to lie in pools at high tide to photograph B. medius. Zoë Hilton has found that the two species appear to be physiologically adapted to their subtly different habitats: in particular, B. medius is better at handling the high temperatures that can occur in pools well up the shore.
The giant triplefin (Blennodon dorsale) lives in one of the harshest environments encountered by coastal fishes: the upper subtidal zone of extremely exposed coastlines. Here it must endure pounding by oceanic swells and abrasion by sand and gravel. It seems to be most common on the west coast of both main islands along shores of mixed rock and sand, where it is found from intertidal pools down to a depth of 12 m. The giant triplefin grows to more than 16 cm in length.
The genus Gilloblennius contains two extremely secretive and poorly known species. In five years of observing, collecting and photographing triplefins from the Three Kings Islands to Stewart Island, I have seen only two of each underwater. The thripenny (G. tripennis) is a heavy-bodied triplefin with prominent scales, usually found in shallow water around dense patches of medium-sized seaweeds, such as Xiphophora. The obscure triplefin (G. abditus) is known from only a few locations, all extremely exposed, including the Three Kings Islands, Tapotupotu Bay, by Cape Reinga, Sugar Loaf Island, off Taranaki, and the Snares Islands.
I saw my first obscure triplefin at the Three Kings Islands in March 2002. Graham Hardy directed the search party to an isolated rock off Great Island, where we jumped ashore from an inflatable. The seaward side of the rock was a steep slope dotted with small, seaweed-filled pools totally exposed to the ocean swell. There, amongst the weed, we collected a couple of specimens. Although obscure triplefins have been collected subtidally on a couple of occasions, their wave-washed habitat and highly cryptic colouration make them an almost impossible subject for underwater photography.
The last two species of rocky-reef triplefin are arguably the most extraordinary fishes in the family. Both the topknot and the brown topknot (N. compressus) live among seaweed and are so highly modified to suit that they look quite unlike triplefins. The topknot is the largest species of triplefin in the world, growing to 25 cm long. It is found down to about 15 m amongst kelp or other large seaweeds, amongst which it is extremely hard to detect. Topknots move by “walking” on their paired fins, although they are capable of bursts of speed if disturbed. Mottled green to brown, they blend with their habitat, and their dorsal, anal and caudal fins have transparent “windows” that break up the outline of the body.
The brown topknot reaches a maximum length of 9 cm, and can be distinguished from its larger relative by its shorter jaw and the relative length of two of the three spines in the first dorsal fin: the topknot has the longest first spine, the brown topknot the longest second spine. Brown topknots are always found amongst kelp, particularly feathery species such as Cystophora torulosa and Carpophyllum plumosum. The fish hang head-down against the stipes, and are so well camouflaged that if you take your eye off them you usually have to start searching again. In shallow water in Goat Island Marine Reserve, about a quarter of the Carpophyllum plants conceal a brown topknot. A specimen can be collected by placing a plastic or mesh bag over a kelp plant, gently breaking the plant off at the holdfast and then shaking it inside the bag.
Although only a handful of species have been studied in any detail, triplefins must play an important role in the ecology of New Zealand rocky reefs given their great abundance. As juveniles and adults they are the dominant consumers of small invertebrates on reefs, and in turn provide food for predatory species such as eels, John Dory, scorpion fish, sea-perch, goat-fish and blue cod. Other fish groups, notably blennies and weed fishes, play this leading role on rocky reefs in other parts of the world.
Just why so many triplefin species are found in New Zealand waters remains unclear, although one contributing factor in their unique evolutionary radiation may be the relative lack of other small fish species. The recent taxonomic resolution of the group at least opens the door to future ecological studies aimed at unravelling the complex relationships between triplefins and other reef inhabitants.