Fish Active during the day

Common Triplefin

Forsterygion lapillum

iNaturalist Wikipedia

The Common Triplefin is the tiny, darting king of New Zealand's rock pools. With its unique three-finned silhouette and master-class camouflage, it is a fascinating subject for any coastal explorer.

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0 Habitats

Quick Identification

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Size

Maximum length of 70 mm (2.75 inches); weight is typically less than 10 grams (0.35 oz)

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Colors

Body is usually pale or translucent with 6-7 dark vertical bars or mottled patches for camouflage. Breeding males develop a striking jet-black head and darker fins.

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Key Features

Three distinct dorsal fins on the back
Blunt snout and large eyes positioned high on the head
Thick, fan-like pectoral fins used for 'propping' on rocks
Mottled brown and cream camouflage pattern

When You’ll See Them

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Activity pattern Active during the day

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Peak hours 9 AM - 4 PM, particularly during low tide

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Season Year-round

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Diet Micro-carnivore that feeds on small crustaceans (like amphipods and copepods), marine worms, and tiny gastropods found among the seaweed and rocks.

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Habitat Primarily intertidal rock pools, cobble beaches, and shallow coastal reefs with plenty of hiding spots.

public Geographic range

Where Does the Common Triplefin Live?

Native to the temperate southwestern Pacific, the Common Triplefin is an endemic species found exclusively in the waters surrounding New Zealand. Its range extends across the entire coastline of the North and South Islands, as well as Stewart Island and the Chatham Islands. This species is a hallmark of the New Zealand seashore, thriving in almost every rocky coastal environment from the high-tide mark down to depths of approximately 30 metres.

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1 Countries

150K km² Range

Least Concern Conservation

NZ New Zealand

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iNaturalist / Verified observation data

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Behavior

The Common Triplefin is a highly territorial and active bottom-dweller. Unlike many fish that swim through the water column, triplefins spend most of their time 'perched' on rocks or cobbles using their large pectoral fins. They move in short, sharp bursts, darting from one crevice to another to avoid predators or to snag passing prey. Their movements are so rapid that they can often appear to 'teleport' across a rock pool floor.

During the breeding season, which typically spans from late winter through summer, males become extremely territorial. They choose a nesting site—usually the underside of a flat stone—and perform displays to attract females. After spawning, the male takes on the role of guardian, aggressively defending the eggs from other fish and even larger invertebrates until they hatch. They are generally bold and inquisitive, often ignoring human observers if they remain still.

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Camera Tips

Capturing the Common Triplefin requires an underwater setup, such as an AI-powered action camera or a waterproof trail camera capable of close-focusing. The best location is a stable, medium-sized rock pool that remains isolated during low tide. Place your camera on the floor of the pool, weighted down with a small diving weight or tucked securely between two stones so it doesn't shift with the surge. Aim the lens toward a flat 'stage' of cobbles or a crevice in the rocks, as these are the fish's preferred perching spots.

Because these fish are small and move with lightning speed, use a high frame rate setting (at least 60fps) to avoid motion blur. If your camera allows for macro settings or has a close-focus lens, use it; the Common Triplefin is only about 7cm long, and a standard wide-angle lens may make them look like tiny specks. Positioning the camera just 10-20cm away from a likely perching rock will yield the best detail of their intricate scale patterns and dorsal fins.

To attract triplefins into the frame, you can gently stir up the sandy substrate near the camera to release small nutrients, or place a very small mesh bag containing a crushed mussel or piece of shrimp just out of the shot. They are naturally curious and will often investigate the 'scent' quickly. Since they are most active during the day when light is plentiful, try to time your recording for a sunny day when the water in the rock pools is clear and still. Avoid filming during heavy swells, as suspended sand will cloud the water and trigger false motion alerts on AI systems.

Similar Species

Species that look similar or are commonly confused with Common Triplefin.

Estuarine Triplefin

Has a more pointed snout and is more tolerant of low-salinity water in river mouths.

Variable Triplefin

Generally larger with more complex color patterns and prefers deeper reef water over intertidal pools.

Spectacled Triplefin

Recognizable by a dark horizontal line running through the eye, whereas the Common Triplefin has vertical bars.

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Frequently Asked Questions

Common Triplefins are diurnal, meaning they are most active during daylight hours. They are particularly busy during low tide when they are confined to rock pools and can be seen darting between crevices to forage.

If you have a property with a natural rock pool, you can attract them by ensuring there is a variety of cobbles and small crevices for them to hide in. Providing a natural food source by leaving seaweed to grow or occasionally crushing a local shellfish can draw them out into the open.

They are micro-carnivores that specialize in eating tiny marine life. Their diet consists mostly of small crustaceans like amphipods, as well as marine worms and very small snails found on the surface of rocks.

Yes, they are extremely common along almost any rocky New Zealand coastline, including those in urban areas like Auckland or Wellington. As long as there is a rocky substrate and relatively clean saltwater, they are likely present.

The Common Triplefin is best identified by its blunt snout and the 6-7 dark vertical bars on its side. Unlike the Estuarine Triplefin, it prefers higher salinity and is almost always found in or near rocky pools rather than pure sand.

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