Spotted robust triplefin

Where they come from

Spotted robust triplefins (Forsterygion capito) are little coastal rock-dwellers from New Zealand. You find them in tide pools and shallow reefs where the water can be surgy, bright, and full of hiding cracks. That background explains basically everything about them in a tank: they want structure, perches, and lots of micro-food drifting by.

Setting up their tank

Think "mini rocky shoreline" more than "open reef display." Triplefins spend their day hopping between perches, peeking out of holes, and doing short darting swims. If your aquascape is just a couple of big rocks with open sand, they look stressed and act skittish.

• Tank size: I would not keep one in less than 20 gallons, and I like 30+ if you want tankmates. They are small, but they use every inch of rockwork.
• Rockwork: Build a maze. Lots of small caves, overhangs, and tight crevices. They love narrow slots where only their head sticks out.
• Flow: Moderate to strong, but not a sandblaster. Aim for lots of random movement around the rock faces.
• Lighting: They do fine under normal reef lighting, but give them shaded spots so they can retreat.
• Lid: They can pop upward when spooked. A tight-fitting cover saves you heartbreak.
• Water: Keep it stable like a reef tank. Salinity around 1.025, temp in the mid-60s to low-70s F works well depending on your system. Stability matters more than chasing a magic number.

A mature tank really helps. I have had the best luck when there is already copepod and amphipod activity, plus a little film algae and microfauna on the rock. It gives them something to hunt between meals and helps them settle in.

What to feed them

They are micro-predators. In the wild they pick at tiny crustaceans and worms all day. In captivity, the biggest challenge is getting them confidently taking prepared foods, then keeping weight on without blasting your nutrients.

• Best starters: live baby brine shrimp, live copepods, or live blackworms (if you have a safe source and rinse well).
• Once they are eating: enriched frozen baby brine, finely chopped mysis, calanus, cyclops, and other small meaty frozen blends.
• Prepared foods: some will take tiny pellets eventually, but do not count on it. Frozen and live are your friends.
• Feeding style: small amounts more often beats one big dump. They are built for constant picking.

Watch the belly line. A healthy triplefin looks a bit "filled out" behind the head, not pinched. If you see them losing mass, step back and add more small feedings and more live options until they rebound.

How they behave and who they get along with

They have big personality in a small body. Most of the day they perch, pivot, and watch you. They can be territorial about a favorite hole, especially as they mature.

• Best tankmates: peaceful, non-competitive fish that do not hover in the same rock crevices. Think small gobies that stick to sand, gentle blennies (species-dependent), and calm inverts.
• Avoid: aggressive dottybacks, hawkfish, larger wrasses, and anything that sees small perchers as snacks. Also avoid fast, greedy feeders that will outcompete them at every meal.
• Inverts: generally fine with cleaner shrimp and snails. Tiny decorative shrimp may get sampled if they fit in the mouth.
• Corals: they are usually reef-safe. The main issue is them perching on fleshy corals if the rockwork forces them to.

If you want more than one, plan the rockwork like you are designing a tiny apartment complex. Multiple separate cave networks with sight breaks helps a lot. Even then, watch for one fish getting bullied off food.

Breeding tips

They can spawn in captivity, and the behavior is fun to watch. Males typically claim a little nest site (a tight cave or underside of a rock) and guard eggs. The hard part is raising the larvae, not getting eggs.

• Give them nest options: small caves, short lengths of PVC tucked under rock, and flat stones with a tight gap underneath.
• Conditioning: lots of small meaty foods and steady water. You will see more display and territory behavior when they are ready.
• If you find eggs: the male will guard and fan them. Try not to mess with the nest area.
• Larvae: plan for live plankton foods (rotifers, copepod nauplii) and a separate rearing setup if you want a real shot.

Common problems to watch for

• Not eating after introduction: very common. Keep lights lower for a day or two, offer live foods, and feed near their perch with a pipette.
• Getting outcompeted: they are not built for food stampedes. If tankmates rush food, you will need to target feed or rethink the stocking.
• Jumping: usually happens when startled or chased. Cover gaps around plumbing and lids.
• Weight loss: often from too-infrequent feeding or too-large food items. Go smaller, more frequent, and add pods if you can.
• Stress from barren rockwork: they hide nonstop, breathe fast, and stay pale. Add more structure and shaded crevices.
• Parasites and shipping damage: wild fish can arrive rough. Quarantine helps a lot, especially if they are not eating right away.