Mandarinfish

1) Where they come from

Mandarinfish (Synchiropus splendidus) are little reef dragons from the Western Pacific—think Philippines, Indonesia, and around the Great Barrier Reef. They spend their days picking tiny critters off live rock and cruising over rubble and coral heads. That “always hunting” lifestyle is basically the whole key to keeping them.

2) Setting up their tank

If you want a mandarin to do well, build the tank around food availability, not around them being “hardy.” They’re not fragile in the usual way—they just starve quietly while looking totally fine… until they don’t.

• Tank size: I’d treat 40–55g as the realistic starting point for a single mandarin, bigger is easier. You can do smaller only if you’re very deliberate with pod culture and feeding.
• Mature tank: aim for 6+ months old with established live rock, film algae, and lots of micro-life. New tanks are almost always a bad time.
• Rockwork: lots of nooks and crannies. They’re slow, methodical hunters and they need pod habitat more than they need swimming space.
• Flow: moderate with calmer pockets. They don’t love getting blasted around while they peck at the rock.
• Lid: cover the tank. They can hop, especially at night or during spats.

3) What to feed them

In the wild they eat tiny crustaceans nonstop. In a tank, that usually means copepods (and some amphipods) all day long. Some mandarins learn frozen, some never do—and you don’t want to be gambling with a fish that can waste away in plain sight.

• Best baseline diet: a self-sustaining copepod population in the display (plus refugium if you can).
• Supplement: add pods periodically, especially early on or if you’ve got other pod hunters.
• If they’ll take it: frozen baby brine, Nutramar Ova, finely chopped mysis, calanus, or quality “reef plankton” style foods.
• Feeding method that helps: a feeding dish or a small glass jar on the sand. Some mandarins learn that’s where the good stuff shows up.

4) Behavior and tankmates

Mandarins are peaceful, slow, and totally focused on hunting. They’re not “shy,” but they don’t compete well with pushy eaters. Most issues come down to food competition, not aggression.

• Good tankmates: calm community reef fish that aren’t obsessive pod hunters (many clownfish, cardinals, some gobies, blennies depending on species).
• Be careful with: wrasses (especially six-lines), scooter “blennies”/dragonets, some dottybacks, and anything that constantly picks rock for pods.
• Pairs: possible, but add with a plan. Two males will fight. A male + female can work if the tank can support them.

5) Breeding tips (fun, but a whole project)

Mandarins will sometimes spawn in home tanks, usually around dusk. You’ll see the pair rise into the water column together and release eggs and sperm at the top. It’s one of the coolest things you can witness in the hobby.

• Set the stage: stable, mature tank, well-fed pair, calm evening lighting cycle.
• Spawning cue: a dusk “dance” and an upward glide—if you see that happening regularly, you’re doing something right.
• Raising babies: that’s the hard part. The larvae are tiny and need live foods (rotifers, then copepod nauplii) on a tight schedule with very clean, very consistent water.

6) Common problems to watch for

With mandarins, the problems are usually slow and sneaky. If you catch them early, you can fix most of them. If you wait until the fish looks “thin,” you’re already behind.

• Slow starvation: the big one. Pinched belly, less interest in hunting, hanging in one area. Usually caused by low pod supply or too much competition.
• New-tank syndrome: not enough microfauna yet, even if water tests look fine.
• Overconfident tankmate choices: a single wrasse can out-compete a mandarin without ever nipping it.
• Disease: mandarins have a thick slime coat and often dodge ich better than many fish, but they’re not immune—especially if stressed or shipped poorly.
• Powerhead and overflow risks: they cruise rockwork and can get pinned or sucked into uncovered intakes.