Overview
The mandarinfish is a tiny, slow-moving dragonet from the Western Pacific, one of the most spectacularly patterned animals in the sea. At dusk it threads through coral rubble picking microscopic copepods off the rock, one at a time.
That slow, live-only appetite is exactly what makes it a fish for patient experts with a mature reef full of live food, not for a new tank.
| Care level | Expert |
| Adult size | 2.5-3 in (6-8 cm) |
| Lifespan | 2-4 years |
| Temperament | Peaceful, shy |
| Min. tank | 30 gal (114 L) mature reef |
| Water | Saltwater reef |
| Temperature | 72-81°F (22-27°C) |
| Diet | Micro-predator (live copepods) |
| Home aquarium? | Yes, but expert only |
A living jewel
Its swirling maze of blue, orange and green sits over a body with no scales. Instead the mandarinfish wears a thick, bad-tasting mucus that puts off predators and parasites, so it can drift slowly in the open without much fear.
The blue that almost no other animal makes
Most blue in nature is a trick of reflected light. The mandarinfish is one of the very few animals that build a true blue pigment in their skin cells, which is part of why the colour looks so deep and glowing.
Diet, the hard part
Mandarinfish hunt tiny live copepods and amphipods all day long. Keeping one alive means a mature reef tank with plenty of live rock and a thriving copepod population, or patiently training it onto frozen and live foods.
In the aquarium
Peaceful and reef-safe, but only for an established system. Their biggest killer is slow starvation in a tank that cannot supply enough live food, which is why they are rated expert-only.
Fun facts
- Its blue is a true cellular pigment, making it one of very few animals on Earth that build blue this way.
- It has no scales; instead it wears a thick, foul-tasting mucus that fends off predators and parasites.
- At dusk, pairs rise together in a slow courtship dance before releasing their eggs into the current.
- It eats by picking microscopic copepods off live rock one by one, all day long.
- A healthy mandarinfish is one of the few reef fish calm enough to watch up close for minutes at a time.
Frequently asked questions
Why is the mandarinfish so hard to keep?
It only eats tiny live prey. Without a mature reef full of copepods, or patient training onto other foods, it slowly starves, which is why it is an expert-only fish.
Is the mandarinfish reef safe?
Yes. It is peaceful and completely reef safe, ignoring corals and other fish and spending its time hunting copepods among the rocks.
What makes its colour special?
It is one of the only animals that make a true blue pigment in their skin, rather than creating blue from reflected light like most animals do.
How big does a mandarinfish get?
Very small, only about 2.5 to 3 inches (6 to 8 cm), which is part of its charm but also means it needs tiny, frequent live foods.
