TankBud

Fire urchin

Asthenosoma varium

Also known as Variable fire urchin, Rainbow urchin, Leather urchin

SaltwaterInvertebrate

Fire urchin (Asthenosoma varium)
Candace Pratt · CC BY-SA 3.0

Care at a glance

Temperature
72–81°F
22–27°C
pH
8.1–8.4
Adult size
9.8 in
25 cm
Minimum tank
201 gal
760 L
Temperament
Peaceful
Social behavior
Solitary
Tankmates
With caution
Swim level
Bottom
Diet
Omnivore
Difficulty
Difficult
Breeding
No record
Rarity
Very rare
Reef safe
Not reef safe
Family
Echinothuriidae
Origin
Indo-Pacific sand and rubble slopes, eastern Indian Ocean to Japan and New Caledonia

Overview

The fire urchin is a large, venomous leather urchin for a mature fish-only or rubble tank. It is for experienced keepers only.

Did you know

The fire urchin is home to pairs of Coleman shrimp, which clear a bald patch of spines to stand in. Each pair sits between venom capsules that would floor a diver. The shrimp is one of the most photographed animals in the Indo-Pacific, and the fire urchin is why.

Caring for the fire urchin

The fire urchin needs a very large, mature fish-only or rubble tank of at least 201 gal (760 L). It grows to dinner plate size, so it needs a wide floor of fine sand and rock that is locked in place. Fine sand matters because its soft body and tube feet tear on sharp rubble.

Keep the water at 72 to 81°F (22 to 27°C) with a pH of 8.1 to 8.4, and hold nitrate low. Drip acclimate it very slowly, and never use copper. Its venom can send a careless keeper to bed for a day, so move it only with a container.

The fire urchin is an omnivore that eats algal film, sponges, tunicates, coral polyps and detritus. Feed dried seaweed, sinking pellets and bits of shellfish at night.

It is peaceful toward fish, but its taste for coral polyps and encrusting invertebrates means it is not reef safe. Keep triggers and large wrasses away from it.

Good to know

Asthenosoma varium belongs to the Echinothuriidae, the leather urchins. Their test plates overlap like roof tiles instead of fusing, so the animal is flexible and sags when lifted. It comes in red, orange, purple and white. Each short spine carries a bright blue or white capsule near the tip, filled with venom that works like a hypodermic syringe. A sting brings hours of severe pain. Besides the Coleman shrimp (Periclimenes colemani), it hosts the shrimp Allopontonia brockii and the zebra crab Zebrida adamsii among its spines.

In the wild

The fire urchin lives on sand and rubble slopes and coral bottoms across the Indo-Pacific. Its range runs from the eastern Indian Ocean to Japan, the Philippines and New Caledonia. It is found from shallow water down to about 170 m. It hides in caves by day and roams in the open at night.

Common questions

What size tank does a fire urchin need?

A fire urchin needs at least 201 gal (760 L). It spends most of its time in the bottom.

What temperature and pH does a fire urchin need?

A fire urchin is comfortable at 72–81°F (22–27°C) with a pH of 8.1–8.4.

What does a fire urchin eat?

A fire urchin eats algal film, sponges, tunicates, coral polyps and detritus. In the tank, offer dried seaweed, sinking pellets and bits of shellfish at night.

How big does a fire urchin get?

An adult fire urchin reaches about 9.8 in (25 cm).

Related species