Red Knob Sea Star

The red knob sea star is recognized by its gray body and the bright red raised knobs lined up along its arms; red lines connecting these knobs create a grid-like pattern on the body. With its arms spread it reaches 30 cm. It sells well because of its looks, but it is not a cleanup creature: it is carnivorous and eats soft corals, sponges, tube worms, clams and other sea stars. For this reason it is suited only to fish-only aquariums or to large, coral-free setups built for it. Those on the market are wild-collected.

• At least 300 liters; a large open sandy area and live rock. It forages on sandy or muddy bottoms.
• Salinity specific gravity 1.024–1.026, pH 8.1–8.4, temperature 24–27°C; nitrate and phosphate should be low and salinity stable.
• Not reef safe; it is not kept with corals, tridacna clams or tube worms.
• It should be acclimated by the drip method for at least 2 hours and never exposed to air at any stage. Copper-based medications are lethal.

Carnivorous. It cannot live on the detritus in the aquarium; chopped mussel, oyster, shrimp, squid or fish pieces should be placed under its mouth 2–3 times a week. Thinning arms and a sagging body are signs of starvation.

It moves slowly around day and night. It does not harm fish, but it eats slow and sessile invertebrates in its path.

Good companions: tangs, large clownfish, damselfish, cardinalfish and gobies.

Avoid: corals, tridacna clams, tube worms, sponges and other sea stars; pufferfish and triggerfish, which pick at it, and angelfish.