Emerald crab reef compatibility check
Mithraculus sculptus
Emerald crab (Mithraculus sculptus) is a beginner-level crab that needs at least 20 gallons. It is reef safe with caution; can become opportunistic with corals or small animals. Temperament varies and adults reach about 2.5 inches. ReefCrafter schedules it as middle-stage livestock, with no tank-age gate beyond a finished cycle.
Algae-eating crab that should be added for a specific job, not as a default package item.
Who it is for
Good fit for
- ✓ Tanks of 20+ gallons at the animal's adult size.
- ✓ Beginners following a slow, planned stocking order.
- ✓ Newly cycled tanks with a compatible stocking list.
Not a fit for
- ✕ Tanks under 20 gallons, even while it is small.
- ✕ Reefs where the cautions on this page would put existing corals or inverts at risk.
- ✕ Can become opportunistic with corals or small animals.
Compatibility warnings
- Can become opportunistic with corals or small animals.
- Check adult size against the final tank, not the fish or coral at purchase size.
- Add livestock slowly so the bioload and nutrient export can keep up.
- Use the planner when this animal changes the tank-size, flow, lighting, or stocking plan.
Professional planning context
- Use the 20 gallon minimum as an adult-planning floor; display length, aquascape, and existing tankmates can raise that floor.
- This can be planned early after cycling, but only after quarantine/acclimation logistics and stocking order are settled.
- Invert plans should account for copper exposure, acclimation sensitivity, predation risk, and whether the tank can actually feed the animal.
Tank fit and maturity gate
ReefCrafter uses 20 gallons as the planning floor for adult size, swimming room, nutrient load, and aggression margin.
This species can be planned early when the tank is cycled and the rest of the stocking list is compatible.
Care notes
- Temperament
- Varied
- Reef safety
- Caution
- Adult size
- 2.5 in
- Placement
- Build dependent
- Diet
- Build dependent
- Flow
- Varied
- Light
- None
- Bioload
- 0.2
- Stocking stage
- Middle
Related species
- Coral banded shrimp
Same 20-gallon floor.
- Fire shrimp
Same 20-gallon floor, reef safe.
- Scarlet skunk cleaner shrimp
Same 20-gallon floor, reef safe.
- Skunk cleaner shrimp
Same 20-gallon floor, reef safe.
Equipment that fits
- Innovative Marine NUVO Fusion 20 Gallon AIO Long Aquarium
20-gallon display, above this animal's 20-gallon floor.
- Red Sea MAX NANO G2 Cube Reef System (20 Gal)
20-gallon display, above this animal's 20-gallon floor.
- Waterbox Cube 20 Nano AIO Aquarium
20-gallon display, above this animal's 20-gallon floor.
Related reading
Questions
What size tank does the emerald crab need?
ReefCrafter plans for at least 20 gallons, based on an adult size of about 2.5 inches, plus room to forage and the stability a larger water volume gives. Use the adult size, not the size at purchase.
Is the emerald crab reef safe?
It is reef safe with caution in ReefCrafter's catalog. Watch for: Can become opportunistic with corals or small animals.
Is the emerald crab good for beginners?
Yes. It is rated beginner care.
When should I add the emerald crab to my tank?
ReefCrafter treats it as middle-stage livestock, with no tank-age gate beyond a finished cycle. Add livestock slowly so nutrient export keeps up.