Care guide, husbandry, breeding, disease, sourcing, and tankmate intelligence on Horseshoe Crab - written by the Fast Aquatics editorial team and cross-verified against vendor records on the live marketplace.
Horseshoe Crab (Limulus polyphemus) is a marine invertebrate kept by aquarists for reef-tank cleanup, biological control of pests, or aesthetic display. Demanding requirements make this species best for keepers with established mature systems and proven track records.
Where Horseshoe Crab comes from
Horseshoe Crab (Limulus polyphemus) is native to Indo-Pacific reef ecosystems, with wild populations distributed across coral reefs, sandy lagoons, and rocky tide pools. Captive specimens are typically wild-collected; some species are starting to be aquacultured but most Horseshoe Crab sold today still comes from wild reef collection. Sustainable sourcing matters - look for vendors who can verify their collection practices, and consider aquacultured alternatives when available.
Horseshoe Crab tank size and setup
Horseshoe Crab requires a minimum of 75 gallons for healthy adults. The minimum is based on the species' adult size (10 inches), territorial range, and behavior pattern. Most Horseshoe Crab sold at small juvenile size will reach full adult size within 12-24 months and the system must be sized to the adult, not the juvenile.
For a Horseshoe Crab setup: mature reef tank with stable parameters, live rock for cover, sandbed substrate (1-2"), reef-grade lighting if photosynthetic, and a fully-cycled biological filter at least 6 weeks old. Newly-cycled tanks under 6 weeks crash the parameters that Horseshoe Crab depends on.
Horseshoe Crab requires standard reef parameters held tightly stable: Temperature: 76-80°F (24-27°C) Specific gravity: 1.025 (refractometer-measured) pH: 8.1-8.4 Alkalinity: 8-9 dKH Calcium: 420-450 ppm Magnesium: 1300-1400 ppm Ammonia + nitrite: Both 0 ppm Nitrate: Under 10 ppm Copper: 0 (lethal to invertebrates)
Horseshoe Crab is sensitive to copper - never medicate the display tank with copper if Horseshoe Crab is present. Stable parameters beat perfect parameters.
What Horseshoe Crab eats
Horseshoe Crab is a detritivore. Eats uneaten food, fish waste, and biofilm. Generally finds enough food in a stocked tank without supplemental feeding. If population thins, drop in algae wafers or sinking pellets weekly. Feed Horseshoe Crab appropriately for its size + activity level. Overfeeding is the #1 cause of water-quality crashes in tanks of all sizes.
Horseshoe Crab tankmates and compatibility
Horseshoe Crab is generally peaceful and compatible with most reef community species. Avoid keeping with predatory fish that view inverts as food: large wrasses (especially halichoeres + thalassoma), triggerfish, pufferfish, and certain large angelfish. Multiple Horseshoe Crab can share a tank but compete for food.
Browse care guides for tankmate-compatibility tables for Horseshoe Crab and similar species.
Horseshoe Crab adult size and lifespan
Horseshoe Crab reaches 10 inches at adulthood with a captive lifespan of 10-20 years with proper care. Many marine inverts molt periodically; provide adequate calcium and a stable parameter regime to support healthy molts.
Can you breed Horseshoe Crab?
Horseshoe Crab breeding in captivity ranges from straightforward (some shrimp, snails) to nearly impossible (most starfish, urchins) due to pelagic larval requirements. Captive-bred specimens are increasingly available from sustainable aquaculture facilities; check with vendors before assuming wild-caught origin.
Common Horseshoe Crab diseases and problems
Horseshoe Crab is sensitive to copper, ammonia spikes, low oxygen, and rapid parameter swings. NEVER use copper medications in a tank with Horseshoe Crab. Symptoms of stress: reclusive behavior, color loss, refusal to feed, abnormal molting (incomplete or stuck molts). Most Horseshoe Crab deaths trace back to acclimation shock or parameter mismatch - drip-acclimate over 45-60 minutes when adding to a new tank.
Where to buy Horseshoe Crab online
Horseshoe Crab is sold at LFS (local fish stores), online retailers, and direct from breeders/wholesalers. Pricing varies widely by source, size, and quality:
Browse live Horseshoe Crab from vetted Fast Aquatics vendors with carrier-tracked overnight shipping (FedEx Priority + UPS Next Day), climate-aware hold logic, and a 4-hour DOA window with photo-evidence claims. Captive-bred or aquacultured specimens cost more upfront but arrive healthier and integrate faster.
Horseshoe Crab FAQ
How big does Horseshoe Crab get?
10 inches at adulthood within 12-24 months.
How long does Horseshoe Crab live?
10-20 years with proper care.
What is the minimum tank/pond size?
75 gallons, with larger systems strongly recommended.
Is Horseshoe Crab hard to keep?
Horseshoe Crab is rated expert difficulty.
What does Horseshoe Crab eat?
Horseshoe Crab is a detritivore; appropriate diet matches its natural feeding pattern.
Horseshoe Crab taxonomy and care recommendations cross-checked against the following authoritative references and our internal vendor + breeder database.