Common name: Flat Rock Crab

General Information

The Flat Rock Crab, scientifically known as Percnon planissimum, is a fascinating and agile crustacean that has captured the interest of marine aquarists. Known for its flat body and long, slender legs and quick and nimble movements. Its natural habitat spans rocky intertidal zones and coral reefs across the Indo-Pacific region, where it plays a crucial role in the ecosystem by scavenging and grazing on algae.

This species is a popular choice for hobbyists looking to add a unique and active invertebrate to their aquarium. Its striking appearance, characterized by a reddish-brown body with lighter markings and banded legs, makes it a visually appealing addition to reef tanks. However, its behavior and dietary habits require careful consideration to ensure compatibility with other tank inhabitants.

Care

The Flat Rock Crab is relatively hardy but requires a well-established aquarium with stable water parameters. It thrives in tanks with plenty of live rock, which provides hiding spots and surfaces for grazing. This species is highly active and spends much of its time exploring the tank, making it an entertaining addition for aquarists.

While generally peaceful, the Flat Rock Crab can exhibit opportunistic behavior, particularly if food is scarce. It is essential to provide a varied diet to prevent it from preying on small fish or invertebrates. Regular feeding and a well-maintained environment are key to its health and longevity.

Diet and Feeding

In the wild, Percnon planissimum primarily feeds on algae, detritus, and small invertebrates. In captivity, its diet should include a mix of algae-based foods, such as nori or spirulina, and meaty options like brine shrimp or mysis shrimp. Offering a variety of foods ensures balanced nutrition and reduces the likelihood of predatory behavior.

Feed the Flat Rock Crab once or twice daily, providing only as much food as it can consume within a few minutes. Supplementing its diet with natural algae growth on live rock can also help meet its nutritional needs.

Behavior and Compatibility

The Flat Rock Crab is an active and agile species, often seen darting across rocks and crevices. While it is generally peaceful, it may become territorial or opportunistic if food is scarce. Care should be taken when housing it with small fish, shrimp, or other vulnerable tank mates.

This species is best suited for reef tanks with larger, more robust inhabitants. It is reef-safe with caution, as it may occasionally nip at corals or small invertebrates if not adequately fed. Providing ample food and hiding spots can help mitigate these risks.

Health and Common Issues

With proper care, the Flat Rock Crab can live several years in captivity. Maintaining stable water parameters and a balanced diet is crucial for its health. Regular monitoring for signs of stress or disease, such as lethargy or discoloration, can help prevent common issues.

When introducing a Flat Rock Crab to your tank, ensure it is active and free of visible injuries. Quarantining new additions can help reduce the risk of introducing diseases or parasites to your aquarium.

Habitat

In the wild, Percnon planissimum inhabits rocky intertidal zones and coral reefs, often found clinging to rocks and crevices. Its natural range includes the Indo-Pacific region, from the Red Sea to Hawaii. This species prefers environments with plenty of hiding spots and access to algae for grazing.

In captivity, replicating its natural habitat with live rock and moderate water flow can help it feel secure and thrive. Providing a stable environment with consistent water quality is essential for its well-being.