Interesting Inverts - Perfect Porcelain

Petrolisthes is a genus of crabs that is found in all the world's oceans save the Arctic and Antarctic. They are small, easy to care for, and can be beautifully colored. The ones that we all call Porcelain Crabs are generally a pale gray to ivory, often with brilliant pink or red spots and short lines all over their large claws and backs. They are occasionally tinged light blue around the edge of their shells and legs. Interestingly, they are closely related to squat lobsters and hermit crabs and not considered “true” crabs.

In the wild, these crabs are usually found on shallow tropical reefs, rocky shorelines and tide pools, in and around corals, anemones, sponges and algae beds. All of these make for beautiful display in the home aquarium as well. The crabs don't need a ton of space, and you could keep one in a tank as small as 10 gallons. You could keep several together, as long as they all have a place to claim as a home. They don't need a sponge, or anemones or something like that specifically, just somewhere to hide, preferably where you can still get a glimpse of them. They'll be active all day, but more likely to be out and about between dusk and dawn. They'll like plenty of rock work and a good amount of flow. Porcelain crabs don't need substrate, but if you keep them in a tank with a fine-grained sand, you may get to watch them filter it for food occasionally.

Looking at these crabs, and their disproportionately large claws, you'd think they were super aggressive and looking to chomp down on anything that came their way. In truth, they'll defend their homes but are usually pretty mild mannered. In fact, they don't even use those claws that much except as a decoy. The large claws can be dropped by the crab to distract a predator, giving the crab time to scuttle to safety and the claw will grow back.

It's the smaller appendage (called maxillipeds) behind these clobbering claws that are more important. The crabs use these to filter water and substrate for food, most of which is suspended algae, micro-inverts and detritus. In a densely populated tank, a single Porcelain Crab might not ever need feeding; with enough left-over food and fish waste, they could possibly get along. We don't recommend this. They'll do much better and molt more often when given a regular supply of food. As with any filter feeder, Nutramar's live algae products are the absolute perfect food for them. We recommend starting with CRIT, and you can dose the whole aquarium, or you can target feed them with a baster, which could also be full of the Nutramar Crit, but you could also give them Gamma Rotifers, Gamma Red Plankton, or Gamma Cyclops all this way. You can dose the whole tank with CRIT every day, especially if you have other filter feeding inverts. You won't have to target feed more than once or twice a week. These crabs will also take larger food if they get hungry and will try to steal meaty morsels if they can.

That being said, because of their filter feeding mechanisms, they're usually reef safe. As with any omnivore, you should keep an eye on yours, just in case they develop an unsavory appetite for something you'd rather they didn't eat. They won't bother any fish, and most fish will ignore them unless you're keeping things like Pufferfish or Triggers, in which case, crabs were not a good choice to start with, except as food. You can keep them with other invertebrates as well, Sea Stars, bigger Decorative Shrimp, Snails and Hermits are all usually okay unless the Porcelain is really underfed.

Over time, you'll notice your Porcelain Crabs start to look dingy. They'll get all covered in fine algae and shmutz (technical term.) This is usually a good indicator that they are about to molt. As anything with a calcium based exo-skeleton, they'll need to shed it to grow, and this requires... you guessed it, calcium. It also takes a variety of other minerals and nutrients, and if you're keeping a thriving reef tank, there is enough of everything there and you don't need to worry. Even if you aren't keeping corals, as long as you're doing regular water changes, your Porcelain Crabs won't be lacking for shell building materials. They should be kept in normal specific gravity, 1.025-1.026, with a pH between 8.0 and 8.4 and keep the temps nice and tropical. While this genus of crabs is also found in temperate seas, these specific ones are not and should be kept between 70 and 78 degrees.

Porcelain crabs are small and beautiful critters for the marine aquarium. They are peaceful and fascinating to watch as they fan the water and gargle sand for food. If you've been looking for another cool critter to add to your tank, think about a Porcelain Crab (Petrolisthes sp.) from Quality Marine today!