Crabs can be helpful or not in the aquarium. Some of the larger crabs are not required as they blunder about causing damage and disruption. Others¸ such as some of the hermit crabs, are colourful, interesting and at the same time perform a useful job scavenging which assists in keeping the system clean.
Another interesting crab is the porcelain. This term is often thought to refer to one crab but this is incorrect, they are multiple. Their size is not a problem as they achieve around ¾” to 1¼”. There’s another two good reasons besides their size which makes them particularly interesting to marine aquarists. First, they are very colourful. Second, they usually reside in the tentacles of an anemone, or more unlikely down underneath it. So they are similar in that respect to clownfish.
Porcelain crabs come under various common names depending on which one it is. To take one in particular the common name is ‘dotted anemone crab’, or sometimes the general ‘porcelain crab’. The proper name is a tongue twisting Neopetrolisthes ohshimai.
They are best kept in a reef system, obviously with an anemone. Anemones such as those inhabited by clownfish are appropriate. Though one or two of this type of crab are able to defend their home against clownfish, this one is likely to lose out and it is best if the aquarist makes the choice – clownfish or crab. They are both suitable for inclusion with an anemone. It is best that one crab is kept as two of the same sex will fight.* If it is known that two are a pair then fine.
In a high quality habitat they are hardy, but it would be best for the aquarist to gain experience and feel confident about aquarium general maintenance including seawater quality before proceeding. This is not so much for the sake of the crab – experience is required for the sake of the anemone as, at least in my opinion, though I note quite a few others of experience agree, an anemone is not the ideal starter for a beginner. If an anemone and crab are to be kept, it should be remembered that the anemone requires the proper lighting, though this is likely to be present in a coral reef aquarium.
Feeding the crab is not difficult. The crab is a filter feeder and to facilitate this method the crab is able to spread hair-like fan structures into the seawater. So to feed them the aquarist could target liquidized filter type foods over them. This needn’t worry aquarists however, as the crabs will also take small pieces of de-frosted food such as lance fish, shrimp etc. The crab will not require much food though feeding should be fairly regular, and any extra food the crab ignores will probably be caught by the anemone, which in turn requires feeding with the same kind of food in larger pieces but less often.
When considering livestock for an anemone, clownfish of various types are probably the choice of most aquarists. If a crab such as that described is chosen then the interest is just as high and the sight of the two life forms co-existing just as fascinating.
(*Ref: Marine Atlas. Helmut Debelius & Hans A Baensch)