Starfish

Mingling with the Stars
Asteroidea and Ophiuroidea for our aquariums

By Sara Mavinkurve

What is it about starfish that enchants us so? Perhaps it’s nostalgia from family vacations spent on the beach, cautiously poking at beached echinoderms with plastic toy shovels before hurling them into the waves (as we assumed this to be an act of mercy). Perhaps it’s the celestial reference in pentaradial symmetry or the unique way they seem to effortlessly glide along surfaces on hundreds of tiny feet (extensions of their vascular system which employ hydraulic forces to achieve locomotion). There are many reasons to find oneself fascinated with starfish. My personal reason; they are fabulously bizarre and beautiful animals.

Star Fish Generally

Starfish have strange anatomy. They have two stomachs, connected to each other (the “pyloric stomach” and the “cardiac stomach”). The cardiac stomach, the one directly connected to the mouth, can be extended outside the body enabling the animal to digest its prey externally if need be. An extension of the stomach called the “pyloric cecum” extends throughout each of the arms of the starfish and brings food and nutrients throughout the animal. This reduces the need for a “true” circulatory system. Thus, starfish have no true “heart” or anything that more than merely resembles a circulatory system. Rather, they have a well structured system of tubes (most notably their tube feet) which All starfish have a central body (or “disk”) with a “madreporite“ on top and a mouth underneath. Starfish filter water through what’s called the madreporite, which feeds the vascular system. From the central body/disk extend multiple arms. The number of arms is usually five or multiples of five, but not always (also, these numbers are not necessarily consistent even within the same type or species of starfish).
Don‘t be fooled by their slow, docile appearance. Most starfish are ambitious predators. Most are carnivores, some are detrivores. This makes choosing the right type/species of starfish for your aquarium very important. There are actually some starfish, (e.g. the notorious “green death” brittle star) that will hunt, kill and consume aquarium fish!
Also important to remember is that most starfish do not do well in captivity. Most are very sensitive to sudden changes in temperature, salinity, etc. Often, when a starfish is dying, it will literally disintegrate (appear to actually fall apart). This often comes as quite a shock/horror to aquarists who have never seen it before. Sometimes the starfish will develop a hole in the center of its body (central disk). Other times, inner organs will appear to be spilling out of the animal. Of all aquarium animals, starfish appear to suffer some of the most spectacularly lurid deaths. However, it’s not quite as cruel as it looks. Starfish have no brains and thus do not feel pain. So however bad it might look, the starfish is not actually “suffering.” All the same, we should try to avoid fating any starfish to certain demise. Always make informed decisions when choosing livestock.

Good Candidates for Aquariums

Generally, the best starfish for aquariums are those which are relatively indiscriminate detrivores. This is for two reasons 1) they’ll be easy to feed, and 2) they’ll help consume leftover food and fish waste. In selecting a particular animal to take home, make sure the starfish appears whole (i.e. no holes, tears or recently broken arms). The starfish should have good colors and no dull or white spots (unless part of its natural patterns). The animals should be active with visible, moving tube feet.

Asteroidean (Astrinia Stars, Fromia sp., Gomophia sp., Nardoa sp.)

Though a bit controversial, Asterinidae sp (a genus, not to be confused with the Family Asteroidea) starfish, aka “Astrinia stars,” likely feed on detritus and bacterial slime. Some aquarists believe that some species have the potential to attack, eat or otherwise harm corals. I personally doubt this and have never seen it myself. As for accounts of these “blunt-armed starfish” crawling over corals, I do believe that some species do/will feed on coral mucus. Thus, there might be populations with the requisite ambition to climb over corals to find and consume this mucus. If this is the case, enough of them could, at least hypothetically, become a nuisance. Even so, I believe that their benefits (both functional and aesthetic) likely outweigh any potential for nuisance.
Fromia sp. (common name, Orange or Red Marble Starfish, Red Velvet Stars, Necklace Starfish, etc.) are good aquarium animals. Though they are a bit more sensitive to water conditions than are the uber-tough Astrinias, they are thought to have one of the best survival rates for starfish in captivity. Most found in the aquarium trade stay under four to five inches when full grown. Some species have more specific needs than others. For instance, Fromia Indica needs a more well established aquarium. As always, it’s important to do your research before purchasing any animal. Do not keep them with predators such as Trigger fish or larger crabs or Mantis shrimp. Several Gomophia sp. and Nardoa sp. are also good choices, especially if aquired when small.

Ophiuroidea

Brittle Stars (and Serpent Stars) belong to the Family Ophiuroidea. Some species are mostly beneficial detrivores. The mini-brittle stars are in fact some of my personal favorites. They are great fun to watch, especially at night or whenever they come out to feed. However, larger species can get quite aggressive, stealing food from corals and even fish. “Green Death” is the common name for a type of brittle star that can (and does) catch and eat live fish.

Some of the good guys.

Starfish to Avoid

Unfortunately, some of the worst starfish choices for aquariums are also some of the most commonly seen in stores. Members of the Protoreastor genera (e.g, Chocolate Chip Starfish, Horned Sea Star) should be avoided. These starfish often starve for lack of appropriate foods for them in aquariums. If they must be had, choose the smallest specimens available and only keep in large, less fed and well established aquariums.
The Linckia sp. include some starfish which can be good aquarium animals and some which are almost assuredly doomed from the moment they are collected. Unfortunately, not all the animals being called “Linckia Stars” are actually from the Linckia genus. The entire group of starfish called “Linckia Stars” by hobbyists, might come from several different genera, and could make up many different species. Again, being careful to distinguish common names from actual classification is important for understanding and identifying the animal. What are often called “Blue Linckia” stars (though they can come in different colors) are usually too “beat up,” in too poor condition, by the time they get to the LFS to have much hope of survival in our home systems. If you find a healthy one, in exceptionally good shape, in the right system it might have a chance. Likely though, it’s best not to even try to keep them (except perhaps to feed to your harlequin shrimp-- oops, did I say that? No!)
As mentioned previously, the “Green Death” serpent/brittle star should also be avoided (especially if you have smaller, slower moving fish). Sand sifting stars, Astropecten polyanthus, should also be avoided. They are rapacious predators of sand bed fauna. Once they eat their fill of your invaluable benthic life, they will inevitably starve to death. Lastly, avoid the chubby and/or dome shaped starfish (ex. “Doughboy Sea Star,” Choriaster and Culcita sp.) For whatever reason, they simply don’t often survive in aquariums.

Bad news: A "green death" brittle star and sand sifter starfish.

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