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Of all the marine invertebrates that can be kept in aquaria, an octopus is definitely one of the most interesting. They're weird looking, are especially intelligent, and have entertaining personalities. They can quickly change color to match their surroundings, and can even change the texture of their skin, too. So, it's easy to see why an octopus could make a great addition to an aquarium. However, caring for an octopus is quite different than caring for a fish. They can certainly be kept successfully, but they do have special care requirements and there's a lot that you need to know before trying one. With this in mind, I'll give you some basic info on octopus biology, and a good idea of what you'll need to do, and what you can expect.
Octopuses are molluscs, meaning they're cousins are clams and snails. They certainly dont look or act like clams or snails, but sometime long ago all of these organisms evolved from a common ancestor. More specifically, octopuses are cephalopod molluscs, whose sets of arms/tentacles are actually the evolutionary products of their ancestors' crawling feet. This group of molluscs also includes the cuttlefishes, nautiluses, and squids, by the way.
There at eight of these arms (you probably already
knew that), each of which is little more than a very strong and
elongated set of muscles. They are also exceptionally sensitive and
dexterous, and octopuses can perform surprising feats of both strength
and delicacy. Of course the hundreds of suckers than line the
undersides of the arms helps, as these can really get a grip on just
about anything .
Most cephalopods can also produce a dark ink-like liquid called sepia, which can be squirted out if they feel threatened. This produces a distractive cloud in the water, giving the squirter a chance to shoot off and live another day. Sounds neat, but unfortunately it can be problem in a closed aquarium. Ill come back to that later, though.
Cephalopods also have a surprisingly high
metabolism, and can eat a lot for their size. All of them are
carnivores, too, and even though the nautilus is a scavenger to some
degree, the rest are certainly predators. To be specific, octopuses
will eat fishes if given the opportunity, but their diet is primarily
comprised of various crustaceans like crabs, lobsters, and shrimps.
Unfortunately, they'll also eat snails and clams, as well, including
giant clams (Tridacnids). Note that their relatively high metabolic
rate also means they have a relatively high demand for oxygen compared
to many other marine creatures.
And lastly, I have some particularly bad news. With the exception of the nautiluses, cephalopods as a whole don't live very long. It's a real shame, but the fact of the matter is that the natural lifespan of most any of the cephalopods you'd ever be able to buy ranges from about six months to two years. A few tropical species may make it as long as three years, and some cold-water species may make it six or so, but that's about it for the vast majority of octopuses. So, you need to keep in mind that even if you do everything perfectly with respect to care requirements, an octopus still wont be around too long compared to fishes and such.
With the biology stuff out of the way, let's
look at the general care requirements that you'll need to think
about. Maintaining acceptable water quality, giving them room while
keeping them from getting away, feeding them properly, etc. all need to
be taken into consideration. So, in no particular order of importance,
here are the basics.
To start, you should strive to maintain exceptional
water quality. Salinity should optimally be 1.025 to 1.027 when
measured as specific gravity, the pH should optimally stay between 8.1
and 8.3, and ammonia should be undetectable, etc. Basically these
parameters should all be kept within ranges that would be acceptable
for a reef aquarium, with the exception of temperature. This is because
many octopuses need relatively cool water.
While 80Â°F, or even a little higher is fine for
most things kept in a marine aquarium, temperatures this high can
dramatically shorten the lifespan of some octopuses for two reasons.
Many species live in cooler waters (even some that are called a
tropical species) and are adapted to life in cool water. And, dissolved
oxygen concentrations are directly related to water temperature, as
cool water holds more dissolved oxygen than warm water. So, there's a
chance you'll need to buy a chiller (water refrigeration unit) to keep
your aquariums temperature in the mid to low 70s or even 60s if you
expect an octopus to live as long as it would in the wild. Of course,
this depends on the species in question, where you keep your air
conditioner set, what type of filtration you employ, etc. But, as a
general rule, anything over 75Â° is too high and you'll have to do
what it takes to keep the water cool.
Keeping the water vigorously moving at the waters
surface will also help to keep to concentration of dissolved oxygen
high, but in most cases it will be even better to use a trickle
(wet-dry) filter with a drip plate and exposed bioballs. Using a
skimmer is also a good way to help keep concentrations at satisfactory
levels. Conversely, fluidized bed filters, undergravel filters, box
filters, or trying to stick with some live rock and a powerhead or two
is less likely to get the job done.
Speaking of filtration, octopuses will constantly
poke around with their arms and have a bad habit of sometimes sticking
them where they shouldn't. So, whatever sort of filter you might use,
you'll need to make absolutely sure that an octopus cant get its body
parts sucked up into it. Powerheads are notorious for damaging the
tender tips of curious tentacles, thus you may need to attach some sort
of screening material over any sort of pump intakes, or forgo their use
Lastly, on the topic of water quality, it is especially important to make sure that the concentration of metals is low or none. Octopuses cannot tolerate copper in particular, which is often used to treat fishes with parasite problems. Copper tends to bind to any sort of carbonate sands, gravels, and rocks, only to come free later, too. So, if copper has ever been used in a tank, it will need to be stripped out and all substrates should be replaced before adding an octopus. Likewise, you should only use purified water, such as that that produced using a good reverse osmosis filter, and a quality brand of salt mix to prevent such metals from causing troubles.
Moving along, an octopus will eat pretty much anything else that you might try to keep with it. I wouldn't try any fishes, shrimps, crabs, snails, etc. you want to keep alive, as they'll likely end up being nothing more than expensive meals. Thus, an octopus will need a tank to itself. They generally don't get along with each other either, so only one per tank. Fortunately, most of the octopuses you might come across won't get very big, though. In fact, many folks (including me) have kept small species in 30 or even 20 gallon aquariums.
Next, you'll need to provide an octopus with a good supply of appropriate foods. Shrimps, fiddler crabs, shore crabs, blue crabs, hermit crabs, etc. are great, and freshwater shrimps, ghost shrimps, and crayfish are fine, too (Toonen, 2001). If you are lucky enough to live near a bait shop that has live stuff, providing these will be no problem. However, in most cases, dead foods will do too, as long as you try to get the freshest stuff you can. Fresh, unfrozen (marine) seafood from the grocery store is the best thing next to live stuff. Live marine fishes can also be used, albeit they would be pretty expensive compared to other suitable stuff, but you should never use any sort of live freshwater feeder fish, like cheap goldfish, or freshwater stuff from the grocery. These are unsuitable for any marine carnivores as they contain way too much fat (Toonen, 2001). Keep in mind that whatever you do use, providing some variety in the diet is also strongly suggested, as well.
Other than all that, as odd as it may sound, you'll also want to provide an octopus with some sort of entertainment. They apparently like to use their brain, and giving them toys to play with can actually keep them healthier. Pretty much anything you might read about successfully keeping octopuses includes enrichment as a part of their care requirements, so dont take this lightly. It doesn't take much though, as something as simple as a ping-pong ball can give them something to fiddle with (Toonen, 2003). Better still, providing them with live foods for them to hunt down lets them do what they would do at home too, and again, there are several sources for more ideas provided below. Additionally, any tank that will house an octopus should also have plenty of rocks, shells, and such for them to move around and hide in.
To finish up, the last thing I want to mention is the fact that there are some oddball octopuses out there that you need to be wary of. First, there's the blue-ring octopus, Hapalochlaena spp. This is certainly an attractive octopus, but it has a poisonous bite that can kill you, and their natural lifespan under normal conditions is less than a year. They're relatively expensive too, so you need to think hard before buying one. Then there's the mimic or Wonderpus octopus, which is especially fascinating, but is also short-lived, ships very poorly, may require an 8" deep sand bed to burrow in, and is terribly expensive. So, one last time, do your homework before buying.
References/Good sources for more information:
Calfo, A. and R. Fenner. 2003. The Natural Marine Aquarium Series: Reef Invertebrates, An Essential Guide to Selection, Care, and Compatibility. Reading Trees, Monroeville, PA. 398 pp.
CephBase: A database-driven web site on all living cephalopods. http://www.cephbase.utmb.edu/
Tonmo: The Octopus News Magazine Online. http://www.tonmo.com
Toonen, R. 2001. Invert Insights: Why feeder goldfish make lousy food for marine predators. Tropical Fish Hobbyist, 54(7).
Toonen, R. 2003. Housing an Octopus. Advanced Aquarist Online Magazine: http://www.advancedaquarist.com/issues/july2003/invert.htm
Wood, J.B. 1994. Don't fear the raptor: an
octopus in the home aquarium. Freshwater and Marine Aquarium,