Octopuses: Things to Know Before You Buy

Author: James W. Fatherree, MSc

They're renowned for their eight appendages and a propensity for squirting jet-black ink in a crisis, but there’s plenty more to know before keeping one of the intelligent and unusual octopuses in the home aquarium. TFH’s resident reefer explains many of the joys and challenges of keeping these fascinating creatures.

Smart, Mysterious Octopuses

An octopus is definitely one of the coolest invertebrates you could get your hands on. Not only are they weird looking and very intelligent, but they also have entertaining personalities. They can quickly change color to match their surroundings and can even alter the texture of their skin. It’s easy to see why an octopus would make a great addition to an aquarium.

Caring for an octopus is quite different than caring for a fish, however. They can certainly be kept successfully, but they do have special care requirements, and there’s a lot 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.

Grouping

Octopuses (the most accepted plural form, with second choice being “octopodes”) are mollusks, meaning their cousins are clams and snails. They certainly don’t look or act like clams or snails (past the embryonic or larval stages, anyway), but long ago, all of these organisms shared a common ancestor. Specifically, octopuses are cephalopods, a group of mollusks that also includes cuttlefishes, nautiluses, and squids.

Jet Propulsion

All of the cephalopods have a structure called a hyponome, which is a muscular tube they can use for shooting water. Cephalopods can draw water into their body chamber and force it out through this tube with muscular contractions, which grants them jet propulsion abilities. The hyponome can be pointed in different directions, and when water is vigorously expelled through it, the animal is propelled in the opposite direction. They can go forward, backward, up, down, and sideways with ease. Of course, octopuses can also use their arms as if they were legs, crawling over the bottom instead of swimming over it.

There are eight of these arms (I’m betting that you already knew that), each of which is little more than a very strong and elongated set of muscles. These are exceptionally sensitive and dexterous, and octopuses can perform surprising feats of both strength and gracefulness. The hundreds of suckers that line the undersides of the arms are of great help, as these can get a grip on just about anything.

The Blackness

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, allowing them to swim off and live another day. It’s neat, but this can obviously be a problem in a closed aquarium system, which I’ll elaborate upon later.

Ever Hungry

Cephalopods have a surprisingly high metabolism and can eat a lot for their size. They are all carnivores, and though the nautilus is a scavenger to some degree, the rest are certainly predators. More specifically, octopuses will eat fishes if given the opportunity, but their diet is primarily composed of various crustaceans like crabs, lobsters, and shrimps. Unfortunately, they’ll also eat snails and clams, including larger varieties like tridacnids (giant clams). Note that their fairly high metabolic rate also means they have a relatively high demand for oxygen compared to many other marine creatures.

Lastly, I have some particularly bad news. With the exception of the nautiluses, cephalopods generally don’t live very long. It’s a real shame, but the natural lifespan of nearly any of the cephalopods you’d 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 a year or so is the limit for most octopuses. So even if you do everything perfectly with respect to care requirements, an octopus still won’t be around too long compared to most other aquarium livestock.

Care Requirements

With the basic biology out of the way, let’s look at the general care requirements you’ll need to think about. Maintaining acceptable water quality, providing sufficient tank space, feeding them properly, etc., all need to be taken into consideration.

Water Quality

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. Basically, all of these parameters should be kept within ranges acceptable for a reef aquarium, with the exception of temperature. This is because many octopuses need relatively cool water.

Water Temperature

While a temperature of 80°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 those labeled as tropical species) and are adapted to life in cool water.

Also, dissolved oxygen concentrations are directly related to water temperature, as cool water holds more dissolved oxygen than warm water. There’s a chance you’ll need to buy a chiller to keep your aquarium’s 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 various factors such as the species in question, how you set your home’s air conditioner, and what type of filtration you employ. But as a general rule, anything over 75°F is too high, and you’ll have to do what it takes to keep the water cool.

Filtration

Keeping the water vigorously moving at the surface will also help keep the 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 bio-balls. 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.

Entanglement Hazards

Speaking of filtration, octopuses will constantly poke around with their arms and have a bad habit of sometimes sticking them where they shouldn’t go. Regardless of the filter you choose, you’ll need to make absolutely sure that the octopus can’t get its body parts sucked up into it. Powerheads are notorious for damaging the tender tips of curious tentacles, so you may need to attach some kind of screening material over any pump intakes, or forgo their use altogether.

A Metal-Free Environment

It is especially important to make sure that the concentration of metals is effectively zero. 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, rocks, and even the tank glass, only to come free later.

If copper has ever been used in a tank, it may be unsuitable, and you should never use substrates that were exposed to copper medications. Likewise, you should only use purified water, such as the kind produced using a good reverse osmosis filter, and a quality brand of salt mix to prevent such metals from causing problems.

The World on Its Plate

Again, an octopus will eat pretty much anything that may be kept with it. I wouldn’t pair it with any fishes, shrimps, crabs, snails, or anything else you want to keep alive—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 there should be one per tank. Fortunately, most of the octopuses you might come across won’t get very big. In fact, many folks (including myself) have kept small species in 30- or even 20-gallon aquariums.

Feeding

You’ll need to provide an octopus with a good supply of appropriate foods. Shrimps, fiddler crabs, shore crabs, blue crabs, and hermit crabs are great, while freshwater shrimps, ghost shrimps, and crayfish are fine, too (Toonen, 2001). If you are lucky enough to live near a bait shop with live items, providing these will be no problem, but in most cases, non-living foods will also work (for adult octopuses) as long as they’re considerably fresh. Fresh, unfrozen marine seafood from the grocery store is the next best thing.

Live Marine Fishes

Live marine fishes can also be used, but they would be pretty expensive compared to other suitable stuff, and 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 carnivore, as they contain the wrong nutrients and way too much fat (Toonen, 2001). Regardless of what you do use, providing some variety in the diet is strongly suggested.

Aquatic House Arrest

Octopuses are clever as can be. Someone once told me that if they can fit their eyeball through a hole, they can squeeze everything else through that same hole too. On top of that, they can survive out of water for quite a few minutes, which adds up to an animal that just might decide to leave its tank if you don’t take precautions to keep it contained.

So in addition to everything else mentioned above, one of the keys to keeping an octopus is figuring out how to keep it in its tank. This isn’t a simple thing, either—it can require a good bit of planning because you’ll need a tank that is essentially sealed, with great filtration and a means to keep the oxygen level up. Fortunately, there are lots of places to get specific information on how to do it right (some of which I’ve referenced below).

Exercising the Mind

This may sound odd, but you’ll also want to provide an octopus with some form of entertainment. They’re surprisingly intelligent and like to use their brains, so giving them toys to play with can actually keep them healthier.

Pretty much anything you read concerning the successful keeping of octopuses includes “enrichment” as part of their care requirements, so don’t take this lightly. It doesn’t take too much—something as simple as a ping pong ball could be provided for them to fiddle with (Toonen, 2003). Better yet, providing live foods for them to hunt down lets them perform as they would in the wild. Any tank that will house an octopus should also have plenty of rocks and shells for them to move about and hide in.

Death by Ink

It’s not particularly common, but the ink can be a problem. If you happen to startle or stress an octopus beyond its tolerance, it may react by jetting across the tank, smacking the glass at the end, and squirting out a cloud of ink. Injuring themselves on the glass is an issue in itself, but the ink alone can kill them if it isn’t taken care of in a timely manner. This isn’t because it’s toxic; it is because it can coat the squirter’s gills and lead to suffocation (Wood, 1994). Performing a sizeable water change, using activated carbon, and running a skimmer is strongly suggested if an octopus does ink up a tank.

Octopuses to Avoid

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. These are certainly attractive octopuses, but they have 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-inch deep sand bed to burrow in, and is terribly expensive. So, one last time, do your homework before buying.

References

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: www.cephbase.utmb.edu

National Resource Center for Cephalopods: www.utmb.edu/nrcc/

The Octopus News Magazine Online: www.tonmo.com

Reef Central Online Community: http://reefcentral.com/forums/forumdisplay.php?s=f0a2b1cb9c5108c00bf5c9aa92344c3b&forumid=38

Toonen, R. 2001. “Invert Insights.” Tropical Fish Hobbyist, October 2001.

Toonen, R. 2003. “Housing an Octopus.” Advanced Aquarist Online Magazine: 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, vol. 17.

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