LED Lighting, the New Horizon in Aquarium Lighting? by James Gasta, Related FAQs: Cephalopods, Cephalopods 2, Cephalopod Identification, Cephalopod Behavior, Cephalopod Compatibility, Cephalopod Selection, Cephalopod Feeding, Cephalopod Systems, Cephalopod Disease, Cephalopod Reproduction, Related Articles: Mollusks, The Ballet of the Wonderpus by Richard Ross, Dont Buy an Octopus Before Reading This

James W. Fatherree, M.Sc.

Wonderpus, Lembeh Strait.  JamesF photo.

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.

Biology Basics:

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.

 All of the cephalopods have a structure called a hyponome, which is a muscular tube that they can shoot water through. Cephalopods can draw water into their body chamber then, through muscular contraction, force it out through this tube giving them something of a jet-propulsion device. 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 forwards, backwards, up, down, and sideways with ease. And of course, octopuses can also move about using their arms more like legs, crawling over the bottom instead of swimming over it.

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.

Octopuses will spend a lot of their time out of sight, but on occasion they may come out and really show off.  JamesF photo.

Octopus Care:

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 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 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 75° 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. 

Amphioctopus marginatus. A medium sized species, sometimes called the coconut octopus, because it collects coconut pieces to surround its dens. BobF photo.

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 altogether. 

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. 

If there's a way for you to get them, any live crustaceans, like this fiddler crab, are great foods for octopuses. JamesF pix.

 However, they are clever as can be, and I believe someone told me that if they can fit their eyeball through a hole, they can squeeze everything else through that same hole. 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. Thus, 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 isnt a simple thing either, and can require a good bit of planning, as you'll need an essentially sealed tank that still has great filtration and a means to keep oxygen up. Fortunately, there are lots of places to get specific information of how to do it right (some of which I've provided below), so all Ill say here is do some homework if you need help figuring it out.

 While not particularly common, the ink can be a problem, too. If you happen to startle/stress an octopus beyond its tolerance, it may react by darting 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 isnt taken care of in a timely manner. It isnt that its toxic, but it can coat the squirters gills and lead to suffocation (Wood, 1994). So, performing a sizeable water change, using activated carbon, and running a skimmer is strongly suggested if an octopus does ink-up a tank.

Some can get huge, like this Giant Pacific Octopus, but those available at shops will stay much, much smaller.

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.

Providing an octopus with something to fiddle with and/or explore is an important part of husbandry. This one liked playing with/in glass jars.

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, 17.