Aquarium Invertebrates: Housing An Octopus
I have seen a number of posts recently asking for information about keeping an octopus, and thought that would make a good subject for an article this month. I certainly understand the fascination with these incredible animals, because I feel the same way myself! I have kept and bred octopuses as pets for many years, and I am still constantly amazed by their intelligence and personality. I think that they make a wonderful pet, and if their special needs are taken into consideration, they adapt well to aquarium life and can live out their entire natural lifespan in captivity.
However, you must be aware that their “entire natural lifespan” is still quite short. For most tropical species of octopus, a lifespan of about 1-2 years is all that you can expect. Also, as I said, these animals have special needs, and they are simply not suitable for most reef aquaria. Although their water quality requirements are close to those of a reef aquarium, and they need a lot of hiding places and good water flow, a reef tank is not really the best way to provide these for an octopus. Furthermore, most octopuses are nocturnal, and even those that are active during the day prefer subdued lighting rather than the intense lighting that your average reef tank provides! Although octopuses are invertebrates, and some species are certainly found on coral reefs, these animals are not particularly suitable for a reef aquarium for a wide variety of reasons that I will try to outline below. But before I get to that, I will (as usual) try to give you a bit of background about the biology of these animals.
A bit of biology
Octopuses are members of the Phylum Mollusca, making them the distant cousins of a wide variety of more familiar reef aquarium animals including the Polyplacophorans (chitons), Gastropods (snails & slugs), and Bivalves (clams & mussels). For anyone interested in more detail on these groups, I provide a simplified introduction to some of the issues of current taxonomic classifications and basic biology of the Phylum Mollusca in my Introduction to the Molluscs article (Toonen 1998). Interested readers who wish to dig deeper into the relationships among the major types of Molluscs (or any other groups for that matter) are encouraged to get onto the Internet and check out the Tree of Life web pages. Together with the squid, cuttlefishes and nautilus, octopuses are members of the Cephalopoda (or foot- heads), and for anyone interested in more detail than will be presented in this article, I very strongly recommend that you check out some of the great information about these groups and their biology on the Cephalopod web page and the National Resource Center for Cephalopods.
I also think it is worth a quick discussion of why I use “octopuses” rather than “octopi” for the plural of octopus. I frequently see posts or hear people talking about “octopi” and it is somewhat of a pet-peeve of mine. Although many medical and scientific names tend to be Latin, for which the “i” ending is the correct plural (e.g., bronchus and bronchi), the name octopus comes from Greek roots ( okt = eight, and pous = foot), and should not be pluralized in the same way. Technically, the proper pluralization of the “-us” ending for a Greek-root word such as octopus should be the suffix “-odes”, but octopodes is generally considered a bit of a mouthful, and in both the Oxford Dictionary and among the scientific community, the most common pluralization of octopus is simply “octopuses.” Even though this could be considered equally incorrect by purists, it is certainly preferable to the Latin pluralization of a Greek root in the obviously incorrect form “octopi.” So, I’ll get off my little soap-box now, but hopefully I have convinced you not to use “octopi” in the future.
Housing an Octopus
OK, having gotten that out of the way, let’s move on to discussing what are the needs for keeping an octopus happy and healthy in captivity, and why you should not add one to your reef tank. In general, the cephalopods are highly active predators that have an unusually high metabolism for an invertebrate. That means that in practice, they usually have much more particular demands on some aspects of water quality (in particular, the oxygen content of the aquarium water - I will come back to water quality when discussing filtration below) than do most reef invertebrates. This generalization is particularly true of octopuses. In that respect, a reef tank is actually likely to provide excellent water conditions to keep one of these animals. Having said that, very few reef aquaria provide for the other requirements of keeping an octopus in captivity. For example, there are a plenty of good reasons that glass tops are not popular for reef tanks, including such issues as light penetration, gas exchange, and heat retention. However, with very few exceptions octopuses are phenomenal escape artists, and even a large octopus (some of mine have had a head the size of a large grapefruit and been nearly 3 feet in diameter when spread out) can easily make a home out of a long-neck beer bottle! For a simple rule-of-thumb to suggest to hobbyists, I generally say that if you can stick your pinky finger into a hole, your octopus will be able to crawl through it. And if you happen to keep a pigmy octopus, then there is a good chance that they will escape through any hole, even small ones. Obviously, this amazing ability to ooze through such tiny holes (despite an apparently large body size) makes it much more important that you provide a carefully designed and tightly fitting cover on your tank. Without such a tightly fitting cover to your tank, there is a very good chance that your new pet will eventually end up as jerky on the floor rather than an interactive pet in your aquarium.
This leaves you with something of a dilemma: how do you leave the water surface open to allow access for filtration and efficient gas exchange while simultaneously making an escape-proof tank to prevent your octopus from climbing out (or removing the top to let itself out) and ending up on the floor? Yes, you read that right - there are numerous reports of octopuses not only being smart enough to figure out how to open the lid on their tank, but strong enough to actually do just that! Even more than simply being smart enough to escape the tank, there are even reports of octopus making “shopping trips” by crawling out of their own tank into nearby tanks to feed, and then returning to their own tank once they have captured something tasty to eat. The repeated disappearance of crabs or fish from nearby tanks has sometimes turned out to be “late night snacks” for a hungry octopus that is able to figure out that there is food a short distance away – the clever octopus figures out how to escape it’s tank, capture a quick snack, and then return home to enjoy it’s meal. Sadly, not all animals seem sufficiently motivated or intelligent enough to return to their aquarium, and many octopuses in the hobby trade have met an untimely end by drying out on the hobby room floor. Obviously, an open-topped reef aquarium is probably not going to do the trick when it comes to providing a safe home for keeping an octopus in captivity.
So, if you’re still with me, and still determined to keep an octopus, how do you go about setting up a tank for one of these amazing animals? Well, many people have come up with different strategies for preventing these extremely clever escape-artists from taking a walk across the kitchen floor. For example, some people use open tanks that are very deep, but only fill the tank part of the way such that it is a long way for the animal to climb before it can get over the top of the aquarium. This may work well for public aquaria in which a couple of feet (or more, depending on the size of the animal) of empty aquarium is easily hidden behind a wall and only the lower water- containing portion of the aquarium is open to viewing, but is probably not overly practical for most aquarists at home. Another strategy is to have less space left open at the top of the aquarium (say about 12" or so, again depending on the size of the octopus), but line the upper portion of the aquarium with Astro-Turf, which tends to discourage most octopuses from climbing across it. However, I have seen some particularly determined octopuses manage to climb across an Astro-Turf barrier, so this technique is not always effective. Furthermore, aside from the fact that there is no guarantee that this technique will always work, most people find a tank with ~12" of Astro-Turf lined space above the water line pretty unattractive! The final common strategy, and the one that I tend to recommend to most people for a home aquarium, is to use a well-sealed tank (with the top held firmly in place using bungie cords, heavy weights or even duct tape) that overflows into an open sump which provides a simple way around the problems a sealed tank presents for gas exchange, protein-skimming and filtration.
Filtration And Appropriate Water Quality
Now we can come back to the issues of filtration and water quality. Most aquarium books that mention octopus at all claim that these animals are extremely sensitive to water quality and cannot survive without reef-quality water conditions (e.g., Haywood and Wells 1989). In fact, I have said more- or-less that same thing in this very article (above). However, that statement is not entirely true. For example, Hanlon, Forsythe and colleagues have done numerous experiments with culturing octopuses in captivity and shown that these animals are pretty tolerant of a variety of water conditions that would generally be considered unacceptable for a coral reef tank (e.g., Hanlon and Forsythe 1985; DeRusha et al. 1989). In fact, in the five species cultured by these researchers to date, there was no significant decrease in the rate of feeding or growth of octopuses cultured at a pH as low as 7.5, salinities in the range of 32-38 ppt (roughly a specific gravity of 1.022 - 1.028 at 80EF), and even ammonia and nitrite concentrations as high as 0.2 ppm! In the case of nitrate, even concentrations as high as 500 ppm did not seem to affect growth or feeding significantly (although reproduction was decreased at nitrate concentrations higher than about 100 ppm). So, despite their extremely sensitive reputation, octopuses seem surprisingly tolerant of a relatively wide range of water conditions in captivity (e.g., Hanlon and Forsythe 1985; DeRusha et al. 1989). Regardless of the parameter we choose to examine, these are certainly not the water parameter values that we expect to see when discussing “excellent water quality.”
So where does this idea that octopuses require extremely high quality water come from? Well, there are two primary requirements that are similar between the water parameters needed by both coral reef aquaria and by octopuses. First, elevated concentrations of heavy metals, especially copper, are especially deadly to invertebrates, whether they are corals or octopuses. And second, reef habitats typically have highly oxygenated water, and octopuses are extremely sensitive to low concentrations of dissolved oxygen. Experiments with the common octopus, Octopus vulgaris, have shown that these animals will die when the concentration of dissolved oxygen drops to 2.5 mg/L, and are more likely to succumb to disease or injury with oxygen concentrations below about 5 mg/ L (Nesis 1982). I know that number will mean very little to most people, so I will take the time to include a little aside here about oxygen concentrations in seawater.
But first, I need to finish this section and include a little about the unusual filtration needs of n octopus. Octopuses are almost continually shedding the skin on their suckers and arms, and so there tends to be a lot of large bits floating around that need to be removed from the tank before they begin to rot. In addition to taking only large prey items, they tend to be somewhat messy eaters, and water quality can be an issue if you do not have adequate filtration in place to keep up with the production of waste generated by an octopus. The shedding of skin is one of the primary reasons that I like to use a mechanical power filter of some sort on an octopus tank – most such filters on the market today will do a good job of removing and collecting all the floating skin from the tank quite quickly. However, this also means that regular maintenance is required to prevent these filters from clogging up. Obviously, if the filter is removing a lot of shed skin from the tank on a continuous basis, that will quickly clog up the pores of any mechanical filter, and need to be cleaned accordingly. A seriously clogged powerfilter can be more harm than good to an octopus, and you must keep on top of the filter cleaning on a regular basis. Depending on the size of the tank, and the size of your octopus, this could be as often as a couple of times a week in some cases. Whatever the size of your tank and your pet octopus, it is always better to err on the side of caution and clean your mechanical filter more often rather than not frequently enough…
An Aside About Oxygen Concentrations In Seawater
The amount of oxygen which can dissolve in salt water depends on the exact salinity and temperature of your aquarium -- the table below gives you the values of oxygen saturation (mg/l) across a wide range of temperatures and salinities. Saturation is the point at which no more oxygen can dissolve in the water under normal conditions. There are conditions under which excess oxygen can be forced to dissolve into the water (such as when water is under pressure in a pump, for example), however, and under such circumstances, the water can become supersaturated with oxygen. Ignoring the variability across temperatures and salinities not seen naturally on coral reefs, the basic answer is that saturation for an average marine aquarium is roughly 6.5 mg/l. However, this value means relatively little to the overall health of your animals (which I will explain in detail below) because you may have far less or far more oxygen in the water depending on the specific conditions in your aquarium.
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Having said that, it makes sense to ask whether our tanks need to be at saturation, and what normal levels of oxygen are in the ocean in areas around coral reefs. I probably don’t have to work very hard to convince you that surf zones regularly pounded with waves aerate the water, and are probably always nearly saturated with oxygen. But what about the areas around coral reefs – how much oxygen is usually found in that water?
Well, a number of studies have shown that seawater in areas around natural coral reefs are generally between 95-110% saturated with oxygen (i.e., 110% saturated means 10% more oxygen in the water than the value given in the table above). On average, natural coral reef areas are very close to 100% saturation (e.g., Kuhl et al. 1995; Kraines et al. 1996; Leclercq et al. 1999). Obviously oxygen is important to our animals, and if water around natural reefs is usually saturated with oxygen, then we should probably strive to maintain oxygen levels close to saturation in our aquaria as well (e.g., Ng et al. 1992; Toonen 2000).
However, there is plenty of variability in the system. For example, measurements around one Caribbean island showed that night time oxygen levels range from about 5.0-6.5 mg oxygen/l, and daytime levels rise to around 7.5-9.0 mg oxygen/l (saturation was roughly 6.25mg/l) depending on the reef me asured (Adey and Loveland 1998). Daytime oxygen concentration rise above saturation because photosynthesis produces oxygen at a higher rate than it can leave the water by diffusion. This leads to the odd situation in which the areas of lowest oxygen concentration on the reef are actually those with the most gas exchange, because in highly turbulent areas with extensive gas exchange, oxygen diffuses out of the water more rapidly and is closer to the saturation level of about 6.25mg/l. On the other hand, in areas with more limited gas exchange, there are actually higher oxygen concentrations during daylight hours because photosynthesis produces oxygen faster than it can leave, and therefore it accumulates in those areas. The opposite is true at night, though, when photosynthesis does not occur, and instead respiration uses up available oxygen (Adey and Loveland 1998). Therefore, the areas with the lowest gas exchange cannot replace the oxygen that is being used up, and the concentration falls the farthest below saturation overnight. Walter Adey reports similar levels of oxygen in his ATS-based tanks at the Smithsonian, but is also quick to point out that it is not the oxygen concentration itself that is important but rather the exchange rate of oxygen that is important to the health of the an imals (e.g., Adey and Loveland 1998; Leclercq et al. 1999).
Invertebrates use something like 0.2 – 15 μL of oxygen on average per mg of body weight per hour (Bailey et al. 1994), depending on the species and a wide range of factors including size, temperature, activity level, and so on. So, what exactly does that mean in the real world? Well, let's say you start with an average well-stocked 50G reef aquarium full of invertebrates and a few fish. The respiration of the animals in the aquarium would likely be on the order of ~ 2-3g of oxygen per hour. Even if you could supersaturate the seawater (lets say it's at 9mg oxygen/l -- the highest recorded on the natural reefs I mentioned), that still only gives you about an hour before the animals would begin to show signs of suffocation if gas exchange is limited. Of course, protein skimming, turbulent water flow (e.g., "dueling" powerheads, and especially surge devices), and photosynthesis will alter that rate of exchange, and with the normal exchange rates of roughly 4-6g of oxygen per square meter of surface area per hour (e.g., Leclercq et al. 1999), the respiratory needs of your animals should be easily met. While it is true that both salinity and temperature will affect the particular value of the oxygen saturation coefficient in seawater (as outlined above) the actual maximum value of how much oxygen can dissolve in your tank is pretty much a non-factor during normal operation.
So, the bottom line is whether oxygen can get back into your tank fast enough to prevent it from being used up by the animals in your tank. In the simplest terms, without sufficient turn-over and current to allow efficient gas exchange, the rate of oxygen replacement into your tank water is not able to keep up with the rate at which is being removed by the animals and bacteria in the tank and filter. Sadly, many people do not realize that oxygen concentration is low in their aquarium until it is too late for the octopus. That extreme sensitivity to low oxygen concentration is the main reason that I recommend high turn-over skimmers for any octopus tank – although the skimmer tends to maintain better water quality, and is therefore likely to be healthier for your animal, the highly efficient gas exchange that takes place in the skimmer and maintains a flow of highly oxygenated water into the tank is well worth the cost of a skimmer on any octopus aquarium. The water coming out of an efficient protein skimmer usually contains something close to ~6 mg/L of oxygen in an average reef aquarium (depending on the exact temperature and salinity of the water – as I explained above). As long as the rate of oxygen use in the aquarium does not exceed that of replacement via skimming and turbulent mixing in the aquarium, your octopus should be fine. As soon as that well-oxygenated water enters the aquarium, however, your animals and even the bacteria in your tank and filter begin to use the oxygen within it, and the more animals and bacteria there are in the tank, the faster that oxygen is used up. So, the smaller the tank, and the larger the bioload, and the lower the flow rate and surface area available for gas exchange, the bigger problem that low oxygen is likely to be in your aquarium.
Keeping Your Octopus In Its Tank
As I mentioned above, I generally prefer to use a well-sealed aquarium with an open sump in which to keep the skimmer and filtration, but a carefully sealed tank without a sump can work just as well, provided you have a reasonably large tank (say at least 30 gallons for an octopus whose head is about the size of a mandarin orange) and good filtration. The primary problem with a sealed tank is that it limits gas exchange with the air outside the tank, and can result in decreased oxygen availability within the aquarium. There are two general ways to deal with this. The first, and generally the best option is to have a sealed top that is octopus-proof, but not air tight. An example of this would be a top made of plastic egg crate (the light diffusion panel sold at many hardware stores) that is covered with shade cloth. In this way, you have a solid lid that prevents the octopus from escaping, but you still have an open top that allows for efficient gas exchange. The second option, if it is not possible for you to make a mesh top for some reason, is to have a solid top (either glass or plexiglass) with an external air intake for your filtration. This can be as simple as an air pump running a couple of airstones in the tank, or making sure that your air intake on your protein skimmer is plumbed in such a way that it draws from the room rather than inside your tank. By having air from the room continuously added into the aquarium, you should ensure that the oxygen demand of your tank will be met, even if the air exchange at the top of the aquarium is limited by a solid top.
My recommendation here is obviously not the only way that an octopus can be kept in captivity, but I am offering you my opinion for the way in which you are most likely to have success in keeping an octopus happy and healthy throughout it’s lifespan. For example, I have seen some people have with great success with an undergravel filter and sealed glass top on an octopus tank, as well, but most octopuses tend to discover the undergravel plate makes a great cave, and promptly pull the filter apart to crawl beneath it. This leads to dramatically decreased functionality of the filter, and an octopus that you can no longer see in your aquarium. Not exactly what most of us have in mind for a pet…
In any case, regardless of the design you decide to use, I think that using a protein skimmer and power filter with carbon are always a good idea for an octopus. In addition to the reasons listed above, an efficient skimmer and some carbon will help in the event that your pet is scared into expelling its ink within the confines of the aquarium. Inking is a normal defensive strategy in cephalopods, and although it is natural it can be a serious concern in a closed system. The ink itself is not toxic (Wood 1994), but the ink can mechanically coat the gill surfaces of the octopus, and effectively suffocate the animal if it is not immediately removed. The use of activated carbon and an efficient skimmer can help to remove the ink from an aquarium, and give you more time to discover the problem and do a water change. In fact, octopuses can control the amount of ink that they expel, and if the amount of ink expelled is small and the tank is large, use of carbon and skimming can completely eliminate the need for immediate water changes (Johnston and Forsythe 1993). Having said that, however, I always think it is a good idea to err on the side of caution, and I usually recommend an immediate water change in response to inking as a precaution regardless of carbon use. Also, it should be obvious, but after an octopus has inked, if the activated carbon is doing its job, your carbon will be fouled and needs to be replaced immediately in case your pet inks again.
Flow In An Octopus Tank
Most species of octopuses like a relatively high flow rate, but that also proves problematic for keeping these animals because most people use powerheads in an aquarium to generate flow, but I cannot really recommend that solution for an octopus tank. Octopuses have extremely sensitive arms, and they tend to be very tactile animals: like small children, they like to touch, explore, and play with everything they encounter in their environment. If the impeller of your powerhead is easily accessible (and almost all of them are), powerheads essentially function as a tentacle blender for the curious animal. The strength of these animals makes properly shielding the intake of a powerhead that much more difficult, because octopuses like to remove them. In fact, it has been my experience that the various friction-fit filter baskets typically used to diffuse the intake flow (and prevent animals from being sucked into a powerhead intake) are easily removed by an octopus, even after I had glued them in place. Personally, I prefer to have only an overflow for the open sump in my tank and a remote pump that turns over the tank volume at least 5-6 times per hour. Even with a mesh-covered overflow, my octopuses have tended to stick their arms into these intakes on a regular basis, so I am very hesitant to use a powerhead in any octopus tank.
However, having an overflow presents its own set of problems, and need careful attention to prevent disaster. First of all, the overflow must be covered in such a way that the octopus itself cannot get through the overflow and escape. As I mentioned previously, even a relatively large animal can squeeze itself through an opening the size of an average adults pinky finger, so you need to make sure that the mesh is small enough to prevent your octopus from getting into the overflow. Some people accomplish this by using a PVC standpipe and gluing a bioball into the standpipe with epoxy to prevent the octopus from removing it. Others use a plastic mesh that is held on with a cable-tie or some such thing. Whatever solution you decide upon, it is important that it 1) is small enough that it does not allow the octopus into the overflow, and 2) is large enough that it does not restrict flow. The restriction of flow tends to be more of a problem through time than when the mesh is first installed. As I mentioned above, octopus tend to shed a lot of skin flakes on a regular basis, and if these are allowed to collect on the standpipe drain, there is a good chance that drain will become clogged and your tank may overflow. This is a serious problem, and the smaller the mesh size used, the more likely clogging will occur, and the more quickly it tends to happen. Therefore, there is a trade-off between making sure that your octopus won’t escape and making sure that your overflow won’t clog: ideally, you want to use the largest mesh size that you can to ensure your octopus cannot enter the drain for this application.
Feeding Your Pet Octopus
The last problem that I will mention in detail is feeding of your pet. As I mentioned now several times, I do not consider an octopus a particularly well- suited addition to a reef tank. In addition to the reasons that I mentioned above, there is the fact that any molluscs, crustaceans and likely even fish in the average reef aquarium will eventually be eaten by an octopus. This is obviously a concern with any tankmates that you try to add to an octopus tank, but of particular concern in a reef tank, because in general, reef aquarists use a variety of herbivorous snails, hermit crabs or other small crustaceans to control nuisance algae in the aquarium, and these “clean-up” crews are often fairly expensive. The addition of an octopus to your reef tank will quickly eliminate this population of clean-up animals from your tank, because these are the same animals which are the favorite prey of an octopus in the wild. Although it would be a healthy diet for your octopus, it is also certainly an expensive way to feed your new pet. Even more expensive would be the loss of giant clams ( Tridacna spp.) that would immediately or eventually prove too tasty a treat for your octopus to resist. The eventual loss of most of the animals that typically perform as the clean-up crew in your tank, especially when coupled with the additional nutrient input from a relatively large and highly active animal such as an octopus (even a pygmy octopus produces an enormous amount of nitrogenous waste in comparison to a similarly- sized coral), makes it very likely that you’ll experience a pretty significant increase in algal growth in your reef tank.
Even if you don’t mind having an octopus eat the majority of their tank mates, there are other problems you’ll face with trying to keep an octopus in a reef aquarium. Even the cnidarians (corals, anemones, hydroids and the like), which an octopus is unlikely to try to eat turn out to be problematic, but in the other direction this time – as I mentioned above, octopuses have extremely sensitive arms, and the constant stinging by the cnidarians is both a source of stress and potential infection for your octopus. All-in-all, the vast majority of reef aquaria quite simply provide an inappropriate place to try to keep an octopus alive and healthy for extended periods of time in captivity...
So after all that, if you are still determined to get one of these animals, what can I suggest for you to provide the best care possible for your new pet? First of all, as I’ve belabored in detail above, an octopus needs its own tank, and one that will prevent it from being able to escape. Second, these animals are active marine predators and they require quite a bit of high quality food. “High quality food” does not mean feeder goldfish! Feeder goldfish have approximately 10 times as much saturated fat as any prey item in the natural diet of an octopus, and the continuous input of highly fatty foods into their diet has a dramatic effect on their expected lifespan in captivity (Toonen 2001) . Although many people are fascinated by the ability of an octopus to hunt down prey, feeder goldfish simply make a lousy food item for any marine predator (Toonen 2001) , and will contribute to an early death for your animal. So, if you can’t use feeders, what should you feed your octopus?
Well, the natural prey of octopuses consists primarily of other molluscs (especially when young, but in some species throughout their lives) and crustaceans (Boyle 1987). Obviously, you should make an effort to provide such foods, and you should also try to get the freshest (live if possible) variety of seafood prey to ensure your animals health. If fresh or live crustaceans are not easily available, the best alternative is to feed your pet good quality frozen shrimp (after you have thawed them, of course), provided that you try to vary the diet from time to time with other prey that is available (e.g., DeRusha et al. 1989). It also turns out that freshwater crustaceans have a nutritional profile surprisingly close to that of their marine cousins (Toonen 2001). So, another excellent alternative food for your octopus would be to include a variety of freshwater crustaceans in their diet as well. Live ghost shrimp are one alternative that usually prove easy to locate (many petshops now carry feeder shrimp) and are easily fed on nutritious fish food prior to feeding them to your octopus. Another potential for many people is live crayfish, which are seasonally abundant in many areas and often sold at bait shops for fishermen. Both of these live foods provide the same opportunity for your pet to hunt live food, while also providing a much more nutritious alternative to goldfish.
Enriching Your Pets Life
The reason that I encourage you to find a suitable alternative live prey to feed your octopus is simple. Aside from the nutritional issue, live prey has another benefit over fresh or frozen seafood: your octopus will have to hunt it. This may seem unimportant to you, but it turns out to be very important to your pet. As I mentioned above, these animals are extremely intelligent predators, and spending their life in a completely predictable and unchanging glass box is not only boring for them, it has a strong impact on both their health and behavior (e.g., Wood and Wood 1999). In fact, during his research with baby octopuses at Dalhousie University, James Wood discovered that he could prevent “suicides” (animals crawling out of their tanks and drying out) by adding sufficient numbers of toys and challenges to keep the animals interested (e.g., Wood and Wood 1999). Professional zookeepers have long recognized that captive animals housed in unnatural and unstimulating enclosures can develop abnormal, repetitive and neurotic behaviors, and most zoos have made a serious effort to enrich the environment in which their animals are housed to avoid such behaviors (which has led to the development of a trade journal for zookeepers and professional aquarists titled The Shape of Enrichment to exchange ideas to better stimulate captive animals). Octopuses are no exception to this issue, and a captive animal housed in a tank without sufficient hiding places and without sufficient stimulation can develop a number of stress behaviors including white color patterns, inking, frequent deimatic displays (these are sometimes called “startle flashing” in which false eye spots or brilliant colors are suddenly displayed in an attempt to startle a potential predator), autophagy (eating the tips of their own arms), hiding all the time (depending on species, however, this may be natural in some particularly timid species), and rapid jetting into the side of the tank, among others (e.g., Wood and Wood 1999). It is therefore critical that you make every effort to try to provide sufficient stimulation to your pet in order to avoid such behaviors and prolong their life in captivity.
There are many options for enriching the environment in which your animal is housed, but providing an abundance of live prey periodically is one of the simplest and most satisfying for your animal. Even in locations where live crustaceans are not easily obtained (either as bait or from a seafood shop or Asian grocery), there are usually alternatives such as “feeder glass shrimp” available from pet shops that can provide a nutritious and stimulating treat for your animal. Other options are to periodically feed your octopus in a novel way such as using a bamboo skewer through a cork to feed fresh shrimp, or placing the food item in a plastic bottle with a drilled cork sealing it. Some animals will figure out these games very quickly and become bored with them again, whereas others may never figure them out and simply give up (Wood and Wood 1999). In any case, it is important for you to continue to come up with new ideas to challenge your pet, and a variety of aquarium safe (i.e., no metal!) toys (such as a ping-pong ball or some cat toys) for your pet to amuse themselves.
Beyond enrichment being important to the physical and mental health of your pet, it will also make your octopus a much more enjoyable and interactive pet. For example, in the article I mentioned above, James Wood also found that animals that were initially very shy about feeding became much more interactive in response to such games. Within two months of starting these enrichment experiments, his octopuses went from constantly hiding to immediately coming out of their lairs and moving about on the glass while flashing “excitement” colors as soon as he entered the room (Wood and Wood 1999). Although it is impossible to know what an octopus is really thinking, this behavior has been compared to that of a dog getting excited and jumping about when you return home from work. I’m sure that anyone who is interested in keeping an octopus as a pet would much rather have the latter (excited interaction) than the former (constantly hiding) behavior in their pets. I can say from personal experience with many pet octopus over the years, that if you put in the time and effort to provide your pet with a stimulating and safe environment, they will become a highly interactive and enjoyable pet that you will remember long after their short lifespan has passed.
So, if this article has whet your appetite, and you are serious about trying to keep an octopus, I would encourage you to check out the two great resources on the web that I listed above (The Cephalopod and NRCC pages), which are absolutely fantastic sources of information about these fascinating animals! I would also encourage anyone who decides to get an octopus to set up a special tank that provides for the unusual needs of these animals, and make every effort to provide proper food and suitable toys with which the animal can entertain itself. Try to imagine that your pet is a small child, and consider what you would do to entertain a small child that was not allowed to leave their room. If you can succeed with that, you’ll likely have a happy and healthy pet that will repay the effort through their interactions with you.
- Adey WH, Loveland K (1998) Dynamic Aquaria: Building Living Ecosystems. Academic Press, San Diego, CA
- Bailey TG, Youngbluth MJ, Owen GP (1994) Chemical composition and oxygen consumption rates of the ctenophore Bolinopsis infundibulum from the Gulf of Maine. Journal of Plankton Research 16: 673-689
- Boyle PR (1987) Cephalopod Life Cycles. Academic Press, London, UK, 441 pp.
- DeRusha RH, Forsythe JW, DiMarco FT, Hanlon RT (1989) Alternative diets for maintaining and rearing cephalopods in captivity. Laboratory Animal Science.
- Hanlon RT, Forsythe JW (1985) Advances in the laboratory culture of octopuses for biomedical research. Laboratory Animal Science.
- Haywood M, Wells S (1989) The Manual of Marine Invertebrates. Tetra Press, Morris Plains, NJ.
- Johnston L, Forsythe J (1993) An Octopus in Your House? - Part II. Aquarium Fish Magazine 5
- Kraines S, Suzuki Y, Yamada K, Komiyama H (1996) Separating biological and physical changes in dissolved oxygen concentration in a coral reef. Limnology and Oceanography 41: 1790-1799
- Kuhl M, Cohen Y, Dalsgaard T, Jorgensen BB, Revsbech NP (1995) Microenvironment and photosynthesis of zooxanthellae in scleractinian corals studied with microsensors for O2, pH and light. Marine Ecology Progress Series 117: 159-172
- Leclercq N, Gattuso JP, Jaubert J (1999) Measurement of oxygen metabolism in open-top aquatic mesocosms: application to a coral reef community. Marine Ecology-Progress Series 177: 299-304
- Nesis KN (1982) Cephalopods of the world. T.F.H. Publications, Neptune City, NJ
- Ng WJ, Kho K, Ho LM, Ong SL, Sim TS, Tay SH, Goh CC, Cheong L (1992) Water- quality within a recirculating system for tropical ornamental fish culture. Aquaculture 103: 123-134
- Toonen R (1998) Reefkeeper's Guide to Invertebrate Zoology, Part 13: Introduction to the Molluscs
- Toonen R (2000) Invert Insights: Dissolved oxygen in the reef aquarium. Tropical Fish Hobbyist #531: 86-90
- Toonen R (2001) Invert Insights: Why feeder goldfish make lousy food for marine predators. Tropical Fish Hobbyist #547: 94-99
- Wood JB (1994) Don't fear the raptor: an octopus in the home aquarium. Freshwater and Marine Aquarium (FAMA) 17: 128-144
- Wood JB, Wood DA (1999) Enrichment for an advanced invertebrate. The Shape of Enrichment 8: 1-5