Keeping cephalopods in captivity

Colin Dunlop November 2003 (also appears in the February/March 2004, Issue - 16 of Marine World Magazine)

“The most commonly seen cephalopods for sale in the UK are octopuses, cuttlefish and nautiluses. Their husbandry is not too far removed from caring for any other marine species but differences lie more in the misinformation and poor species identification.

As long as a few aspects are catered for, I'd argue that these are the most interesting, if short lived, marine animals we could ever maintain in the home aquarium.”

What is a Cephalopod?

The order cephalopoda consists of four main types of animals: squid, cuttlefish, nautilus and octopus, the latter having the largest number of described species (~200). The word 'cephalopod' means head-foot, which is in reference to the fact that their limbs are attached onto their heads. Cephalopods are all invertebrates and are closely related to other molluscs like slugs and snails. They are found all over the World's oceans from the shallow tropical reefs to down in the deepest sea trenches. They show incredible variety and can weigh in at only one gram for the smallest species and up to 200 kilograms for the largest member of the group the Giant Pacific Octopus.

Octopuses and cuttlefish can be cared for in captivity with relative ease, as can nautiluses if you can get a deep enough tank with a good chiller! Squid, however, are still considered impossible for the home aquarium, as they require a huge cylindrical tank that is not transparent. These pelagic animals are not suited to captivity.

The Cephalopod Aquarium

Unfortunately there are no cephalopods that are suitable for a reef tank or for a mixed community. A well maintained home aquarium would just be an expensive menu and any fish, shrimps and crabs would get eaten within a few days of adding the new inhabitant. Also bear in mind that many fish eat cephalopods and a small octopus is just as likely to disappear down the throat of a larger fish! So set the tank up as a specimen tank.

As octopuses are most commonly seen for sale the rest of this article will focus mainly on their husbandry

Tank Requirements

1. Size matters

The aquarium should be as large as possible for the species that you intend to keep. The minimum size should be at least 36x18x18 (inches) to be used for small octopus species and as big as you can get after that.

Most cephalopods lead a solitary life and cannibalism is very common so it's best to keep only one per tank.

If possible use an aquarium with a sump. This protects all your equipment and reduces the different paths of escape quite significantly. The hood of the aquarium needs to be very tightly fitted. Even species that are not prone to climbing out have been known to try.

2. Water Parameters and Quality

Cephalopods have soft bodies and are essentially naked (except the nautilus that has an external shell). They have a huge surface area and therefore are very sensitive to water quality and pollutants like ammonia and nitrite, which should all be kept at zero. Nitrates seem to be tolerated to 50 - 100ppm with no apparent ill effects.

Copper is lethal and should be tested for before the octopus is added to an aquarium. Treat them like all other invertebrates in this respect.

An octopus produces approximately three times more ammonia than a fish of a similar mass; partly due to it's having three hearts and therefore three times the oxygen requirement of fish. As a result oxygen levels should always be kept as high as possible. To do this (and to remove all the excess waste) always use oversized filters and skimmers. When an octopus feels threatened it may eject viscous ink as a smoke screen. Although it is not poisonous it can and will coat gills and this may lead to asphyxiation. The ink can often be removed by catching it in a fine net but protein skimmers and good quality carbon is a must have! Always work slowly to avoid startling a new octopus.

Salinity is the other water quality parameter that must be controlled carefully. It is of paramount importance that the octopus aquarium has full strength seawater. Aim for 1.026 at all times, a lower salinity will kill them.

PH must be kept between 8 and 8.4 and it is always worthwhile to do a 25% water change on a fortnightly basis. Remember they do produce a lot of waste!

3. Aquascaping

Perhaps the most common reason for keeping an octopus is to witness its incredible brainpower, problem-solving skills and its willingness for interaction with its owner.

Its intelligence requires an enriched environment, that is lots of things to interest it in the aquarium. The simplest way to do this is to add lots of rocks and food grade quality plastic pipes of various diameters. The rocks should be glued into position to avoid landslides through the front of the aquarium as octopuses are very strong and like to re-arrange their own 'furniture'! The plastic pipes can be littered about the bottom of the tank. A large amount of shells and various small rocks should also be added as an octopus will appreciate being able to use them to make a door on its den. Caulerpa may also be used but avoid the temptation to add corals and anemones, they may sting the octopus but more likely, the octopus's activity will bury them.

The best substrate to use is a fine, well washed silver sand. Coral sand and similar substrates are too course for an octopus's sensitive skin and may damage them as they attempt to dig.

Most octopuses are nocturnal but they will generally change their habits in the home to suit times that we are active. A great way of breaking the ice with a new octopus and building a trusting relationship is at feeding time. If food is offered on a wooden or plastic stick at the same time each day, it wont be long before the arms come out the top of the tank to take food from your fingers! Also to help encourage the shyest of individuals, keep the lighting subdued. There is no need for metal halides, a small fluorescent strip is all that's needed on a timer for approximately 10 – 12 hours per day.

Enrichment comes in many guises so be creative. One of the most interesting ways of keeping an octopus entertained is by using various toys. This includes floating table tennis balls, Lego bricks, Star Wars action figures, plastic toy sharks and possibly any item of aquarium equipment, like a thermometer or cleaning magnet, you might have left in by accident! (Insure that anything added will not poison the water! Being 'food grade quality' or 'for babies' is a good guide)

4. Feeding

In the wild an octopus's diet would consist mainly of crustaceans. This should always be reflected in the home aquarium. Although many of them will accept other food like feeder fish, this is not an ideal diet for a healthy octopus and feeder fish may have been treated with copper! An average size octopus of 18" arm span will eat approximately two 2" wide shore crabs every day or two. There are companies that supply food suitable for cephalopods.

5. Lifespan

If ever there was a drawback to keeping cephalopods; it is this: the majority have a natural lifespan of somewhere between six months and two years. Some deep sea or coldwater species like Bathypolypus arcticus have been known to live for six years. It is your decision whether or not it all seems worth it.

6. Reproduction

After becoming sexually mature, octopuses will mate and shortly afterwards the male dies. The female takes up residence in a well-enclosed den to lay her eggs. During the incubation period, which may be a month or more, the female often refuses to eat, and she will die shortly after the eggs hatch. The process of a cephalopod dying is called senescence. An unmated female will often lay infertile eggs in captivity and attempt to rear them. Unfortunately her fate is the same.

What species of Octopus are available?

What are we actually getting when we see that sucker covered arm waving at us from deep inside the live rock cavity in the dealer's tank? Buying an octopus in the UK is like the lottery. They are bought and sold with such meaningless names as 'brown octopus', 'common octopus', 'Bali Octopus' and a personal favourite 'Octopus Spp.'. This is not the fault of the shops however as octopuses are incredibly difficult to identify, even after a long time studying the group. They can change colour and body shape in the blink of an eye. One minute they may look 45cm wide and the next they've tucked themselves into a small ball. They can even lift flaps of skin on their bodies called papillae to allow them to resemble the rocks and plants surrounding them.

In all honesty there is no hard and fast octopus ID kit! Instead, here is a list of the more commonly imported species that you might find and their associated suitability. Always ask what part of the world the octopus came from as this helps to identify the species. Be warned though, you may never find out what species it is!

Octopus bocki

A small retiring species frequently sold a 'Bali Octopus'. Best described as a dwarf it is short lived and most imported specimens are fully grown adults with maybe only weeks to live.

Octopus aculeatus

This long armed species is frequently imported and has an arm span of some 30cms compared to a 4cm mantle. It has a good nature and will be diurnal once acclimatised.

Octopus vulgaris

This is the common octopus. Be aware that the above two are often confused with juveniles of this species. This octopus can reach a large size of up to a 70cm span in captivity therefore a large tank is required. Notorious for climbing out so seal the tank carefully.

Octopus briareus

This is the Caribbean or Florida Octopus. Settles in well to captive life. It normally has a reddish or bluish tinge and large eyes.

Octopus bimaculoides

The two-spot or Californian octopus is by far the best species of octopus to keep. It has a diurnal habit and doesn't get as large as vulgaris. This species is best kept at room temperature, as it is not a tropical species.

Species to avoid

Avoid the temptation of buying the following species: The Blue Ringed Octopus Hapalochlaena Spp., The Mimic Octopus and Wunderpus.

Blue rings are one of the World's most toxic marine animals with a bite that can kill a person. Frequently imported, they are poor travellers and are imported as short-lived adults. Their entire life span from hatching is naturally 6 months or so. The risks are not worth taking.

Wunderpus and Mimic octopuses do not yet have scientific names and have recently been seen in some TV documentaries. This has resulted in requests for captive specimens. Neither species is well documented in the wild and could in fact be rare. Both could potentially be toxic and the Mimic will never live up to its name in captivity refusing to act like it does in the wild. Again, normally imported as adults they are best left in the sea.

Cuttlefish and Nautiluses

There are occasions when other species of cephalopod are available. The Common European cuttlefish (Sepia officinalis) is often available but its large size (up to 18") often limits its potential for home aquariums, a 6-foot tank is minimum for one adult!

Cuttlefish are generally very poor travellers and many die during exportation from the tropics. Success rates are very low and at this point they are perhaps best avoided. Sepia bandensis is the most commonly imported species - adult at 3" long.

Nautilus is often frequently seen and is another one to be avoided unless you are planning on setting up a very deep tank and can keep the temperature in the low sixties. Anything above that will kill them in a matter of time.