Cephalopods are a very interesting family of mollusks. They can change color and texture in the blink of an eye, spray ink at the face of predators, and eat things three times their size. There are four living cephalopod groups - Nautilus, Squid, Cuttlefish, and Octopus. Of those four, cuttlefish and octopuses are most suited for aquarium life. Cephalopods are naturally short-lived. Their lifespans are governed by the species' maximum size and surrounding water temperature. Aquarium-friendly cephalopods will not have a lifespan over two years and you are lucky if you are able to keep a ceph for one year. Nautilus are the exception to the rule in many areas, including lifespan. They are estimated to live 15-20 years. Unfortunately, they are extremely poor candidates for captive life. Cephalopod prey items are dominated by fish and crusteceans. It is sometimes difficult to get them to eat frozen foods, so oftentimes live food must be provided in order to keep your pet alive.
Photo by UNM Biology
Below are basic care requirements for keeping cephalopods in captivity.
For octopus and cuttlefish, a canister filter along with a decent hang on back protein skimmer will give you all the filteration you need. It is wise to oversize on filteration equipment and media as cephalopods produce a huge bioload and are messy eaters. I always recommend using a sump as your filteration and can almost guarantee you that you will regret not utilizing one if you decide to go with a canister and HOB skimmer. It will definitely be more expensive to get and set up a sump than the alternative, but you will be glad you did.
Most octopuses and cuttlefish that are kept in captivity will be tropical species that do best in warm water 76-80 degrees fahrenheit. Therefore, you will most likely need a heater in your tank. Some popular species, such as the California two-spot Octopus (Octopus Bimaculoides/Bimaculatus) do better in cooler water in the low to mid sixties. In this case, a chiller is usually required to keep temperatures so low. Bimacs have been kept in room temperature water of ~74 degrees with good success, but remember that warmer water means a shorter-lived octopus.
Squid require a little bit heavier filteration and a cyllindrical aquarium. With a rectangular aquarium the squid will run into the sides and squish themselves against the glass as they swim which will damage their organs and cause them to shrotly die.
Nautilus require extreme filteration. You will need a top of the line protein skimmer, UV-sterilizer, ozone injection, and whatever else you can get your hands on to keep your water pristine. Low (usually red) lighting and a chiller should also be utilized to help mimic the envirnment in which a Nautilus lives.
Octopus care -
Octopuses can be kept in a tightly sealed, carefully planned aquarium. The most common octopuses in the trade, aside from a couple of dwarf species, require at least a 55 gallon tank. Average mantle length is 2-2.5 inches with armspans ranging from 12 to 30 inches. A small sand bed of one inch of the finest sand you can get will be enough to keep your octopus happy. You will need at least a pound per gallon of rock with various caves that your octopus can choose from to make its den. The rock will provide filteration for the huge bioload of an octopus.
Most octopuses are escape artists, and it is better for you to never find out if yours is one of them. They can fit through anything larger than the size of their beak. You will need to seal of all exits of your tank with glass tops and mesh, and then put a brick or two over the lid and duct tape the edges. This may seem extreme but it is worth it to not find your pet dried up on your kitchen floor when you get home from work.
A single fluorescent strip light with a daylight (10,000k) bulb is the ideal lighting for an octopus. Under bright light environments octopuses tend to hide more often and are more skittish. Actinic or blue lighting is not a good idea either as octopuses see blue spectrum light as very bright. For a nocturnal octopus, red lights can be used to view them without them knowing.
Tankmates for an octopus are extremely few. Some species will allow snails and hermit crabs to live peacefully with them, however usually they will eat everything they can and if they can't they will at least try to. This includes fish, eels, shrimp, crabs, pods, clams, and other cephalopods.
Photo of Cuttlefish by @ReefFrenzy
Cuttlefish care -
The most common cuttlefish in the US pet trade is the dwarf cuttlefish Sepia Bandensis. Bandensis top out at about 3-4 inches and are much less constraining than octopuses. A minimum tank size of 20 gallons for a single specimen is only the first thing that makes cuttlefish a much more realistic choice for aquarists than octopuses. You will still want about 1-1.5 pounds of live rock per gallon of water to help with filteration and to give hiding places for your cuttlefish. Fine sand for the cuttlefish to play and bury themselves in should also be given. Bandensis are a warm water species and your tank should stay above 75 degrees. You don't have to worry about a cuttlefish escaping your aquarium either, which is a huge relief and makes it so you don't have to seal your tank off.
Lighting for cuttlefish is not really an issue. You will want to avoid extreme lighting conditions such as 400 or 1000 watt metal halides, however anything 250w or equivalent and below keep cuttlefish comfortable. Because cuttlefish can handle brighter lighting, coral is now an option. You will want to stay away from any coral with long, stinging tentacles however all other coral is compatible with cuttlefish. Cuttlefish will also not bother Tridacnid clams.
Tankmates are still limited for cuttlefish. Cuttlefish are social animals that can be kept in groups with each other in larger aquariums. They do best when together from birth. Generally anything motile will be tested for taste. Cuttles will happily eat shrimp, crabs, and fish. They tend to leave snails and hermit crabs alone, allowing for a clean-up crew which is another advantage over octopuses.
One disadvantage to keeping cuttlefish over octopuses is that cuttlefish are more difficult to be able to get to eat frozen food. This means that if you cannot get yours to eat frozen you will have to buy shrimp or crabs for it regularly. Feeder fish are not recommended for any cephalopod and should only be used as a rare treat or in an emergency.
Squid care -
Aside from Bobtail Squid which have similar care requirements as cuttlefish, squid are difficult to take care of and do poorly in captivity. As I mentioned earlier in the equipment section squid require a cylindrical aquarium with little live rock. Extremely fine sand with a depth of 3+ inches will give your squid a place to bury itself. You will want to provide a few patches of live rock for the squid to hide in when they want to, but not very much.
Lighting for squids should be kept fairly dim. I would not recommend anything bright than compact fluorescents.
Keep squid alone or in groups as the only thing in the aquarium. A cleanup crew of snails and crabs and algae-eating starfish are okay as well. Squids need to be fed several times per day and will almost never accept dead food. If squids are being kept in groups and not being fed enough they will eat each other.
Photo of Nautilus by Monterey Bay Aquarium
Nautilus care -
Nautilus are best left in the ocean. They ALWAYS die in captivity. Science labs and public aquariums are the only places that have been able to keep Nautilus long term. Another reason they should not be kept is because wild populations have not been assessed so we do not know how densely populated they are. However, I will provide basic care requirements for Nautilus.
Nautilus should not be kept in an aquarium smaller than a standard 75 (48Lx18Wx20H). If they are, they will run into the sides which could damage their shell. Keep lighting to a minimum. Red lighting is best so that you can observe the Nautilus without bothering it. A small amount of live rock in the corners of the tank so the Nautilus can hide is all that should be in there. You can have more live rock in the sump.
You will need a chiller in a tank with a Nautilus in it to mimic the deep waters in which they live. It is also a good idea to set your chiller on a controller so that it gets warmer at night when they surface to feed.
No tank mates should be in with a Nautilus besides a basic cleanup crew.
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