Octopus bimaculoides Care Sheet (two-spot octopus)

By Nancy King


"Ollie", about 9 months old -- Photo by Nancy King


O. bimaculoidesis a medium sized octopus, reaching a mantle size of 7 inches (17.5cm) and arms to 23 inches (58cm). Some remain smaller than this. The bimac is not usually heavily textured and has several common colors, such as grey with yellow splotches. O. bimaculoides can be recognized by the false eyespots on its mantle below its eyes. Other species have these ocelli but there is an unbroken blue chain as part of these dark eyespots on a bimac.

Conditions for Keeping a Bimac

A bimac should be kept by itself in a 50-gallon or larger species tank. The tank needs to be well cycled and mature, which can take up to three months to prepare. The tank should be covered and well sealed to prevent escape. Bimacs like a sandy substrate and caves of rock or several lengths of PVC pipe to hide in. Bimacs tolerate a wide temperature range, ideally around 65-72 degrees F. (18 – 22 degrees C) in the home aquarium. They don't need a lot of light – a 30-watt daylight spectrum lamp for 8-10 hours/day should be enough. All overflow holes and powerhead intakes should be covered with mesh or netting. A sump could be used to house all filtration and other equipment to keep them safe from the octopus as they can interfere with fittings.

The water must be RO or RO/DI water and the tank must be provided with an over-spec filter system. Most people use a wet/dry filter, powerhead, and also a good quality protein skimmer (very useful for the heavy waste of an adult octopus, and also to remove ink).

Water parameters

Salinity - 1.026, pH- 8 – 8.4, NO3 – 0, NO2- 0, NH3 - <30 ppm, Copper - 0

Octopuses are very sensitive to Copper (Cu), ammonia (NH3) and nitrite (N02), but they can tolerate small amounts of nitrates. Regular partial water changes are recommended, 10% weekly or 20% biweekly.


"Inklet", around 3 months old -- Photo by Carol Sauer


Hatchlings are fed amphipods or mysid shrimp. Some are then fed baby clams and small crabs. (The clams can be placed in a small shell or shallow bowl.) Young octos may be given ghost shrimp, which are easier for them to catch than shore shrimp but are not suitable for long-term use. When they are small, they can also eat hermit crabs. Most will accept only live food until they are several months old. Then they can be offered thawed frozen shrimp, fresh scallops, live fiddler crabs, live shore shrimp and eventually larger crabs (crabs should be smaller than the octo's mantle). Some will take pieces of fresh fish (never use goldfish) All seem to like crayfish. Never add more food than the octo can eat at one sitting as uneaten food may die or rot and pollute the tank. Bimacs three months old or less should be fed more than once a day.


Bimacs are friendly octopuses and will respond to your attempts to make 'friends' with them. Using a feeding stick to offer food is one way to get their attention. Individual bimacs have different personalities and many like toys such as Lego blocks. They may bite you out of curiosity, and the bite is somewhat like a bee sting (provided you are not allergic to the venom).

Lifespan and Reproduction

O. bimaculoides has a natural lifespan of 1 to 1 ½ years. The approach of the end is signaled by egg laying in the female or senility in the male.

In the ocean, the female encounters a male who gives her a packet of sperm, which she keeps until she is ready to lay eggs. Egg laying takes place toward the end of her life. The first sign of egg laying is that the female bimac builds a very secure den by piling up rocks and shells and she usually does not leave it until the eggs hatch. Even when a female has never mated, she can still lay infertile eggs, which may come as a surprise to the bimac's owner.

There are a number of instances of female bimacs continuing to eat while holed up in the den with their eggs, so food should be offered. The eggs will hatch within about two months, depending on water temperature. Although the female may die shortly after the eggs hatch, on occasion she may live on for many weeks afterwards.

Nancy King

For more information, look at our other Cephalopod Care Articles or come to the Cephalopod Care Forums to ask questions.
Original publish date
Mar 1, 2003
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About the Author
Nancy has an interest in all things cephy but especially octopus behavior. She maintains two saltwater aquariums and has kept O. bimaculoides and O. briareus as well as many other invertebrates. She joined the TONMO.com staff in March 2002 with a background in management, editing and technical writing in technology companies. She enjoys helping people with ceph keeping, including writing articles. Nancy also has a strong background in art and currently works in precious metals and watercolor with a goal of producing high quality art with marine themes. She holds an M.A. from the University of Wisconsin and presently lives in Dallas, Texas - only five hours from the Gulf!

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I've kept 3 bimacs in my life, and each one lived to within a couple weeks either side of the 2 year mark. I knew a lot about cephs in general and octo's in particular, but Nancy taught me so much more. She is a treasured font of knowledge whose work should be required reading for everyone considering cephs as pets.
I no longer keep octopuses primarily because I've become adept at creating relationships with them and growing extremely fond of them. Their life spans are just so short that from almost the very day I acquire one I begin to dread the loss.
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I can control my tank temp easily between 67 degrees-75degrees Fahrenheit depending on what species I’m keeping. It’s a 55gal pLus 15gal sump with a reef octopus skimmer, enclosed return and overflow and completely sealed tank top cut to size, octopus proof with locks! 😂 and I’ve had at least half a dozen octopuses, have tried but never managed to get hurt nor escape this tank!
It holds steady at salinity 1.025-1.026
Nitrites always show 0
Nitrates fluctuate between the 0-2 and the 2-5 usually, sometimes spikes up to the 5-10 if the octo has had a big messy meal toward the end of the week right before the partial water changes on Saturday.
Temp like I said, I can easily keep it anywhere from 67-75 degrees
PH stays within 8.19-8.34
Ammonia alert sensor always reads 0.
Large amount of live rock and 1-2in coarse carribesea substrate along with a bunch of coral skeletons coralline
Species only tank for octo. I have all of this already in the tank talk thread, but I’m on my cell phone and am too lazy to go find the link from mobile. There are crabs and snails and 2 feeder shrimp in there for some “welcome to your new home” snacks lol
What do you think, @Tomh ?
I hadn’t really considered a Bimac before, but if they are willing to make friends with their caregivers as @Nancy writes above, then that makes me very excited! It seems like if I read some more about them I shouldn’t have an issue transitioning from keeping O. Minor to the bimac.. thoughts anyone?


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I think you’d like keeping a bimac. But I think any octopus would prefer having your live rock spread out a bit mare to make accessible caves.

Hi Nancy. I just had a few questions. I haven't begun salt tank keep just yet. I've mastered my 40gal rech eco tank and the husbandry that comes with it and feel confident moving into salt tank keeping and as a long term goal be skilled enough for an bimac octo. I'm also really trying to reef keep. I've done quite a bit of digging and can't seem to find solid answers. I have a 150 gal long tank I'm going to be using for this endeavor. What flow do I need for our octo? I read that I can do soft corals and can have some starfish and spineless urchins do you think that it's ok in your experience if I had soft corals matching flow and light requirements? If not is there better suggestions how to simulate its environments. Praying you see this, thank you so much for your time

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