[Octopus]: This is Omikron - Abdopus aculeatus


Blue Ring
Feb 24, 2018
Vienna, Austria
Today, we were able to collect our octopus (sold as O. vulgaris from Indonesia) from the LFS. After transferring it into the tank, it immediately took the time to explore the tank in its full length, eating two (small) hermit crabs and two (small) shrimp en route. It was more crawling along the backside of the rocks than swimming, at one point creeping across the gravel snail-like. It then entered a small cave and rested for a couple of hours. When we saw it again, it appeared on the other side of the tank, sliding to and fro below a bigger live rock. At one point, it came out for a minute and stuck to the glass, so I was able to take a photo. Then something (probably me) scared it and it hid again, after a few minutes gliding again between the rocks back to the non-observable regions of the tank.


(sorry for the quality, hopefully we'll be able to come up with better pics in the next days.)
Judging the length of the arms is really hard, I'd say fully extended they are up to 15cm; in a relaxed position, I just can't tell yet.
Having no experience, I'm still pretty sure it's not O. vulgaris, but A. aculeatus. What would you think?

At the moment, we are happy and super excited, and hope to be able to harbor it for a couple of months.
Kristina and Benjie
*proud ceph keepers*
I would agree, not O. vulgaris and very likely A. aculeatus. There is often confusion with the use of the word, common, when referring to octopuses. the Common Caribbean Octopus is O. brieareus. The Common Indonesian octopus is typically A. aculeatus (or one of its relatives). The world wide Common Octopus is O. vulgaris.
So the octopus (still not sure about the name, but involuntarily, we beginn referring to it as "he") has been pretty seclusive. We were not able to spot him for a whole day, then found his eye peeking out a tiny cave - he even made the entrance more narrow by stuffing some debris into it. Today, he was moving around a bit - in perfect disguise of a crab. He was walking awkwardly sidewards, even mimicking the mandibles and shape of a crab's legs. It was crazy - I've upload a video for you and link it here (it takes some time to load, but I wanted to give you the details here):

You'll see that in the second video, when something scares him again, he manages to stay in character and scurries away.

It was truly unbelievable... he put on this show in the early morning, shortly after the lights went on, since then he is hiding again.

- Water seems to fine, performing 5% change each day, how long should we keep this up?
- Also we're not sure about lights for the night, we now have a very dim blue light, but I read a differnt thread (regarding a different species) that no light would be favourable...?

And to the Forum admins:
- is the video upload ok, or should I lower the quality to conserve storage space and bandwidth?
- how can I change the thread's title?

ok you shouldn't attempt to post in the early morning. got that.
where is my octopus? and where does that darn crab come from?
it's the size of a palm of my hands and never was seen in the past four months, since when the tank is cycling in...
that's very strange, and potentially unfortunate - perhaps the crab preyed on the octo. Hopefully the octo is in hiding.

Does anyone recognize what kind of crab this is? I wonder if it should be removed from the tank (although it may be too late).
Yesterday evening and this morning, the Octopus was in the tank seeming quite relaxed, moving up and down the glass in the darker part of the tank. Unfortunately, ist seems to be more of a heptapus in the moment (but hard to due to low light). The only thing I can think of ist that the crab hitchhiked its way into the tank, lived totally secluded and grew really fast. The Octopus, though, must have routed it. Apparently the got into a fight without a clear winner.

As there were no larger animals then a couple of (small) snails and hermit crabs, and those did not disappear regularly, I can't think it's top predator.

I'd love to get that damned crab out, but as it went unnoticed for months, there ist no chance of finding it without dismantling the whole tank. Give the Octo a few weeks to grow and settle in and he'll take care of business - I'm afraid that's the only strategy I can come up with.
Hi Kristina and Bennie,

It looks like you have a fine octopus and your tank looks good, too.

It’s hard to figure out the size of the octopus as compared to the size of the crab. It would be better to remove the crab if you have the chance - less danger for your octopus. Otherwise, your strategy is good.

I’ve never seen such a large hitchhiker crab in a tank before. I found one in my first tank, but it was only about an inch long and my octopus killed and ate it during her first night in the tank.

How long has your tank been up and running, and how big is it? You first mentioned setting it up in the spring. If it has cycled and your water parameters are good, you shouldn’t have to do a daily water change. You can do a 20% water change every two weeks.

I checked the first photos I took at the first day, and it seems that the octopus already had only seven arms when it went into the tank. So the crab might be excused. There is no trace of the crab anyway, also no shells which would indicate it had been eaten.

Octopus is settling in slowly, he stays mostly in the rear part of the tank, at least when observed; but we also caught him sitting at the front pane when we came to the tank. In a relaxed position, the longest arms are about 14 cm and the mantle is about 3.5 cm long.

Over the course of the weekend, he seems to have eaten one or two shrimp and a hermit crab; most of the time, he ignores them completely, even when a shrimp swims really close (5cm or so).

Still waiting for an opportunity for some decent pics...

About daily water changes, I seem to recall that @DWhatley recommended them for the first two weeks or so to minimize the risk of a loss. The tank (500 litres) is up for four months now (that's when the live rock came in) and seems fine.
So, some pics.

Here's how he spends most of his time - if he's not hiding in a den:


About the s/he question: what could be R3 (if you add the missing arm) seems to be curled most of the time, as the picture indicates. Anyone wants to take a guess?

Another pic of a pose which I never observed with O. vulgaris:


If he knows he's being observed, he mostly shows that indistinct brownish/greyish look. When I get him off-guard, though, he has a much more contrastive dark/light pattern. What he loves to display at different occasions is a narrow white stripe running down the mantle top to bottom, splitting it in two halves. In general, he seems to be mors active in the mornings than in the evenings (which would follow natural behaviour).
I just converted your 500 liter tank size to US gallons - it’s 132 gallons. That’s a good sized tank so you really would be able to have a larger octopus someday.
It’s also an advantage with a smaller octopus because your small octopus has less impact on the water quality (although you need to keep testing).

Nice corraline algae!

Here is a great shot of an aculeatus male's third curled arm,

I hope I have not confuses the concept of how much/often to do water changes. With a tank that large and fully cycled, once a week should be fine. Daily changes are only important for tanks that are too small for the animal received or tanks that received animals before being well cycled. With a 500 liter tank, the daily changes should not change the water parameters (the only real concern with too changing water too frequently) if that is easiest, no harm done but even 2 weeks (with larger changes) should be fine for the sized animal you have and a fully cycled tank that large.

I am worried it may not be eating enough and would encourage trying to stick feed half a thawed shrimp. Sometimes you have to get them accustomed to the offering and even ET will make me touch his inner suckers some days where he will come up, to the side of the tank, poke it with an arm tip and then decide he wants it on others.
These are great pics and very heplful indeed. In fact, this looks a lot different ... so probably female?

Thanks for the clarification on the water maintainance issue. We'll reduce that to weekly 10% change for now.

It was our plan to start srick feeding today, although I'm afraid it's still to shy for that... we'll see.

May I ask again if we should keep the dim "moonlight" LED or put it away completely?
May I also ask again how to change the thread's title?

Thanks to all, we really appreciate the support here!
Oops, missed those questions. Let me know what you want as the title as only an moderator can change them (not sure why). Typically, I try to have members include the animal's name and species as the title so that anyone searching by either can easily find the thread.

Any night lighting should be red. No lighting is fine but if you want to observe at night red will not disturb the natural night awareness. For nocturnals, I recommend leaving a red light on all night but for diurnals leaving the tank totally dark after human bedtime is probably best. IME, red light does not seem to bother the nocturnals but they can detect it and will often wait for full lights out to hunt if there is an option. I don't recommend using blue moon lights at all. It may be that blue is actually bright to their eyes than white. For diurnals, blue or white all night is definitely stressful. One color setable nightlight we had would revert to blue if the power went out. We had a lot of thunderstorm related short outages while using it and it took me a few times to realize my octopus was nervously pacing when he should have been sleeping because the color had changed. After about the 5 time we saw him stressed, we eliminated that light.
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