[Octopus]: Megamind - O Mercatoris(?) Hitchhiking Octopus

Jan 19, 2015
Dominican Republic
Hey everyone I am attaching this here from another forum where I requested an ID on this fellow and was directed to this amazing forum. This is how the story starts:

About two months ago I noticed my sump/refugium slowly becoming a shell grave, snails were being consumed as well as small crabs and hermit crabs. I thought I might have an aggressive gorilla crab or really anything "aggressive" but what I found two days ago. When I turned on the lights of the sump/refugium I saw this little fella darting into the darkness of the sheltering rocks. It's about 3cm in diameter so pretty small I think. I'd like to know what everyone thinks about keeping octopuses and their danger to other tank inhabitants. I've read very contradicting information regarding this subject. This little guy came along some live rock I picked up in Ocoa Bay, which is in the Dominican Republic, where I live. My plan is to return it to Ocoa Bay next time I go back but is there any possibility I could sort of "rear" it until it grows a little more. It looks so teeny and defenseless...
I know these picture aren't the best but you can see its coloration and somewhat tell skin pattern. He's pretty fast and hides once the lights go on, my lens is manual focus so yeah... I hope someone can ID this little fella. Any info about this little guy would be great, otherwise I'm just scrounging the web for info.
DSC_7961.jpg DSC_7963.jpg DSC_7964.jpg DSC_7967.jpg
I'd love to keep him and will do so until he becomes too big. I will have to research on octopus proofing the tank and I'm going to be aquascaping the DT so he has more places to hide. He's currently in the sump (where I found him) which is a 50 gallon and it's huge for his size (though I know the ocean is bigger so maybe it's actually small...). If anyone else knows anything about this little fella I sure would appreciate it.
I'm currently moving some things between my 50g and my 100g so that he or she can have a mostly his/her own tank. I don't see the octopus often just a few glimpses before I turn on the sump light But I can tell it's eating what i've put in for it which are crabs, snails, and a few small mollusks I caught in the same area where I got the live rock this little fella hitchhiked on. I have a friend who works at the local aquarium so when [Megamind is what I'm thinking of calling it] gets too big, he can live at the aquarium and I can check him out every now and then.
Nikky, Megamind is adorable.

Looking at the accentuated eyes, mantle to arm length and coloration I am guessing a nocturnal dwarf that will not out grow a 30 gallon tank (but you do have to octoproof it). The eyes look a bit prominent for an O. mercatoris but we see them in south FL and they are likely to be common in the Dominican Republic. The only octopus that I KNOW is common to both (or I should say to Hatti and FL) is O. hummelincki (Megamind is definitely not hummelincki) but I suspect O. mercatoris as well as O. joubini are likely also common. O. joubini is also a red nocturnal dwarf that is often confused with O. mercatoris but I have never found a clear description of the visible differences (I believe O. joubini has longer arms, know it is a small egg species vs the merc large egg size and may be a bit more active). Some of the best in-tank images we have of O. mercatoris can be found in this older journal by gholland and @Neogonodactylus has the best detailed lab shots in the photo Gallery.

As far as controversy about keeping an octopus in an aquarium. Please feel free to mention where you have seen opposing thoughts and we will try to give answers based on the experiences we have had over the years.

Something I feel I should mention is that once an animal (which includes corals and even LR because of the animals within) is removed from the ocean and placed in an aquarium, it should not be returned to the ocean, even if it means the death of the animal. There are public aquariums that will do this but they run flow through systems (ie the water in the tank is piped in from the ocean) and nothing foreign to the water is ever placed in the tank. Returning an animal risks exposing others to harmful bacteria or invasive species.
As an aside, one of the tank items I have found to be excellent for O. mercatoris is a collection of giant purple barnacle shells placed roughly at 1/3 of the tank height (from the bottom, 2/3 water on top). If you place these so that you can see in but the octopus still has a dark den, you will see more of it than if it uses crevices in the LR. There is no guarantee it will choose the barnacles, but all my females and most of my males found and chose this arrangement for their homes.
What a charming little octopus! I"'m glad you have a tank for him. D is right about barnacles - not only do they provide good places for your little octopus to hide, but they look nice in your tank!

Wow thanks very much D. I'll take your advice on the barnacles. I had originally thought of taking Megamind back to Ocoa Bay after growing but I've received enough advisement against it. I hadn't thought about what I could introduce into the ocean from my system. If it comes to odds, which I don't think will happen, I can always take him/her to the aquarium where my friend works. I have to see about octopus proofing without inhibiting gas exchange.
Again, thanks D and Nancy, this is a lovely ceph community. I will update periodically or maybe start a journal for Megamind.
I found the ReefCentral thread you referenced and was pleased to see someone there also mentioned the concerns about "returning" animals to the ocean after exposure to an aquarium. It is not one of those obvious concerns until you think about it.

I hope you had a chance to read and view the images for gholland's little hatchings that I linked in my first post (new members often miss the underline and coloration marking a link). I believe you will see the similarities with Megamind. However, keep in mind that even experts are fooled with these animals and only longer term observations (and sometimes only by necropsy) confirm what species you are observing. Fortuantely, care for shallow warm water animals is similar enough to give confidence to the keeper.

PLEASE do journal your adventure. I can easily move the thread to the journals forum if you would like to use it as the beginning.
I did check out the journal, they seem very similar. I realize misidentification is possible but it does seem pretty accurate.
Please do! I think I would add this anyways when I create a journal so if you can move it that would be greatly appreciated :biggrin2:
I've been trying to offer Megamind food and see if he gets used to me so he won't dart out of sight all the time. He stayed out longer today watching me or maybe he was just sleeping. I got another nice shot of his tentacles since he likes sticking to bottom left corner of the glass a lot. And his bulgy eye came out too, observing me I think. I was surprised that he actually gave me time to manual focus before leaving but once he left, he was gone gone. I could still see him under a shelving rock, but my camera couldn't. Oddly enough his eye didn't look at all like in the previous shots but I guess that's due to their ability to change color/texture unless there are two octopuses which I highly doubt. Here's Megamind.DSC_8014.jpg
Looking more and more like O. mercatoris. The little "eye lashes" under the eyes are considered one of the attributes of this (but not ONLY this) species.
So I was dangling a small live crab in front of Megaminds cave, I could see him watching me from the small gap and he waved two tentacles out of the hole next to his cave entrance. He did the waving tentacles twice, I looked down for a second to take the lens cap of my camera and the sneaky little guy grabbed the crab and ducked back I to his cave with it. Lol. I did manage to get a picture of his ever watching eye, I'll post it later today. He looks less tiny than when I first spotted him. He was the darkest red I'd ever seen him when he snuck out of his cave to snatch the crab, I wish I'd gotten that picture :P I wonder why though... I've read they turn white when they become scared, I've usually seen Megamind red. I'm gonna read up on what we know about specific color changes (besides obvious camouflage). He's eating about 2 hermits or small crabs a night, I guess any appetite is a good appetite?
I'll give more updates soon!
Eating is always a good thing. How much and how often is not well established. My personal opinion is that the frequency depends a lot on if it is a warm or cold water species AND the age. They grow very rapidly in the 4-5 of months (guessing Megamind to be around 2 months) so my thinking is, give them as much as they will eat daily.

You can feed live food throughout their lives but many of us do not have regular access to live. Food size does appear to matter and my best successes with dead food is to begin by offering eye sized pieces and slowly increase to about 1/2 mantle size as they adjust to the accepting dead food. Live food should not be larger than mantle size and I suggest about half that. The mercs I have kept have all been less adapting to frozen than the larger animals but have learned to eat freshly killed (they don't seem to be able to catch them once they are adults) shore shrimp and frozen fiddler (or any small - be sure there is no smell when freezing) crabs. I have also had good luck feeding young and very old animals (they only live 10-12 months) with frozen Cyclop-eeze but it is no longer available to hobbyists because of a failure at the collecting source. You can try a variety of fresh/frozen marine foods including small pieces of fish, clams on the half shell (larger animals can open them but I have not seen the dwarfs able to do this), crab claw meat (I freeze freshly collected blue crab claws - NOT THE WHOLE CRAB then extract the meat and thaw before offering). Claw meat can be extracted and offered on a stick (you can try hand feeding once he is fully acclimated). Crabs offer the best nutrition and should be a mainstay of their diet. I have not had any luck with abalone, recommend avoiding oysters and mussels because of the mess. IME, thawed frozen scallops seem to be accepted once and then ignored.

A tripod and remote firing device (if you camera can accept one) are recommended :biggrin2:
sorry for the super late update, my internet was down for a few days. here are the pictures ive taken of Megamind. He's eating well, I catch crabs and small shrimp from where i got him to feed him. The crabs are slow and he catches them quickly but the shrimp are quicker and take him longer. I've noticed he has an appetite for my cleaner snails, from Ocoa Bay like himself, so I throw him in a few sometimes. DSC_8040.jpg DSC_8060.jpg DSC_8064.jpg DSC_8065.jpg

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