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Suspected mercatoris (and if so..)

Jan 12, 2019
Hello everyone!
Received the long awaited call from the LFS and picked up a little octopus that seems healthy. From what I can tell, he(?) looks most like O. Mercatoris, but I wasn't sure. Still waiting to hear from the guy about where they ordered from. Any thoughts? M/F, Species, etc.
Also if it is a mercatoris, I thought they preferred a smaller tank, and I have a 90 gallon with about 70 lbs of LR. I did see him(?) yesterday around 9pm by shining a red light for about 20 minutes with all other lights out. Am I going to have a constant hider, and is there anything I can do about it? Also any input on feeding a really small octo would be great. He rejected the tiny piece of krill I offered. I have some ghost shrimp in a freshwater tank, but they're pretty big compared to the octo.


Staff member
Sep 4, 2006
Interesting octo. The closeups seem to show a black dot above each eye, is this a valid and consistent observation? If so it would be an identifying clue but not common to O. mercatoris. It also appears to have a large unpigmented section along the dorsal side of the mantle. This is worrisome as the one time I have seen something similar happened because the animal was exposed to extreme cold. It would indicate a damaged area but may not be recent.

I would consider a smaller home if you can capture it without harm. If you can locate a cluster of giant purple barnacles, you might have success with a den choice for either observation or relocation.
Jan 12, 2019
Still doing well, Marcus Aurelius (I'm just gonna assume male) has been I think crepuscular? I see him under red light at about 8:30pm and he's been taking some ghost shrimp, clam pieces and eventually frozen krill. I contacted the store about where he came from and they just told me "pacific" Well, that's not super helpful, so I'm just waiting for any identifying characteristics. I think I have a young one, but not totally sure. I had the tank at 74.5 F for the first few days, but after reading some posts here I turned off my fan and the temp climbed to 79.0 F over a few days, which I thought was closer to a tropical pacific environment. My dad took a picture under red light and managed to edit the colors so that the Marcus is much more visible

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