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general info needed on O. mercatoris


Nov 25, 2007
Hi guys and gals, I’m in need of some general info about my newly found hitchhiker. He had to have came with my live rock from Tampa Bay Saltwater that I started my 90G mixed reef with 7 months ago...the thing is I didn't even now I had him until a few days ago. I was scanning the tank with my red-lensed flashlight as I have done almost every night since starting the tank and boom, he was just sitting on this rock. I had to wake the wife up so she could see him and snapped a few pics.

I've had the tank stocked with a clean up crew for about 6 months and have had 5 fish for the last 5 months. The blue-legged hermit crabs have been disappearing slowly but I also have a few gorilla crab hitchhikers that I haven't been able to get rid of so I chalked it up to them. I have also lost a few astrea snails but I know they have a problem righting themselves sometimes. My fish haven't been touched and are a large 4" gold stripe maroon clown, flame angel, royal gramma, sixline wrasse and a watchman goby. The last 4 were all bought at about an inch to an inch and a half in length and are now between 2 and 2 and a half inches.

Should i fear for my fish since spotting the gulf dwarf octo? I was told that they do not live very long but have heard three different life spans, 6-8 month, 8-12 months, and 2 years...which is correct? I have attached a pic and the colors are way off because it was taken using the red flashlight...so it was either this color enhanced one or a black and white. Thanks for any info you can give me.

:welcome: to TONMO. Check out Dwhatley's posts about here merc "Trapper" and her offspring for a lot of merc info. 7 months is pretty old for a merc, you may be seeing the octo out and about a bit more because it's near the end of its lifespan. I suspect if your fish have been OK 'till now, they're probably safe, since the octo isn't likely to get much bigger, and if you keep it happily fed with crabs or shrimp, it'll probably not change its feeding habits.

It does look more like a merc than any other Atlantic octo I can think of, but it'll be interesting to see if the ID expert types agree.
If your octo is 7 months old then it is definitely pygmy and most likely Mercatoris (patterning and posture look right). I would not fear for any of the tank inhabitants as mine would never eat even fish fry and don't do a lot of hunting. If you want to see your little guy more often, try squirting in a little Cyclop-eeze (frozen, not dried) about an hour after lights out. If you can mount a red light on the tank, you can leave it on all night (or just try it at feeding time) to enjoy your little hitch-hiker. Jury is still out on my lot as to their natural life expectancy. My tank raised female brooded and hatched her young at 8 months. If she does as well as her mom (and I don't think she will as she has not eaten as well during her brooding) she will survive another 2-3 months (more typical would be 1 more month). When you see your little guy walking around during the day, you will know it is within a week of the end, until then, enjoy your hitch-hiker!

If she/he starts showing up for food, try offering a dead (recently killed) mithrax or fiddler crab at the end of an air line or other clear tube/stick. Eventually, Trapper (my original WC female) would prefer shrimp or crabs given by hand. Welcome to the world of cephs - hope you get hooked!

PS, never thought about covering my flash with a red film. Miserable color but it would allow me to feel better about trying flash photos! Do you know of a lense filter that would adjust the color?
It is most probably O. mercatoris and is probably nearing sexual maturity.

There are several LED flashlights on the market with red elements. They provide a "pure" red light that should be fairly dim to an octopus. I usually use one of the red keychain LEDs. They are usually bright enough to see into a tank.

dwhatley;105477 said:
PS, never thought about covering my flash with a red film. Miserable color but it would allow me to feel better about trying flash photos! Do you know of a lense filter that would adjust the color?

D, I read through your thread on trappers offspring last night and that's some very cool stuff! I know a cyan filter would absorb red but I really cannot say what kind of results you would get. I have always had white moonlights over my tank and use the red light to see back into the rocks. I wanted to watch him as long as possible so I didnt use a flash to photograph him.

My first thought when seeing him was...great he's gonna eat all my fish! Then I figured if I could feed him maybe he wouldn't bother them so I thawed a peice of shrimp and fed him with my airline feeding tube. He grabbed it quick and dissapeared into the rocks. I was kinda hoping that since I fed him he would come back out but it's been 3 nights and I haven't seen him again.

Thanks everyone for the info...I'm feeling better knowing it's a good chance he won't bother the fish. Now i'm anxious to find him again!
I'm adding your hitchhiker to the List of Our Octopuses at the top of Journals and Photos. Have you thought of a name? Otherwise, I'll just put "octopus".


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