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Bimac size and feeding question.

Backs

Hatchling
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Aug 31, 2007
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I've been setting up a salt water tank fairly slowly but this Friday I'm going to have the last of the live rock I wanted to buy for it (i'm getting 90lbs total) and am going to leave my tank to cycle until the summer before I put anything in it. It's a 75 gallon which I have read is more than big enough for a bimac which I hear most people keep in 50 gallons, but I still have some uncertainties about this Octopus. From what I've read, the Bimac can have a mantle length of up between 5-7 inches and 23 inch tentacles, but from the pictures and different posts I have read I've never seen one that looked to even be close to that big to me. I've heard many things on these particular octopuses and I've heard of many people having them be 7 months old and only having a mantle the size of a golf ball which comes nowhere close to 5 inches let alone 7. Do Bimacs actually get this large or are some of these smaller octopuses not actually Bimacs or what? This leads to my further question about feeding a full grown bimac if they get as large as I've read that they do. I have no problem having a supply of some small fiddler crabs and have a 20 gallon that I'd keep them in and can keep filtered between feedings, but most fiddler crabs I've seen are maybe 2 inches long at the max, so I don't see how a full grown bimac could make a meal out of such small crabs. Do bimacs just not get as large as I read or do you just have to feed them larger things than fiddler crabs eventually? Thanks
 
Keep in mind that octopuses dont have bones, so they can stretch quite a bit, 23 inches arm legnth is probably about ttwice the size of their arms on a normal day, I also think those dimensions might be a bit bigger, but an octopus of that size could probably become as small as a softball. Bimacs are currently very hard to get, however you can get some very similar species quite easily, such as hummiliniki(sp?) and abdolfus(major sp?). Any octopus that you can keep in a tank of that size will be able to "make a meal" out of a fiddler crab.
 
There are two different bimacs, O. bimaculoides and O. bimaculatus.

O. bimaculatus supposedly grows considerably larger than the other. Either way it would be fine in a 75. You have to consider that in captivity their diet is going to be different, water conditions are going to be different, etc. So, they may never reach their potential size. Not to mention the weaker of the babies are going to be weeded out in the ocean, whereas a "runt" may live out its full lifespan in a tank without predators and a steady supply of food, no competition.
 
The main difference from everything I've read is that O. bimaculoides is a large egged species so the babies are relatively easy to raise and the other is a small egged species. Other than that, it's practically impossible to tell the difference between the two. I'd have to say from my observations of others journals on here that every species of octopus is going to have its share of personable and antisocial individuals. My mercatoris for example was VERY shy, secretive, and never cared much for my presence. On the other hand, Dwhatley's group of mercatoris' all have different dispositions. Abdopus aculeatus has a reputation for being very day active and interactive, but the one I kept was very shy and only came out to hunt when no one was around.

I think people probably prefer whatever they can get their hands on. Neither of the two bimac species seem to be readily available. Anyone who insists that the only species they want to try is a bimac should just wait for someone on here to announce captive-bred ones. Otherwise ordering a "CB bimac" online is a gamble.
 
Is anyone in the forum currently raising Bimac for sale or another species that is similar? I am setting up my tank now and I am looking for one for late August early September?
 
hummelinicki. they are diurnal and mine was interactive. or you could try a. aculeatus. my a. aculeatus is more interactive than my hummelincki.
 

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