I have very limited experience, so I can only speak about what I’ve specifically done, and how it’s worked out. I’ve been keeping a young wild caught Bimac in a chilled 60 gallon tank for about two months, with various tank mates, and I can tell you how the various pairings are working out. Since 100% of my experience has been with this one individual octopus, and 100% of the tank mates have been animals that live around bimacs in the wild, you (and I) should hesitate to draw more general conclusions from what I’ve experienced. My bimac has about a 2 ½” mantle (assuming you don’t count the eyes in that measurement) and I would guess it is about 30% grown. Here’s what I’ve tried, and how it’s going:
Sunburst (or Solitary) anemone (about 5” total width when open)
Totally compatible. Various things I have read on Tomo said “no anemones”, but these anemones are everywhere in the place I caught my bimac, so it seemed reasonable to assume that bimacs can deal with them. The Bimac tries not to touch it, but occasionally does anyway. He quickly pulls back, but not frantically, and there’s no damage, to the bimac’s skin, or change in behavior. The reaction is about the same as when I touch my heated plate at the Mexican restaurant. I pull my hand back quickly, remind myself not to do that, and then go on with my day. No big deal.
a 6" rock encrusted with Strawberry anemone (3/8" each).
he doesn't seem to mind touching these guys at all, and treats the rock like a rock. completely compatible.
Peppermint striped shrimp, 1” long
I can’t imagine why this shrimp didn’t become bimac food immediately, but the octo ignores the little shrimp
Chestnut cowry – 1” long
Bimac ignored it for a couple of weeks, but when I was experimenting with lower feeding amounts, and he was really hungry, he tried to eat the cowry. That was a big problem because the cowry’s defense was to put out a huge amount of slime into the water. It made a big mess in my 60 gallon tank. No cowries.
Red gorgonian – 7” tall, 9” wide, 3” thick
The gorgonian is a leathery coral that looks like a bush with tiny little polyps that make it look “fuzzy” when they are out. The octopus ignores it. He bumps into it sometimes, but does not react. Totally compatible
Spiny sea cucumber – 6” long
The octopus ignored it, so they are compatible, but my sand is wrong for the cucumber and it wasn’t getting enough to eat so I took it out. Also, I plan to get a leather star, and those eat sea cucumbers. Oh, I should mention that unlike some of the warm water sea cucumbers that can poison a tank, these southern California cold water varieties are safe (according to David Wrobel’s book)
Norris’s Top Snail – 2” diameter
The octopus didn’t eat it, but he bullied it a lot and kept pulling it off of the glass and dropping it to the floor of the tank. I think it was a fun game for the Bimac. This matchup might have worked in a much larger tank with lots of other things to keep the octo’s interest, but basically not a good match. However, I expected the big snail to be instant food, and it is interesting that it was not.
Fish - Tide pool skulpin – 2 ¾” long
This is a little bottom fish that is very abundant under the same rocks that I caught my bimac under. The bimac chased it around half heartedly for a couple of days, but the fish just jumped out of the way as if brushing a pesky fly away. After the first couple of days the bimac realized that it would never catch the skulpin and seldom tries anymore. I think the skulpin takes it all in stride. Totally compatible (at least with an octopus this size and age)
Fish – opeleye perch – 3 ¼” long
This fish swims all the time, and can easily keep away from the octopus. No problem
Brittle Star 5” diameter
They totally ignore each other – totally compatible.
3” diameter thick shelled rock scallop
I didn’t know if this would be a tank mate (too big/thick for the octo to open) or food. It was aggressively and successfully attacked. The bimac seems to find all clams to be irresistible food.
purple sea urchin - 1 1/4" diameter
This spiny little guy is perfectlly adapted to living with an octopus. The octo felt him gently a couple of times, and immediately gave up. They ignore each other - totally compatible.
Note: things like this urchin, and the anemone, while not a danger to the octopus, take up tank space, and create no-touch, zones in the aquarium, so it is important to keep them small, few, and out of the octopus's way (in the corners). If a few of these things are spread evenly in the tank, then the octo's world becomes a bit like a mine-field, and he has to alwasy watch where he steps.
That’s my experience so far. I don’t know how useful it will be for you. Since I’m putting species together which have lived together in the wild for millions of years, the likely hood that they will know how to live together is much higher than if I were bringing things home from the fish store. Also, my track record is only two months long, and my bimac is immature, so I may have a different story to tell in a few months. That being said, my experience does support the idea that there are exceptions to the conventional wisdom, which says things like “no fish”, “no anemones”, “and no sea cucumbers”. Before you start experimenting, remember that I had two unusual advantages:
1) All the tank mates I tried had evolved right beside my species of octopus, and so the two had each evolved ways to deal with each other. Your results may vary.
2) I get my tank mates for free, so I can afford to experiment, and if a tank mate turns out to be octopus food, or even if my octopus turns out to be tank mate food, it’s not the end of the world. Recovery from even a worst case scenario for me (everything dies) would literally be a day at the beach, catching a new octopus, and tank mates. (I am of course prudent and responsible, and take great care to prevent harm to the animals I collect (except the food animals, like shore crabs, for which causing harm is an integral part of the plan). I do lots of research before I bring anything home, to ensure that harmony in the tank is likely, and that animals are at least as safe in my tank as they would be in the big bad ocean, so please don’t think I’m advocating unethical or irresponsible treatment of animals.)
I hope some of that is helpful, or at least interesting.