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Recent hatchling give-aways by Massachusetts student suggests that they don't do well as hatchlings in a small tank (she saw serious missing arms and other damage). Zyan Silver was successful with larger tanks and did keep a pair of the hatchlings together through breeding adult size (we don't know what happened after that). Sibbling mercs and very likely same sized animals have been kept together and have produced offspring but we have not seen success with multiples of other species in an aquarium partly because of the size tank that would be needed just to try and partly because there is a high chance they will kill each other. All mixed species pairing have been serious failures.
The student in Mass found that her hatchlings were attacking each other and worked at separating them. Whether they would cohabitate as they grew is unknown. Since Zyan did not see the same kind of attacks, it may be that with a large enough tank animals of the same size would live together. We know animal size makes a difference, we don't know if they must live together as hatchlings to accept each other in a tank environment. An alternate method, used in the lab is to keep a male and a female in separate environments an then introduce the only for mating. This was my approach for the tank raise O.briareus animals I raised and mated (successful matings but unsuccessful survival of the hatchlings).
We see lots of hatchlings from WC fertile females but little survival. Most of the hatchlings are from small egg species and there is extremely limited success with any of these in the large aquarium and lab environments and litterly none in the home aquarium hobby. Bimaculoides is a large egg species so there is opportunity to raise hatchlings and Zyan's success was greater than GHolland and my own with the mercs (and with O. briareus for me this last year) in terms of numbers. Octopus keeping is a relatively new hobby and we are still learning.