What is the smallest interactive octopus species?Simple answer, keep your fingers away from its mouth. Actual answer, it is unlikely you will get bitten from small octopuses. They are curious and will grab your finger but IME, they will determine you are not food and not bite. NEVER restrict the octo so that if feels trapped or cornered. Try to stay relaxed if it grabs you. I have been tested with nibbles but never had the skin broken. HOWEVER, we have a thread about being bitten so it does happen. Allergies can be a serious problem. Unknown species and known lethal animals are an unwise pet.
This species probably has the largest range in sizes of any we keep. At one time (and I can no longer find the reference) it was actually classified as a dwarf (though bigger than an O. mercatoris by twice). It is now classified as medium. ET is in a 60+ with 35 sump and uses all of it. A 55 with sump would still do fine but I would hesitate on going smaller, especially if the tank was not long (ie the popular cubes would not give enough swimming room IMO. I think tank length is an important consideration for all but the mercs.What size tank is necessary for a hummelincki?