
The Bricks,
Why joubini? For many years O. mercatoris has been call
O. joubini but
O. mercatoris is a large egg, relatively common octopus (though we have not seen many in the last few years) where
O. joubini lays small eggs, is likely slightly larger and rarely available. Both are nocturnal dwarfs and quite reclusive (anecdotal observations suggest that
O. joubini may be more active). A 65 gallon tank would be overly large for a single specimen of either.
Your 65 would be suitable for a medium sized animal (
O. hummelincki, A. aculeatus, O. briareus) that will be more active, live to be somewhat older and seen more often.
Sourcing any octopus is a challenge. Some LFSs will order them for you and occasionally you will see them available on-line. Ordered animals are most often imported and frequently in the Abdopus group (often aculeatus) or a nocturnal we believe to be
Callistoctopus aspilosomatis.
Here is a short list of links I recommend to all new octopus keepers. The Box of Chocolates thread gives a bit more detail on what to expect when you are octopus shopping.