50 Gallon would do...at adult size they reach a mantle length of 12 cm. (4.5 in.) and a tentacle length of 60 cm. (2 ft.) with a total of approx. 2 1/2 ft. I believe their tropical because their native to California coasts and Florida. They are known especially for their long tentacles and known as Carribean Reef Octopuses.kingsnar said:Is Octopus briareus notcurnal? Tropical? Lifespan? How large and what size tank?