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Cohabitants of giant pacific octopuses in captivity<< Cephalopod Articles | By Dr. Roland Anderson
Within the last four years, the Seattle Aquarium opened two large exhibits in succession dedicated to the giant Pacific octopus. Both were about 3000 gallons each and each had a different theme. The first depicted the habitat under a Seattle wharf and the second a rocky reef. The second was part of a larger exhibit dedicated to the Life of a Drifter (octopuses spend a considerable portion of their lives as part of the plankton). The second exhibit was also an attempt to improve interpretative opportunities at the display—a large emphasis of the Aquarium's programs.
As part of the enrichment opportunities for the octopus and to present a naturalistic habitat for it, both exhibits had cohabitants in addition to the featured octopus. These animals were chosen carefully in an effort to find animals that would not be eaten or be harmful to the octopus. As part of this effort, we did a survey of aquariums via the email list of aquarists, the AquaticInfo List. A reasonable number of aquariums responded. Their information is added to our own experience in Table 1.
Most animals reported living in tanks with GPOs were rockfish and sea anemones, especially black rockfish and plumose or Urticina anemones (see Table 1). Black rockfish are an off-the-bottom schooling species and are thus less prone to getting eaten than the benthic rockfish species, those living on the bottom among rocks. Other species of rockfish have been kept with octopuses relatively successfully but if the tank is too small or the octopus is hungry or has an aggressive personality, it can catch just about any fish, even salmon. Sculpins are particularly prone to getting caught and eaten (see photo 1) since they are slow swimming bottom dwellers.
A number of invertebrates have been successfully kept with GPOs, such as sponges, sea anemones, sea pens, chitons, small snails, limpets, sea stars, sea cucumbers, sea urchins and tunicates. No bivalves, large snails or any crustacean (other than barnacles) can be considered safe in an octopus tank; GPOs can and will eat them.
Two species of sea stars should be avoided. The sunflower star (Pycnopodia helianthoides) has been implicated in many fish and invertebrate mortalities, especially in closed systems. It likely releases an undescribed toxin into the water. The slime star (Pteraster tesselatus - "snot star" in the vernacular to aquarists) releases copious amounts of clear mucus when disturbed. Most other sea stars are probably safe for the octopus tank.
GPOs have eaten a number of different fishes in their displays, even dogfish sharks (Squalus acanthias). Animals to replace those eaten must be collected or bought and shipped, sometimes at considerable expense. This list was compiled to help other aquariums exhibiting GPOs decide what auxiliary animals they can safely keep in their display.
I thank all the aquariums that contributed to this survey.
See Table 1. Animals living in Giant Pacific octopus tanks.
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