Day Octopus

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Species group:

Other common names: Big Blue Octopus, Cyane’s Octopus

Scientific name: Octopus cyanea

The basics:
Because it hunts by day and is very active, the aptly-named Day Octopus is much in demand among Octopus fans. Serious aquarists find it a challenging but worthwhile pet, but those new to the hobby are better-off starting out with a smaller, hardier species.

This widely-distributed Octopus ranges from East Africa across the Indian and Pacific Oceans to Hawaii.

The Day Octopus is most commonly associated with coral reefs, but may also be found around rocks and wrecks.

Appearance / health:
The stocky mantle (head and body) averages 16 cm (6.2 in) in length, and the arms may reach 80 cm (32 in), providing a total arm-span of 1.5 m (5 ft). The skin color is usually some shade of brown, with darker brown appearing on the arm tips and oval false eye spots (ocelli) at the base of each arm. Even by Octopus standards, this species has stunning camouflage abilities…one individual was observed to change color 1,000 times in a 7 hour period!

The Day Octopus’s natural life span is only 12 – 18 months, and it is extremely sensitive to copper, ammonia, and nitrates in the water. When startled or stressed, Octopuses release a black, inky liquid designed to confuse predators. In the confines of an aquarium, however, ink can prove fatal to an Octopus.

Behavior / temperament:
Octopuses are surprisingly-intelligent, quickly figuring-out how to extract food from closed jars, distinguish shapes, and recall what they have learned. Several species have been observed to leave their aquariums, negotiate floors, catch shrimp in other tanks, and return to their home base!

No Octopus, however calm, should be handled or hand-fed, as all produce venom and can deliver a painful bite with their hard, curved beaks. While fatalities from the commonly-sold species are unknown, the possibility of a serious allergic reaction to their venom must be considered.

This extremely active Octopus requires a well-filtered 200 gallon or larger aquarium that has been cycled for 2-3 months and is provisioned with a thin layer of sand. They are stronger and more determined escape artists than most, so the filter canopy must be weighted or secured with clips and duct tape, and all hose/wire openings must be sealed. Wet/dry and other out-of-tank filters are the best options, and a protein skimmer is advisable.

Lighting should be subdued; a red night-viewing bulb will allow you to observe your pat’s nocturnal wanderings. Caves, preferably of live rock, are essential. Clay flower pots, empty shells, and other shelters will also be accepted. All rockwork must be secured, using silicone if necessary, as Octopus are incredibly strong – and they seem to delight in trashing whatever homes we provide for them!

The Day Octopus should be maintained at a specific gravity (salinity) of 1.025-1.026 and a pH of 8-8.4. They fare best at 23-27 C (73-80 F).

Youngsters and newly-caught adults often refuse all but live shrimp and crabs; green, fiddler, Asian shore, and other crabs may be collected or purchased at bait shops. In time, most pets can be weaned to non-living foods. The diet should be varied, and include crabs, clams, mussels, scallops, snails, abalone, and spearing and other fishes and invertebrates.

Captive breeding is rare, with fights and/or predation being the usual result when two individuals are introduced. Female Day Octopuses guard their many thousands of eggs within coral crevices or other shelters, and usually expire shortly after they hatch.

Written by Frank Indiviglio

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