Octopus mercatoris (Pygmy Octopus) Care Guide
Octopus mercatoris is a small nocturnal Caribbean octopus kept by advanced aquarists, with a short lifespan and demanding husbandry.
Compiled by Aquairi from published sources · Published · Updated
Overview
Octopus mercatoris, the Caribbean dwarf octopus, is a small cephalopod of the family Octopodidae, described in 1937. It is among the smallest octopuses kept in home aquaria, nocturnal, and rarely seen despite being locally common.
Taxonomy
- Family: Octopodidae
- Order: Octopoda
- Class: Cephalopoda
- Scientific name: Octopus mercatoris
Habitat
It inhabits the Caribbean Sea region of the Atlantic Ocean. The species is mainly nocturnal, hunting by night and sheltering in a cave or rock crevice by day, and is sometimes found in small groups under rocks.
Tank requirements
- Minimum tank volume: 80 L
- Temperature: 24-26 C (75-79 F)
- pH: 8.1-8.4
- Carbonate hardness (KH): 8-11 dKH
- Specific gravity: 1.024-1.026
- Housing: solo, with an escape-proof sealed lid
Diet
It is a carnivore feeding on crabs, shrimps and small fish. In captivity it is fed fresh meaty foods and kept alone, as it is a predator.
Breeding
The species has an average lifespan of about 8-10 months. Because its eggs are large, it is sometimes kept and bred by aquarists, though success is demanding and the parent typically dies after brooding.
Pygmy Octopus (Octopus mercatoris): Breeding Guide
Overview
Octopus mercatoris is a small Caribbean and Gulf of Mexico dwarf octopus and is the pygmy species most often encountered in the United States hobby. It is nocturnal and reclusive, denning in shells or rockwork. It is one of the few octopuses regularly bred in home aquaria because it is a large-egg species whose young hatch as crawling benthic juveniles rather than drifting larvae.
Sexing
Like other octopodids, mature males carry a modified arm (hectocotylus) used to transfer sperm, while females are recognised once they begin denning and laying eggs. Because the species is small and short-lived, sex is often confirmed only in mature animals; wild-caught females may already be carrying viable sperm.
Breeding Setup
A fully cycled, escape-proof saltwater system in the 15-25 gallon range with ample live rock is used. Hobby reports note that females readily den in sheltered structures placed roughly a third of the way up the tank, and dim or red lighting suits this nocturnal animal. A female that mated in the wild has a good chance of producing fertile eggs if she broods within about four months of capture.
Spawning & Egg-brooding
The female lays large eggs inside her den and broods them continuously. Documented hobby broods ran for roughly four to six weeks of brooding and produced small clutches, with examples of about 6 and about 25 hatchlings. The species is semelparous: the female does not feed while guarding the eggs and dies after they hatch.
Hatchling/Juvenile Care
Because development is direct, hatchlings emerge as miniature benthic octopuses, around 1 cm mantle length, with no planktonic stage. They hunt immediately but are fragile; losses are heaviest in the first week, and the main difficulty is offering appropriately sized live food with adequate nutrition. Multiple successive captive-bred generations have been raised in the hobby.
Common Challenges
- Finding live prey small enough for newly hatched juveniles and getting them to feed.
- High first-week hatchling mortality even under good conditions.
- The short adult lifespan and semelparity mean a single brood ends the female's life.
- Strict escape-proofing is required, as octopuses readily leave open tanks.