Adding Octopuses to Your Tropical Fish Tank

Why Octopuses Make Unusual but Rewarding Pets

Octopuses are among the most challenging marine animals to keep in a home aquarium. Many keepers and marine biologists consider them among the most fascinating too. These animals display problem-solving abilities, recognise individual people, and often develop distinct personalities. Some will dismantle tank equipment out of apparent curiosity, while others learn to unscrew jars to reach food inside.

Unlike most fish, an octopus may actively interact with you during feeding time or when you approach the tank. Some keepers report their octopuses watching them move around the room or reaching out to touch their hands during tank maintenance. You will not get this kind of response from a clownfish.

However, the commitment comes with a significant emotional cost. Most octopus species suitable for home aquariums have a natural lifespan of around one to two years, with some variation depending on species. The common octopus (Octopus vulgaris) may live slightly longer under good conditions, but even so, you may only have months with your pet before it reaches the end of its life. For many keepers, the short time together makes the experience bittersweet, so it is worth considering whether you are prepared for this before you begin.

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Finding and Identifying the Right Species

Sourcing an octopus in the UK can be difficult. Most high street aquarium shops do not stock them regularly, and those that do may have limited knowledge about the species they are selling. Misidentification is a genuine problem in the trade.

Several species turn up in the UK market from time to time. The common octopus (Octopus vulgaris) occasionally appears, though it grows large and needs a substantial tank, making it unsuitable for most home setups. Smaller species such as Octopus mercatoris (sometimes sold under various common names including Atlantic pygmy octopus) may suit keepers with less space, though they can be harder to source and are often nocturnal.

There is a serious safety consideration here. The blue ringed octopus, native to the Pacific, is one of the most venomous animals on the planet. A bite from this species can be fatal to humans within minutes. In the UK, selling or keeping these animals requires a Dangerous Wild Animals licence, making legal sales extremely rare. If you are ever unsure about what species you are being offered, do not buy it. Ask the seller for clear identification and verify this independently before making any purchase.

When choosing an individual octopus, try to select a younger specimen if possible. This gives you more time together before the animal reaches old age. However, you will also need to confirm the adult size of the species. Some octopuses grow far larger than a typical home aquarium can accommodate, so research maximum size before committing.

The legal and ethical aspects of octopus keeping deserve consideration. Sourcing animals through reputable dealers who can confirm collection methods helps avoid supporting unsustainable practices. Some keepers work with specialist marine aquarium societies to find captive bred specimens where available.

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Tank Requirements and Setup

Octopuses need a secure, well-maintained marine aquarium. They are notorious escape artists, capable of squeezing through gaps that seem far too small for their body size. Any opening in the tank lid, including filter outlets and cable holes, needs to be sealed or covered. A weighted lid is often necessary.

Water quality must be excellent. Octopuses are sensitive to ammonia, nitrite, and nitrate levels, and they produce a fair amount of waste. A mature tank with efficient filtration is essential. Most keepers recommend allowing the tank to cycle fully for several months before introducing an octopus. Protein skimmers are commonly used to help manage water quality.

Tank size depends on the species. Smaller species may manage in tanks of around 200 litres, while larger species will need significantly more space. Plenty of hiding places should be provided, as octopuses spend much of their time in dens or crevices. Live rock, clay pots, and PVC pipe sections all work well.

Temperature requirements vary between species, but most octopuses sold in the UK trade come from tropical or subtropical waters and will need heating to maintain stable conditions. Temperate species require a chiller, which adds to both cost and complexity.

Feeding and Day to Day Care

Octopuses are carnivores and need a diet of fresh or frozen seafood. Shrimp, crabs, mussels, and small fish are all suitable. Many keepers offer live food occasionally, as this provides enrichment and encourages natural hunting behaviour. Avoid feeding freshwater fish or processed human foods.

Feeding typically happens once a day or every other day, depending on the size and species. Overfeeding can quickly foul the water, so it is better to offer smaller portions and remove uneaten food promptly.

Octopuses are largely solitary and should be kept alone. They will eat most tank mates, including fish and invertebrates. Crabs and shrimp will be seen as food, not companions.

Regular water testing is part of the routine. Weekly partial water changes help maintain conditions, and you should monitor temperature, salinity, and nitrogen compounds consistently. Marine aquarium test kits are widely available from aquatic retailers.

For further guidance on keeping marine invertebrates, the British and Irish Association of Zoos and Aquariums (BIAZA) and specialist marine aquarium societies offer useful resources. Given the complexity of octopus care, consulting experienced keepers before purchasing is strongly recommended.

The Next Step

Now that you have read through the advice above, you might want to put it into practice. Our Aquarium Stocking Calculator lets you calculates safe fish stocking levels based on tank size, filtration, and species bioload. Try it now →