Aquariums are not just about fish. Just like the deep blue sea itself, your tank may feature a range of other organisms, from simple plankton to more substantial creatures such as anemones and molluscs.

In the latter case, octopuses are among the most fascinating of creatures. Like many fish, some end up on a dinner plate, but these are wonderful and sometimes surprisingly intelligent animals that make great pets.

Telling them apart from squid is rather like knowing the difference between hares and rabbits, or frogs and toads. As the name suggests, octopuses have eight tentacles, while squid have eight arms plus two long tentacles and find on the side. Octopuses have bulbous heads while squid have elongated bodies, and only squids can fire ink to hide themselves from predators.

A significant difference is intelligence. Octopuses are believed to be the smartest invertebrates of all. They can display personality, change colours in fascinating ways, and can even use tools. However, it is debatable whether they really can forecast football results.

Some aspects of keeping an octopus are easy and you’ll need just a few marine accessories. Because they don’t mind the dark and love to hide, you won’t need lots of bright UV lights and they only need simple wet-dry filtration. Unless you buy a species that grows very large, you won’t need a huge aquarium. You need to maintain a salinity of 1.022-1.023 and a PH of 8.2 in most cases.

The main challenge is they can cost a lot to feed, as they have big appetites and they need lots of the right stuff, such as crustaceans. They will accept thawed shrimp, but will want some live food such as crabs. In addition, the fact they are big eaters means you can’t keep them in the same tank as other fish, as they will soon be eaten.

Sadly, one drawback is that octopuses only live around a year each. Apart from the great loss to football punditry, this also means that, wonderful and fascinating as these creatures are, you should avoid getting too attached to them.