Space travel and the search for extraterrestrial beings is all well and good, but really, we have all the amazing and awe-inspiring alien-like lifeforms that anyone could possible dream up right here on Earth. Especially in the wet bits. I challenge anyone to watch the mind-bending documentary Fish Life – The Odd, The Weird and the Unusual and argue with that.

Take the mantis shrimp, a crustacean so specialised that it has its very own subclass (Hoplocarida). This ultra colourful creature grows to around 30cm, and is one beautiful beast, with possibly the most beguiling and brilliant eyes in the entire animal kingdom (it has three pupils in each eyeball, and can perceive 12 colour wave lengths, which is nine more than humans). But don’t be fooled by its lovely looks. This guy is like a psychopathic subaquatic cross between Predator, Inspector Gadget and the meanest MMA fighter you can imagine.

Let’s start with the two raptorial appendages on the front of this fighting machine, which can punch with the same velocity as a 22-caliber rifle, whacking opponents with 1,500 newtons of force within 3/1000 of a second. The shockwave created by its rapid-fire blows are enough to kill its prey even if it fails to land the punch properly, and the collapsing air bubbles generated by the movement create a burst of sonoluminescence. Pow!

With these weapons it’s capable of smashing open crabs, clams, oysters and tearing apart octopuses. It’s so strong, that the military has been studying the shrimp’s cell structure to see if it can be used in the development of body armour for frontline combat troops. Why haven’t you met this guy before? Because the mantis shrimp is so violent that most aquariums can’t keep them, without risking the murder of everything else in the tank. Oh, and because their punch is so powerful that it’s rumoured to be capable of smashing glass.

Shrimps, it transpires, are ruthless and intelligent killers (not to mention great dancers, you have to check out the gyrating moves of the thor shrimp, otherwise known as the sexy shrimp). Another species, the harlequin shrimp, is shown feeding in pairs—led by the far-bigger female and targeting starfish, helpless in their virtually stationary positions. The strong shrimps simply turn them over and eat them, stomachs first, concentrating on the parts that perish first.

Others, though, are a little less sociopathic. The film introduces us to one very odd couple, comprised of a shrimp and a gobi, who have a marriage of convenience. The industrious shrimp is constantly busy building a burrow for the two of them to live in while the gobi, which has much better eyesight but is rubbish at DIY, keeps a look out for danger.

And danger, it seems, lurks everywhere in this rough and tumble underworld full of streetwise wideboys. Take the boxer crab, a tiny but feisty little pugilist, who wears boxing gloves made from clumps of stinging anemones to swing at haymakers and his enemies. Not necessarily a tactic endorsed by the Marquess of Queensberry Rules, but pure genius nonetheless.

But it’s not all about underwater violence. This is really a documentary about the dandies of the depths, regardless of their ability to beat the bejaysus out of one another. We meet a kaleidoscopic spectrum of nudibranchs, for example, gastropod molluscs that come in a myriad of rainbow colours. These guys aren’t fighters, and since dispensing with shells they have developed an excellent method of self defence: they feed on toxic sponges and therefore become poisonous to most predators.

And then there’s the ephemerally eloquent sea pen, quill-like corals that capture nutrients from the water in their delicate feathers. One of my favourites, though, is dad-of-the-year contender, the mouthbrooding male jawfish. This guy might not be pretty, but he is completely selfless when it comes to his unborn kids (all 400 of them), forgoing food for eight days to keep the eggs safe in his mouth until they hatch.

It’s a weird and wonderful world down there, and this extraordinary film takes you on an astonishing tour of the strangest corners of it.

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Fish Life: The Odd, The Weird and the Unusual

With eyes, legs and mouths so radically different from our own human form, many underwater species could easily be mistaken as originating from another world. Witness the surprising and unusual physical adaptations that aquatic creatures have used with great effectiveness to survive for millions of years.