Weird fish of the week: Opah

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The enigmatic Opah (Lampris guttatus) is certainly an ocean oddity, but it is surely also one of the most beautiful fish to be found in the world's seas.

It can be hard to pinpoint just what it is that makes a fish weird. Fish are incredibly varied creatures and are adapted to almost all the watery habitats the world has to offer and this vast range of conditions is the anvil on which their shape and behaviour has been forged.

We all have a basic image of what a fish 'should' look like - fish shaped as it were - but even in a world of seemingly infinite variation some fish stand out from the crowd.

This week's weird fish candidate – the Opah – is a marine mystery, a huge fish that almost nothing is known about.

These mighty marine travellers grow to 2m/79" long and being almost circular in profile their body can be nearly as deep, at which size they can top 250kg/550lb.

This huge disc-like body is a wonderful steely blue colour along the dorsal surface, fading through purple, green and silver to a rosy pink on the belly and the whole fish is covered in silvery spots, giving the impression of a starry night's sky fading at dawn.

If this alone isn't beauty enough, then the Opah's fins are a magnificent fiery scarlet and its eyes a lustrous gold.

The only encounters recorded with these mysterious fish are from fishermen, for whom the species is a prized catch, or from the occasional strandings of dead or dying specimens.

They are thought to be restless, lone travellers ceaselessly swimming throughout the world's oceans where they are known to dive to depths in excess of 400m in search of their favoured prey of squid.

Recent research has shown they have evolved special adaptations to deal with the sudden temperature drops this can cause. It is believed the rapid cooling associated with deep diving can cause problems with brain function and sight so they have developed special layers of muscle around the brain and behind the eyes capable of maintaining these vital organs at up to 6°C higher than the rest of the body, an adaptation known as cranial endothermy.

They propel themselves mainly with wing-like flapping of their pectoral fins and clearly can achieve considerable speed as they are often found in the company of sea-going speedsters like Tuna.

This combination of size and speed mean that once adult their predators are limited to fast moving shark species such as Mako and Great white.

There is only one other species in the Lampridae family, the smaller Southern Opah, Lampris immaculatus which as its name suggests is found only in the southern oceans and grows to around 1m/39".

Why not take a look at some of our other Weird fish of the week features?

Barreleye 

Mega mouth shark

Flying gurnard

Pinecone fish

Slender snipe eel

Tripod fish

Lumpsucker

Ocean sunfish

Two-headed arowana

Stargazers

Giant oarfish

Kroyer's deep sea anglerfish

Halimeda ghost pipefish

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