Cornetfish

Image: Rob

A sliver of fish cuts through the tropical darkness like a silver blade, a defiant icicle, or a really long pencil sharpened at both ends.

I'd have thought it was an innovation in mermaid warfare: a javelin drone. Throw it and it swims into enemy territory under its own steam, using those massive eyes to seek out ne'er do wells where'er he dwells. But no, turns out it's a musical-instrumentfish sharpened at both ends. Don't mess with mermaids, man, even their orchestras are ready for battle.

Image: jome jome
Bluespotted Cornetfish (Fistularia commersonii)

Whether you're a music lover, a mighty warrior or something in between, it's important to note one thing: Syngnathiformes are weird. They're the "fused-jaw" fish like the Seahorse, with its horribly twisted body kept in mangled shape by bony plates of unyielding armour. Or the Pipefish, which is basically a Seahorse stretched out into a more reasonable shape.

Now it's time to take a look at the Pipefish's big brother, the Cornetfish.

Image: Bryant Kevin
Fistularia tabacaria, even more blue-spotted than the Bluespotted Cornetfish

A cornet is a kind of brass instrument, like a trumpet but more bunched up and compact. It's basically a pipe, twisted and bent into something that would make even a Seahorse wince. Which is odd because Cornetfish aren't twisted or bent out of shape at all. Maybe Oboefish would have been more accurate?

There are only four species of Cornetfish, together found all over the world in tropical and subtropical waters. They all belong to the genus Fistularia which is the only genus in the family Fistuliidae. Fistularia means 'flute' and indeed Cornetfish are also known as Flutemouths. I guess they do look like they're about to play the flute, just remember that the woodwind section is also ready for battle.

Image: Nemo's great uncle
Red Cornetfish (F. petimba). Not always red

The biggest of all the Cornetfish is also probably the most widespread. The Red Cornetfish can be found from Japan to Australia, East Africa and the Red Sea to Hawaii, the Mediterranean and even Florida down to Brazil.

A really big individual can reach up to 2 metres (6.5 feet) long, though a more typical length is more like 180 cm (6 ft). Either way, that's getting into Bassoonfish territory.

Image: Kahunapule Michael Johnson
Pacific Cornetfish (F. corneta)

On the other side of the scale, the smallest is definitely the least widespread. Almost as if it lost the fight when the Cornetfish were carving up the world between them. The Pacific Cornetfish attains a mere 20 cm (7.8 in) on average, though apparently, some individuals can reach a metre (40 in) long (I don't know what kind of growth pills that guy was taking!).

They live in the areas the Red Cornetfish left over, the other side of the Americas, from California down to Peru.

Image: Derek Keats

So it looks like size matters when it comes to Cornetfish. Length, to be more specific. They're very one dimensional that way. Or... two dimensional.

They clearly have a long and slender body, but their head is so long it takes up almost a quarter of their total length! Then, just to eke out a few more inches, their tail ends in a long filament.

Video: Germano NZ

They can really enjoy that length, too. Unlike Seahorses and Pipefish, Cornetfish are mostly liberated from the tough, bony armour common among the Syngnathiformes order. The Bluespotted Cornetfish has a row of bony plates running along its back but it's not enough to stop it flexing and curving when it wants to. What, after all, is the point in being that long if you can't see your own tail?

Cornetfish spend most of their time swimming slowly in shallow waters, over coral reefs, sandy plains or rocky rubble. They're surprisingly smart about hiding. The Red Cornetfish can hide behind fatter-bodied fish or swim vertically among plants.

Video: DiveNowGuru

They can even change colour! Acquiring some dark stripes lets them hide among rocks and seaweed.

They also have a very well-developed lateral line. Do you remember the lateral line? It's like an ear stretched out over the entire length of a fish's body, with lots of tiny hairs for sensing (hearing) vibrations in the water. In Cornetfish, this lateral line extends all the way down into that long tail filament. It's almost like an antenna!

Image: John Turnbull

And don't go thinking Cornetfish are some kind of shrinking violet or limping posy or generally fearful flower. These guys are predators. A thrash of the tail and they jump into action or burst out of their hiding place to chase down small fish, squid or shrimp. Then they open that tiny mouth at the end of their long tube-snout and hoover up their dinner.

To be honest, the more I learn about Cornetfish the more it sounds like an amazing innovation in mermaid warfare. It's a ninja javelin drone that can hide behind local fauna or disappear in the bushes. It can covertly listen in on conversations and if it gets caught, it can pretend to be an itinerant flautist. Genius!