October 19, 2021

I, Science

The science magazine of Imperial College

It may seem tiny, but this little baby will grow to one of the oceans' large and dangerous predatory fish.

baby swordfish

This week’s image is of the swashbuckling ‘Gladiator of the Sea’ – the swordfish, sometimes known as a broadbill. But this one’s a baby! Just 3 mm long and barely the width of a human finger, it will grow to be more than 39 inches by the end of its first year, and average around 10 feet.  Its eyes alone can grow to be bigger than  grapefruits, a size which baffled the internet when a swordfish eyeball washed up on a beach and went viral.

Swordfish have fascinating morphologies – although young swordfish have teeth and scales, these are shed as they grow older. They are ectothermic or cold-blooded, which normally means that the body produces no heat and must get it from external sources like the sun. Swordfish, however, are a rare kind of ectotherm as they have special organs in their heads which heat their eyes and brain, also improving their vision for when they catch prey.

And speaking of prey, the fish does indeed have a sword, not a spear. The bill is used to slash and injure prey, but not pierce or stab them. So while this brilliant blue baby may look cute, it will grow up to be one of the most dangerous fighters in the ocean, capable of nimble underwater runs, dashes, and leaps.

Naomi Stewart is studying for an MSc in Science Communication

Image: Jay Rooker, via Huffington Post