The secret lives of baby fish - Amy McDermott

What you're looking at isn't some weird x-ray.

It's actually a baby yellow tang surgeonfish at two months old.

And you thought your childhood was awkward.

But here is the same fish as an adult,

a beautiful inhabitant of the Indian and Pacific Oceans' coral reefs

and one of the most popular captive fish for salt water aquariums.

Of the 27,000 known fish species, over a quarter live on coral reefs

that make up less than 1% of the Earth's surface.

But prior to settling down in this diverse tropical environment,

baby coral reef fish face the difficult process of growing up on their own,

undergoing drastic changes, and the journey of a lifetime

before they find that reef to call home.

The life cycle for most of these fish

begins when their parents spew sperm and eggs into the water column.

This can happen daily, seasonally, or yearly depending on the species,

generally following lunar or seasonal tidal patterns.

Left to their fate, the fertilized eggs drift with the currents,

and millions of baby larvae hatch into the world.

When they first emerge, the larvae are tiny and vulnerable.

Some don't even have gills yet and must absorb oxygen

directly from the water through their tissue-thin skin.

They may float in the water column anywhere from minutes to months,

sometimes drifting thousands of miles across vast oceans,

far from the reefs where they were born.

Along the way, they must successfully avoid predators,

obtain food, and ride the right currents to find their way to a suitable adult habitat,

which might as well be a needle in vast haystack of ocean.

So, how did they accomplish this feat?

Until recently, marine biologists thought of larval fish as largely passive drifters,

dispersed by ocean currents to distant locales.

But in the last 20 years, new research has suggested

that larvae may not be as helpless as they seem,

and are capable of taking their fate in their own fins

to maximize their chances of survival.

The larvae of many species are unexpectedly strong swimmers,

and can move vertically in the water column to place themselves in different water masses

and preferentially ride certain currents.

These fish may be choosing the best routes to their eventual homes.

When searching for these homes,

evidence suggests that larvae navigate via a complex suite of sensory systems,

detecting both sound and smell.

Odor, in particular, allows larvae to distinguish between different environments,

even adjacent reefs,

helping guide them toward their preferred adult habitats.

Many will head for far-flung locales miles away from their birth place.

But some will use smell and other sensory cues

to navigate back to the reefs where they were born,

even if they remain in the larval stage for months.

So, what happens when larvae do find a suitable coral reef?

Do they risk it all in one jump from the water column,

hoping to land in exactly the right spot to settle down

and metamorphose into adults?

Not exactly.

Instead, larvae appear to have more of a bungee system.

Larvae will drop down in the water column to check out a reef below.

If conditions aren't right, they can jump back up

into higher water masses and ride on,

chancing that the next reef they find will be a better fit.

But this is the point where our knowledge ends.

We don't know the geographic movements of individual larva for most species.

Nor do we know which exact environmental cues and behaviors they use

to navigate to the reefs they will call home.

But we do know that these tiny trekkers

are more than the fragile and helpless creatures

science once believed them to be.

The secret lives of baby fish remain largely mysterious to us,

unknown adventures waiting to be told.