ATTENBOROUGH: Ours is truly a blue planet.
Water covers most of the world's surface.
Here, we are the outsiders.
But under the waves, one group thrives.
Fish.
Fish are masters of the waters.
And sailfish are the fastest of them all.
Their speed makes them one of the ocean's most fearsome predators.
Off the coast of Mexico,
30 sailfish have surrounded a ball of sardines.
To catch their prey requires more than speed alone.
In the tightest turns, fins maintain stability.
Their sickle-shaped tail powers them forwards
and that extraordinary dorsal fin helps intimidate their prey.
To the naked eye, the action is too fast.
Slowed, their challenge becomes clear.
Just picking a target is hard enough.
Knocking it off balance separates it from the shoal.
This requires extraordinary skill.
Not every attempt is successful.
But as more sailfish join in,
when one misses, another takes its place.
The shoal of sardines is methodically wiped out.
Sailfish are top predators, very little threatens them.
But for the majority of fish, this is not the case.
For most fish, the open ocean is extremely dangerous.
And some go to extraordinary lengths just to survive.
Flying fish.
Free of the water, they soar on elongated fins,
leaving their predators far behind.
A flight of fish.
Escaping predators is not the only test facing the flying fish.
They must also protect their developing young.
These flying fish are searching for the one thing
that will make this possible.
In such a vast ocean it's not easy.
They're in luck.
A palm frond.
It's a tiny island adrift in a huge ocean.
And like an island, it offers shelter,
not for the flying fish but for their eggs.
The females lay eggs on the raft, where the males fertilise them.
The first fish spawn and this triggers the others to start.
Soon, thousands join the melee.
Innumerable strands of eggs are laid.
The raft starts to tilt under their weight.
The best place to lay eggs is right inside the frond.
For some, the attempt proves fatal
and living fish become entombed.
The raft starts to sink under the weight of so many eggs.
But this is far from a disaster.
Sinking away from the surface
actually improves the eggs' chances of survival.
In just a few days,
having been safely hidden in the depths, they'll hatch out.
Other fish protect their offspring in different ways.
Some go to far greater lengths to care for them.
The shallow waters of southern Australia are home to many strange creatures.
It's a fairytale world of seahorses,
stargazers
and stingrays.
But none compare with the beauty of the weedy sea dragon.
The dragon's tiny fins beat frantically
to prevent the current from sweeping it away.
It's the beginning of spring,
the season when sea dragons begin their courtship.
And in the evening light, they start to dance.
In a graceful duet, each partner mirrors the actions of the other.
Darkness will soon draw a veil over the pair,
but they will dance on into the night.
Two months later and the result of their courtship is revealed.
It's the male
and he's the one that's carrying the eggs,
with rows and rows of them embedded in his tail.
That night, the female transferred her eggs to him.
Since then, the male alone has cared for them.
By carrying them with him, he's kept them safe.
And now it's time for his efforts to be rewarded.
The eggs are ready to hatch.
In the calm of a summer morning,
a baby sea dragon, with yolk sac still attached, is born.
The weed bed shelters older dragons
that are already able to feed themselves.
Although these dragons were well cared for by their father,
now they must find their own way in the world.
There are fish, however, which provide their young
with a safe refuge for far longer.
The Southwestern Pacific.
A convict fish, and it's something of a marine architect.
Underground, it has created a labyrinth of tunnels.
This adult never ventures out of its burrow.
What it eats is a mystery.
But it doesn't live here alone.
At another entrance, faces peer out.
Juvenile convict fish.
Unlike their parent, the youngsters are not tied to the burrow.
And as they start to emerge, a trickle becomes a flood of fish.
There are thousands of them.
And they all help with the chores.
Many hands make light work.
The young fish swarm together thousands of miles, gulping plankton.
What the adults eat must somehow involve these youngsters.
Whether the young feed their parents by regurgitating food
or through some other mechanism, we just don't know.
Whatever the answer, the youngsters provide their parents with a meal
and in return, get a roof over their heads.
Producing young is just one challenge.
Finding food and somewhere to live are further trials fish must face.
The Californian coast. A wide range of species live here.
But all this life means competition for living space is intense.
Old shells are highly prized.
And this one is occupied by a sarcastic fringehead.
These fish are exceptionally quarrelsome.
They have to be to defend their living space.
An octopus.
Inadvertently, it's wandered into the fringehead's territory
and that can't be tolerated.
The octopus' impressive jab holds the fringehead at bay.
There is more to this behaviour than being bad-tempered.
The fringehead needs to defend its patch if it is to get enough to eat
and the octopus was competition.
Crabs are not the easiest of mouthfuls.
Because of the shortage of living space, there are constant boundary disputes,
especially with other fringeheads.
And this one has got too close.
Despite the most extravagant threats,
neither is prepared to back down.
Success. And it's quick to get back to its shell.
A fringehead can never drop its guard, there's too much competition.
Some fish have moved to places where they have fewer rivals.
A mudskipper, a fish that spends most of its life out of the sea.
It can walk on land and breathe air.
Its life is very different from that of most fish.
A fish out of water, maybe.
But they thrive here in Japan.
So what's made this upheaval worthwhile?
The answer lies in the mud.
As the tide retreats, it exposes mudflats.
Sunlight hits the rich silt
and tiny plants and animals flourish there.
All food for a mudskipper.
(CROAKS)
But life on land is not without problems.
It's hard work to find a mate.
Jumping high above the mud will get you noticed.
With eyes perched on the top of their heads,
the mudskippers keep a lookout for both friend and foe.
And males fight those who intrude on their territory.
They must also take care not to dry out in the sun.
Rolling in the ooze keeps the skin cool and moist.
For this smaller species,
a better option is to retreat underground.
So he digs himself a tunnel down into the mud.
His heap of spoil is an indication of the extent of his excavations.
With the tide flooding the tunnel twice a day,
maintenance is a real burden.
The tunnel is more than a refuge from the sun.
It serves another very important purpose.
The tunnel is actually U-shaped.
And at the far end is a sealed chamber,
the walls of which are lined with eggs.
The eggs are kept in air, as it's richer in oxygen than the water.
The problem is the air that's trapped here won't last for long.
So the male travels to the open end of the tunnel to gulp fresh air.
Back he goes down his tunnel, where he releases it into the egg chamber,
replenishing the oxygen on which the eggs depend.
He will repeat this hundreds and hundreds of times,
until his young hatch.
This lifestyle is very demanding,
yet the mudskipper has found a way around every problem.
The harsh challenges of life in the ocean
have encouraged other fish to leave the sea.
Not for land, but for fresh water.
Hawaii is the remotest island chain on the planet.
These pools look the perfect place for a fish to live,
secluded and free from competition and predators.
Yet few contain fish, for one very considerable reason.
Surely no fish could swim up this.
But one fish comes from the ocean intent on colonising these streams.
It's a tiny goby and it's a rock climber.
With pelvic fins fused into a disk which acts like a sucker,
all the goby needs is a film of water to climb through.
The pioneer is soon followed by many others,
possibly following its scent trail.
They clamber on, ever upwards against the flow.
Drops of water fall like bombs.
False leads waste crucial energy.
Some must rest.
For others, the effort is just too much.
Many die in their attempt to reach the top.
Against all the odds,
a few heroic individuals do make it to the top.
They find themselves in a near perfect fish habitat,
where the gobies can feed and grow and breed in peace.
In time, their own young will be swept downstream and out to sea
and the cycle will begin all over again.
Fresh water presents particular challenges for fish.
Nutrients can be in very short supply in spring water,
so here, fish must take every chance they can to find food.
The rain that falls on these Kenyan hills
percolates through the rocks,
finally emerging as crystal-clear pools...
pools that are home to fish including barbel.
The fish share these waters with all sorts of creatures...
including hippopotamus.
(GRUNTING)
These giant vegetarians are no threat to the fish.
In fact, they're key to their survival here.
After a night of grazing on land,
these hippos return to spend the daylight hours in the cooling waters.
And the barbel come to meet them.
Soon, each hippo is trailed by a shoal of fish
waiting for their breakfast,
hippo droppings.
But it's not just the hippo's dung the fish are interested in.
When the hippos reach one particular spot in the pool,
they stand still and wait.
And the fish start to clean them,
removing ticks, parasites and other tasty morsels.
To the fish, the hippos are a mobile cafeteria.
The hippos seem to be enjoying the sensation.
The only thing that interrupts the feast
is the need to take an occasional breath.
Cleaning the hippo's skin was just the hors d'oeuvre.
Now it's time for the main course.
So in addition to providing skin care,
the fish look after the hippo's dental hygiene.
It's an arrangement that suits both parties.
But perhaps it's the fish that are the overall winners.
For thanks to the hippos, they are able to feed on the abundant vegetation
that would otherwise be beyond their reach,
growing around their pool on land.
Providing a cleaning service is clearly a good way of getting a meal.
And there is cleaning to be done in the sea as well.
The life of this wrasse is centred on removing parasites from other reef fish,
including predatory Jacks.
Normally, they would snap up such a little fish,
but this is an established relationship and both sides know the rules.
With so many Jacks and only a few wrasse in attendance,
not all the Jacks are going to get cleaned.
But all this life attracts other predators.
Silvertip sharks.
The reef provides shelter for the smaller fish,
but the Jacks remain exposed.
Yet this may be a chance for the Jacks to solve their cleaning problem.
They've spotted an opportunity.
Sharks have skin like sandpaper.
And bumping into the sharks' flanks
helps the Jacks to rid themselves of parasites and dead skin.
Perhaps the Jacks find this a more effective alternative
to the cleaner fish.
And soon swarms of Jacks pursue the sharks,
all itching to have a scratch.
Unsurprisingly, all this attention bothers the sharks
and they head back to the blue water,
leaving the residents of the reef to resume life as normal.
Coral reefs are the richest habitats on Earth.
It's not surprising that with so many different kinds of animals
living so closely together,
some extraordinary relationships have evolved.
The clownfish, a small and defenceless resident of the reef.
It seems to have picked a tough place to live,
amongst the tentacles of the sea anemone.
Each tentacle is armed with paralysing stings that can kill a fish.
Yet the clownfish are totally immune.
For this pair, the anemone is like a castle.
So long as they stay surrounded by the tentacles, they're safe.
And so this is where they choose to lay their eggs.
After carefully selecting the site, work begins on preparing the surface.
Both fish share in the labour,
though it's the larger female who decides when all is ready.
Lines and lines of tiny eggs are stuck to the rock and then fertilised.
They're laid so close to the anemone, they will be safe.
And for the next seven days, they'll receive constant care,
much of which is provided by the male.
His seemingly obsessive concern for the eggs is for good reason.
His position in the anemone is far from secure.
The female watches his every move.
She's in charge here
and if his efforts don't match up to her standards, she'll get rid of him.
In line to take over are a host of immature clownfish,
each waiting to move up the hierarchy.
For the male, the best way to stay in the female's favour
is by lavishing care on the eggs.
So he focuses all his efforts on keeping them clean and healthy.
The eggs grow rapidly and soon their tiny beating hearts are visible.
It seems he's done a good job.
Clownfish can hide away within an anemone.
But most fish don't have this option.
For some, the only way of avoiding danger
is by hiding amongst their own kind,
in shoals.
Packed close together, no one anchovy stands out.
By sensing and reacting to the movements of their immediate neighbours,
thousands can move as one.
For a predator, picking out an individual becomes nearly impossible.
The shoal's unity is its strength.
Yet each fish is acting from selfish motives.
Moving together, the fish confuse the sea lions so much
that they leave to look elsewhere for a smaller, less tricky target.
The sheer size of the shoal defeated the sea lions,
but there are fish that can overcome such strategies.
Off the coast of South Africa,
this huge shoal of sardines is shadowed by a ragged-tooth shark.
Other sharks join the menacing escort.
The shoal has been driven into the shallows by a cold ocean current
and this gives the sharks an opportunity.
Hundreds have moved into position.
Sharks have a special sense.
They can detect the electrical signals their prey gives off when it moves.
It's a sixth sense that can give them an edge.
But with hundreds of thousands of fish crammed into the shallows,
the sharks need only rely on their speed and agility.
As the first shark starts to hunt in earnest,
a feeding frenzy breaks out.
The shoal's defences are weakened.
There isn't enough space to manoeuvre.
And the sharks can gorge themselves.
Despite the casualties, the shoal is so vast
that the sharks have little effect on its size.
Fish not only come together in great shoals for defence,
but at other critical times in their lives
when they're ready to spawn.
These events only occur for a few days each year.
Snapper are normally solitary,
but they've travelled here from hundreds of miles away
to gather off the coast of Belize.
Along this one reef, cubera, dog and mutton snapper form huge shoals.
60 metres down, there is an eerie coolness to the scene.
But things are about to hot up.
It's the evening of the full moon, the tides are just right.
A great column of fish leaves the bottom.
As they rise through the water, small groups break free of the shoal.
Each burst is led by a female with the males racing behind.
As she sheds her eggs, they add their sperm to the mix.
By synchronising the time when they gather together,
the maximum numbers of fish can join in this mass spawning.
Millions of fertilised eggs are released, cast into the ocean currents
and straight into a dangerous world.
Whale sharks, the largest fish on Earth.
Each shark might weigh 10 tons,
yet they feed on the tiniest creatures, including snapper eggs.
Life is being created, sustained and destroyed simultaneously
in one huge event.
The struggle for life encapsulated into a single moment.
The oceans are perilous places to live,
yet fish have developed the most extraordinary means for survival.
Their astounding diversity,
the product of millions of years of evolution,
has enabled them to triumph,
dominating the one habitat
that we have so far failed to make our own.
Filming underwater raised all sorts of problems for the Life team,
not least of which was that they were only able
to experience the underwater world
for as long as the air on their backs or in their lungs held out.
But over three years, the team were lucky enough to capture on film
some extraordinary moments in the lives of fish.
The waters off the Yucatan Peninsula in Mexico
are a rich hunting ground for sailfish.
Cameraman Rick Rosenthal
has teamed up with sport fishing captain Anthony Mendillo
to try and film the hunting behaviour of these amazing animals.
MENDILLO: It's fish.
ATTENBOROUGH: Feeding birds lead them to the sailfish.
- Right here. - Right here.
Getting to the bait balls and into the water quickly is key
before the feast is consumed.
MENDILLO: Get ready.
Or they're gonna eat it, then we'll be screwed.
Everybody hang on.
They're out there swimming now, now.
Come on, get in there.
It's all very well telling Rick to hurry,
but these fish are capable of swimming at over 60 miles an hour.
Just keeping up with them is hard enough.
Getting right in amongst the action is vital,
but Rick has to try to avoid becoming part of it.
Bills nearly one metre long,
scything through the water at breakneck speed,
are guaranteed to get the heart racing.
But Rick holds his nerve
as the sailfish pick off sardine after sardine right in front of him.
Almost as soon as it started, it was all over.
Had a wild sea show out there today. Really wild.
Must have been 50 sailfish if there were 49.
But very aggressive fish, very hungry, everybody on the move.
And I had to just keep kicking and kicking and kicking
and kicking and kicking and kicking to keep in the action.
But after a while the sardine patch was eaten up to just a little sliver.
And then it was over.
ATTENBOROUGH: Nearly 2,000 miles away on the other side of the Caribbean,
another crew is taking a slightly different approach.
They are trying to film flying fish.
The team sets out at dawn on the Hog Snapper, a commercial fishing boat.
Conditions are in stark contrast to the gleaming sport fishing boat in Mexico.
There's Doug, he's ready for action. Look.
What's up?
ATTENBOROUGH: They are hoping to use a local fisherman's expertise
to put them in the right place at the right time.
Yeah, roger that. Yeah, roger that.
Oh, you catching today's food.
You catching dinner, lunch and breakfast, you know.
MAN: (OVER RADIO) Roger.
ATTENBOROUGH: It's not a big boat
and the crew's bedroom has now become the kitchen.
We're having fried bacon, fried egg this morning.
Fried bacon, fried eggs.
(LAUGHING)
I'm the trainee chef, so I don't get to wear the white wellies.
(ALL LAUGHING)
ATTENBOROUGH: Rather than racing around the ocean chasing the action,
the flying fish team have to sit it out and wait for the fish to come to them.
Flying fish will spawn onto debris in the water.
And the team tie onto a floating palm frond
to try and make sure they're close by in case the action begins.
And sure enough, they don't have long to wait.
Thousands of fish have massed below the surface,
all intent on reaching the frond.
And the frond is not the only thing
that they're trying to lay their eggs on.
The weight of the eggs sinks the palm frond
and puts an end to the spawning and to the crew's filming.
Well, it's moments like that we do the job for.
Everything was right. The light was right, blue water,
the four tons of flying fish all going mental.
- Thanks, Barry. - You're welcome.
ATTENBOROUGH: But now the fishes' attention is turned to something bigger.
They're spawning directly onto the boat.
Barry is worried as he drags up a huge sheet of eggs.
Want to bring it in the boat and check it out? I cleaned this off
like five minutes ago, right?
Right now the problem is that there are too many flying fish around us.
If we go through the night with the lights on and stuff,
more and more and more will keep coming
and what they're doing here is they're actually laying on the boat now.
So the boat has become their object and that is not good.
So basically you're worried that if we just stay on this drift,
we're gonna sink the boat.
Five hours from now, that will be 3,000 pounds, yeah,
in the back here, it will sink the boat.
- Okay, so we're going to leave. - Yeah, we can't stay here.
ATTENBOROUGH: Just five minutes of spawning has produced this.
The team have no option but to move on.
The next day, the search for flying fish begins all over again.
This time the team want to film the fish doing what they're famous for.
We've got some lovely shots of them spawning
but now the really hard bit of trying to get them flying.
It's gonna be a good challenge.
ATTENBOROUGH: The fish are around, but they're all too far off to film.
The action is impressive this morning.
Unpredictable but impressive, but it's distant.
And it's not happening next to the boat today.
They're either being chased off by something or they're just not inter...
Look, look, look. It flies!
Ay-yi-yi!
ATTENBOROUGH: The next day, the crew decides
to try a different approach.
Cool.
All right, let's go.
Now they're just where they need to be,
but it puts them directly in the firing line.
(LAUGHING) I guess that's one.
Despite being bombarded, their strategy is paying off.
That was amazing. We spent a long time in that wee boat today. Thanks.
The last two hours were just off the scale,
we were just getting shot after shot.
We need... Can't wait to watch on the big monitor, but that felt really good.
ATTENBOROUGH: And Doug is right. It worked.
Flying fish taking to the air and flying,
slowed down 40 times.
By working with people more used to catching fish than filming them,
the Life team have been able to gain a unique insight
into the hidden world of fish.