Warm-blooded animals habitually lives on land
while cold-blooded ones actually domiciles in water, one most important example,
is fish. It’s one of the most rudimentary
biology facts we’re taught in school growing up: Birds and mammals are
warm-blooded, while reptiles, amphibians and fish are cold-blooded. But newfangled
research is revolving this well-known knowledge on its head with the discovery
of the world’s first warm-blooded fish — the opah. This is really interesting!
Scientists already has
experimentally assumed that the opah was unusual, special and superior, says
Heidi Dewar, a researcher at NOAA’s Southwest Fisheries Science Center and one
of the paper’s authors. Most fish who live where the opah does — that is,
hundreds of feet deep, in some of the ocean’s shadiest and coolest places — are
lethargic, thanks to the low atmospheric condition with respect to moderate and
low temperatures.
At these lowest points, even
greedy and predatory fish tend to be slow-moving, waiting uncomplainingly for
prey to come by somewhat than actively chasing it down. But the opah, which
spends all its time in these deep places, has many features usually associated
with a quick-moving, active predator, such as a large heart, lots of muscle and
big eyes. These characteristics made the opah “a curiosity,” Dewar says.
Furthermore, in a paper
published today in Science, researchers from the National Oceanic and
Atmospheric Administration (NOAA) defines the unique device/mechanism that
allows and enable the opah, a deep-water predatory fish, to keep its body warm.
The secret lies in a specially designed set of blood vessels in the fish’s
gills, which allows the fish to circulate warm blood throughout its entire
body.
The opah’s secret chiefly
started to come out when NOAA researcher and lead author Nicholas Wegner observed
at a gill sample and perceived something fascinating and intriguing.
Virtually all fish have two varieties of blood
vessels in their gills: vessels carrying blood in from the body to pick up
oxygen, and other vessels carrying oxygenated blood back out again. In the
opah, the incoming blood is warm after circulating through the fish’s body.
This is because the opah swims by quickly flapping its pectoral fins, rather
than undulating its body like many other fish do, to propel itself through the
water — a process that generates high heat. But outgoing blood, which has just
been in contact with water in the gills, is cold. Wegner noticed that in the
opah’s gills, the two sets of vessels are tightly bundled against each other,
so that the incoming blood vessels can warm up the outgoing blood before it
goes anywhere else. This set-up, known as “counter-current heat exchange,”
allows warm blood to be delivered throughout the body.
Certainly, there are other categories of fish, such as tuna, which
have correspondingly designed blood vessels in certain parts of their bodies,
allowing for “provincial endothermy” — warm-bloodedness that’s limited to
certain organs or muscles, such as the eyes, liver or swimming muscles.
But the opah is the only
fish scientists know of that has this design in its gills, where most fish lose
the mainstream of their body heat to the surrounding cold water. By heating or
warming up the blood in the gills before it goes anywhere different, the opah achieves
not just regional endothermy, but whole-body endothermy. Puzzling and
experiment showed that the opah is clever and capable to maintain a body
temperature about 5 degrees Celsius warmer than the surrounding water.
Being warm-blooded gives
the opah a major competitive and modest advantage. Even fish with regional
endothermy usually can’t keep their heart warm. “If your heart’s cold, there’s
only so much you can do,” Dewar says. “It doesn’t matter how much your muscles
will perform, if your heart can’t deliver the oxygen and nutrients, your
muscles can only do so much.” This means fish like tuna must constantly make
trips back to the surface to warm up if they don’t want to slow down.
I strongly believe you should read this; [Why
a smallmouth bass with a rare, cancerous tumor has officials worried]
While only one species of
opah is currently recognized — according to Lampris guttatus — scientists are beginning
to conceive that they should actually divide the opah into several different
species based on genetic variations in diverse populations around the world,
according to Dewar. The opah in this study were found off the West Coast of
North America, so the next step will be to start sampling opah in other parts
of the world to see if they all have the same specialized gills, Dewar says
according to close studies from experiment conducted.
The opah, on the other
hand, can dedicate all its time in the deep waters without losing its advantage.
And being warm-blooded in such cold temperatures means its eyesight and muscle presentation
is piercing than its slothful nature, cold-blooded cousins. “The prey’s at a wide-ranging
disadvantage,” Dewar says.
Down the road, future
studies could also examine other related types of fish to try and figure out
how and when those exceptional gills grew and subsequently evolved. It’s conceivable
that other deep-water species have comparable and similar adaptations.
Meanwhile, all the same,
the opah relishes the spotlight as the world’s first — and, so far, only —
warm-blooded fish. “I think that it’s really thrilling, exciting and
electrifying that we spend so much time studying especially
these larger fish to find something that’s absolutely unique and has never been
seen before in any fish,” Dewar says. “We’ve been very excited about it.”
