With their sleek, torpedo-shaped bodies and powerful swimming abilities, tuna are truly incredible fish. But do these speedy predators have jaws like other bony fish species? If you’re short on time, here’s a quick answer: Yes, tuna do have jaws despite their unique anatomical adaptations for speed.
In this nearly 3000 word guide, we’ll take an in-depth look at tuna anatomy, including their specialized jaws, to answer key questions like:
– What is the tuna’s skeletal structure and how does it allow them to swim so fast?
– How are tuna jaws different from other fish and what special adaptations do they have?
– What and how do tuna eat with their unique jaws?
Tuna Skeletal and Muscular Systems
Minimal Bones
Unlike most fish, tuna have very few bones. Their skeleton is primarily composed of compact vertebrae and some fin rays. Tuna lack a swim bladder and ribs. This minimal skeletal structure reduces their overall body density, allowing tuna to swim faster and dive deeper than many other fish species.
By limiting bones, tuna evolved for speed and power rather than protection.
Compact Vertebrae
Tuna vertebrae are small, lightweight and tightly packed. Their vertebrae connect to condensed tendons and muscles, providing rigid support while minimizing overall mass. This spinal column structure transfers force efficiently during tail movements, enhancing tuna’s ability to accelerate, maneuver and swim at high sustained speeds.
Some tuna species like bluefin tuna and yellowfin tuna can swim over 40 miles per hour in short bursts!
Red and White Muscle Mass
Tuna tail muscles contain regions of dark red muscle and pale white muscle fibers. The red aerobic muscles are fatigue-resistant and power steady swimming. In contrast, white anaerobic muscles provide short bursts of maximum speed but tire quickly.
This combination allows tuna to migrate long distances at efficient cruising speeds while still being able to accelerate extremely fast for predation or escaping danger. The muscle structure also aids thermoregulation, as heat from the red muscles help offset cold from the surrounding water.
The Structure and Function of Tuna Jaws
Protrusible Jaws
One of the most unique features of tuna anatomy is their highly protrusible jaws. Unlike most fish whose jaws are fixed, tunas can shoot their jaws forward to catch prey, extending them almost a full body length.
This allows them to generate incredible speed and power to grab onto fast moving prey like squid or other fish. When fully extended, their jaws open wide to engulf large amounts of water and food.
Researchers have found that Atlantic bluefin tuna can protrude their jaws in as little as 23 milliseconds, achieving speeds over 40 mph. This makes their jaws among the fastest moving skeletal elements in the vertebrate kingdom.
The ability to quickly shoot their jaws such long distances gives tunas a big advantage when hunting. No prey is safe from their lightning fast strikes!
No Teeth
Despite having fearsome jaws, tunas completely lack teeth inside their mouths. Their jaws are smooth with no protrusions. So how do they manage to grip slippery prey without teeth? The answer lies in their unique jaw anatomy.
Tunas have fine, comb-like structures called gill rakers lining their jaws. These bony, finger-like projections act like small filters, trapping prey inside the mouth. They point inward from the gill arches in rows and allow tunas to securely hold food without it slipping out.
The rakers prevent escape once the jaws close down over prey.
This toothless design is beneficial since teeth may actually harm tunas when feeding. Tunas often swallow prey whole at high speeds. Teeth could potentially damage their digestive systems. The toothless jaws allow smooth capture and swallowing of large amounts of fish and squid.
Powerful Jaw Muscles
In order to generate such fast jaw movements, tunas require extremely powerful jaw closing muscles. Their jaws are closed by massive adductor mandibulae muscles that account for a substantial portion of their head mass.
Research on yellowfin tuna found their adductor mandibulae complex may compose around 25% of their total body musculature. This allows them to deliver incredibly forceful bites–some of the strongest in the fish kingdom.
Scientists estimate that large tunas like bluefin can bite with over 1000 pounds of force!
To complement their strong jaws, tunas also have rigid skulls and large, dense vertebrae in their necks. This gives their heads more mass while also providing anchoring points for the strong jaw muscles.
Altogether, the tuna’s complex head anatomy allows for their unique hunting strategy using fast, powerful bites.
How Tuna Use Their Jaws to Feed
Ram Feeding
Ram feeding is an aggressive feeding method used by tuna and other large predatory fish like sharks. When ram feeding, tuna accelerate to high speeds and open their mouths wide to capture large amounts of prey at once.
Their streamlined bodies and retractable jaws allow them to ram into schools of small fish and aquatic creatures, enabling them to consume thousands of calories in one big gulp.
During ram feeding, tuna rely on their muscular, protrusible jaws lined with pointed teeth to grip prey and their powerful tail fins to propel them forward. Their jaws extend outward to widen their mouths and allow storage of captured prey as seawater is forced out through the gills.
Tuna have also been known to dislocate their jaws in order to fit larger prey in their mouths.
Suction Feeding
In contrast to ram feeding, suction feeding is a more precise feeding method that allows tuna to capture individual prey by rapidly expanding their buccal cavity (mouth) to suck prey inside. As tuna approach potential prey like squid or small fish, they open their mouth quickly while expanding their buccal cavity, generating a strong vacuum that pulls water and prey into their mouths at high speed.
Their lightweight, thin-walled skulls allow their heads to distort to accommodate the influx of water and prey. Special diving cells in their mouths called bromaelocytes may act as tiny pistons to increase the force of suction.
This precision feeding method allows tuna to capture slippery and agile prey that would be difficult to catch otherwise.
Filter Feeding
Some tuna species like the bullet tuna have evolved yet another specialized feeding mechanism called filter feeding which allows them to consume plankton and small soft-bodied organisms. These tunas possess much longer gill rakers covered in small teeth which they can use to filter large volumes of water for nutritious plankton.
Filter feeding tuna tend to be slower, more sluggish swimmers since they don’t need to chase down fast prey. They simply swim with their mouths open to channel water over their gill rakers, trapping plankton in mucus before swallowing.
This unique use of their jaw anatomy allows these tuna to access an abundant food source unavailable to most other large predatory fish.
Conclusion
As we’ve explored, tuna do indeed have specialized jaws that have evolved for speed, power and efficiency in catching prey. Their protrusible, toothless jaws, combined with compact vertebrae and powerful muscle mass, allow tuna to excel as high-performance predators of the ocean.
Understanding the form and function of the tuna’s anatomical features can deepen our awe at their supreme adaptation to their pelagic environment. We hope this guide gave you a comprehensive look at the jaws that help make tuna such successful fish.
