Jan. 25, 2008 -- The great barracuda deserves its fearsome reputation, suggests a new study on its predatory ways. The toothy fish tackles large prey, the study's authors report, by impaling its victim with sharp fangs and then slicing it in half, scissor-style.
The technique may explain why barracuda stomachs are often found to hold multiple "back-halves" of prey, since the force of the event often sends the front halves flying out of the barracuda's mouth.
"The barracuda is a lightning-fast predator," said Aaron Rice, a co-author of the study and a postdoctoral fellow in the Department of Neurobiology and Behavior at Cornell University.
"In literally thousandths of a second, once a prey fish is located, the barracuda performs a giant tail-beat to accelerate forward while the jaws are opening, then impacts with the prey fish moments later, closing the jaws on contact," Rice explained.
To determine what barracudas do next, Rice and colleagues Justin Grubich and Mark Westneat studied the anatomy of seven great barracudas across a large range of body sizes. They also captured barracuda biting with high-speed video that revealed the process frame by frame.
The findings are published in the current issue of Zoology.
Their conclusion? A barracuda bite is "like a combination between scissors and a steak knife," said Rice.
"Barracuda jaws work similar to scissors in that there are two opposable sharp edges, which quickly close and cut the food item from the top and bottom," he explained.
The tropical predator's teeth are unique among all other fishes, sharks, reptiles and mammals. In addition to having teeth embedded in the upper and lower jaws, barracudas have additional teeth on two sets of bone, called the palatine, inside its mouth.
The extra teeth allow the upper jaw to be used for grasping prey, while the lower jaw and palatine teeth do the actual cutting. Prominent, fang-like teeth protrude from the front of the upper and lower jaws, helping with impaling and grasping.
Rice and his team noted that sometimes barracudas "would literally spear the prey fish on those giant fang-like teeth in the front, and there were other strikes where the barracuda would be able to seize the prey fish with the middle or back of the mouth, and then close its jaws."
The total force of the barracuda's strike is 720 Newton, with most of that force concentrated along a very small area of the fish's tooth tips. By contrast, spiny dogfish sharks only have a bite force of 20 N.
There have been numerous reports of barracuda attacks on humans, resulting in limb amputations or, rarely, death. Rice said barracudas are not overtly aggressive or desirous of humans, unless the person is wearing a bright, reflective object, such as a metallic watch or a diving knife. Nevertheless, he advised to swim clear of the toothy fish if one is spotted.
Philip Motta, a professor of biology at the University of South Florida, is now investigating the muscles that barracudas use when they attack. Motta's team specializes in the anatomy and mechanics of fish feeding.
The new paper represents "an exciting and interesting investigation into the feeding biology of this fascinating predator," Motta said.
Despite all of the research on barracudas, Rice said that "we have only scratched the surface in terms of understanding how barracuda feed." He hopes his work "will inspire others to investigate how these incredible fish function and what makes them so special."
Related Links:
Jennifer Viegas' blog: Born Animal