Great barracudas live in warm seas around the world, around coral reefs, seagrass beds and mangroves. They prefer water between 74 and 82 degrees Fahrenheit, though they have been found in much colder water. A great barracuda hunts by ambush and finds its prey mostly by sight.

Barracudas use a feeding style that the Field Museum scientists named 'ram-biting': a ram strike followed by biting with a scissor-like motion of the jaws. A great barracuda closes its jaws only after the prey is already inside its mouth, so the prey is carried in by the barracuda's own forward motion.

Scientists from the Field Museum studied how a barracuda's jaws work. They examined barracuda from 20 g to 8.2 kg, dissected fresh specimens, and filmed biting at 1500 frames per second. In the barracuda's lower jaw, the muscles pull at the back of the jaw, a third class lever, which gives extra mechanical advantage there, according to the 2008 study of its bite. A computer model of the jaw predicted a bite force at the lower jaw of as high as 9 newtons in large barracuda. This is a prediction from jaw anatomy, not a force measured on a living fish.

To see how a barracuda's teeth bite, the scientists placed gelatin blocks in the mouths of barracuda specimens, closed the jaws by hand and then stained the blocks. At the back of the jaw, a strong palatine bone carries large triangular, blade-like teeth that face the lower jaw, so the two sets of teeth work together like scissors. Bite forces in great barracuda grow faster than body size, which suggests larger fish use the slicing bite more than small ones do.

In 2012, researchers captured 38 wild adult great barracuda in the Bahamas over six months. They tested muscle, liver and blood for ciguatoxins, using a laboratory cell test. Ciguatoxin is made by tiny reef algae-like organisms. Small fish eat them, and the toxin builds up in the bigger fish that eat those fish.

Blood and liver ciguatoxin levels in the barracuda rose and fell together (correlation 0.86), so a small blood sample can show whether a wild fish carries the toxin, without harming it. NOAA reports that about 60 percent of the 38 barracuda blood-sampled off Cape Eleuthera, Bahamas had ciguatoxin in them, a sign of recent exposure.

Scientists still do not agree on when and where great barracudas spawn. One source reports spring, another says it follows phases of the moon, and another says year-round except winter. The Florida Museum says the timing and place of great barracuda spawning have not been well documented. It is believed to take place in deeper, offshore waters.

Words to know

• lever: bar that pivots
• specimens: collected animals
• palatine: jaw bone
• ciguatoxin: natural toxin
• spawn: lay eggs