Lurking in the crevices of their coral reef home, moray eels take a different approach when it comes to dining. Most fish are suction feeders,however morays prefer to pounce on and bite their victims with a fearsome set of razor sharp teeth. Wanting to know more about morays' eating habits, Rita Mehta and Peter Wainwright from the University of California, Davis, measured morays' skull and jaw movements as they fed, and tested their idea that biting allows morays greater flexibility in the timing and movements of their jaws when they're capturing their prey().
To suction feed, `fish have to generate a negative pressure, by rapidly expanding the mouth cavity; one way to do this is to depress the floor of the mouth' says Mehta. An important head muscle, which helps lower the floor of the mouth, is the sternohyoideus muscle, which is found between the bony pectoral girdle and the skull and moves a bone called the hyoid. The sternohyoideus muscle and the hyoid bone are large and robust in suction feeders, but morays have a very reduced and thin hyoid bone, and small sternohyoideus muscle. This means that `eels aren't able to lower the floor of the mouth', Mehta explains; they can't generate suction strong enough to feed.
Having shown that the sternohyoideus and hyoid of morays weren't up to the challenge of generating pressures strong enough to suck in prey, the team wanted to confirm that morays rely on biting rather than suction to feed. They filmed the morays feeding on juicy squid pieces, tracking the movements of six points on the skull and jaw. They compared the morays' feeding movements to those in a closely related suction feeding eel, distantly related suction feeding freshwater sunfish, and a cichlid.
Comparing the moray's skull movements with the suction feeders, they found that jaw and skull movements were different in morays to the other fish species. While the suction feeders all fed in a very similar way, morays had a wide repertoire of skull movements to capture prey. They would sometimes overshoot the target, correcting their meal-grabbing movements by reversing their direction, and then coming at their prey from a variety of directions and angles.
On the other hand, the suction feeders lined themselves up directly in front of their targets. The team saw the mouth floor lowering in suction feeders, and the squid morsels moved towards their mouths just before they grabbed them, both indicating that they were expanding their mouths and generating suction.
However, it took morays up to 10 times longer – 500 ms – to bite their prey than the suction feeders took to hoover up the squid pieces. While biting is slower than sucking, `you don't necessarily have to be so precise, and you can go for bigger things' says Mehta. The team suspect that biting allows morays to be successful predators in the confined spaces in reef crevices; they can munch on larger prey to fuel their bodies, and attack their victims from many different angles.
