Many cusk-eels and their relatives produce sound with their swim bladder, forward vertebrae (ver-teh-BREE), and the ligaments and muscles attached to those vertebrae. The swim bladder is an internal sac that fishes use to control their position in the water. Vertebrae are the bones that make up the spinal column. In some cusk-eels and their relatives, the swim bladder is hard and serves as an echo chamber. Some species make the sound just before mating.
Cusk-eels and their relatives usually hide in burrows or crevices or in or around invertebrate hosts during daylight hours and then exit at night to look for food. Some never leave the host and constantly feed on its internal organs.
Cusk-eels and their relatives either release eggs or bear live young. Eggs are released in open water and float individually or are deposited in a gummy raft. The egg rafts float at the ocean surface until they hatch, usually within several days. Larvae (LAR-vee) of some species float near the surface and sometimes travel great distances from their hatching place. Larvae are animals in an early stage and must change form before becoming adults.
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