 Although referred to as “vocalization”, sounds are not actually made through laryngeal mechanics but are thought to be produced by contracting pairs of intrinsic sonic muscles in the swim bladder.The growling sound is a nocturnal vocalization emitted at night and singly, whereas the grunts is produced when the animals are grouped.Grunts sounds last 0.2 seconds and can be heard without any advice, their frequency range are from 250 to 300 Hz (Clara & Amorim, 2006).