Vocalisation has been recognised as one of the important modes of animal communication. In one anabantoid fish, the croaking gourami Trichopsis vittata, both sexes produce loud, croaking sounds during agonistic encounters and courtship. It is known that sound emission of this fish is mostly involved with the ritualised portion of the contest, which is likely to convey information between the opponents about their respective strength and status. The sound is produced by a complex mechanism that involves two modified tendons, located behind each pectoral fin. Due to the external position of these soft structures, parasites, sickness, or injury from fights can easily damage the tendons, leading to muteness. Reduction or even loss of the croaking ability may result in a substantial decreasing of the overall fitness. Experiments were designed to test whether or not croaking gouramis can repair damaged tendons and regain fully functional sound producing organs, as well as to evaluate the effect of muting and recovery on the outcomes of agonistic interactions. Fishes were muted by surgically cutting one or both the tendons that connect the "sonic'' muscle with the fin rays. The occurrence and timing of recovery was evaluated for 30 specimens of T. vittata after surgical muting. Croaking sounds produced by the fish were recorded during staged contests after recovery. Sound from each specimen was previously recorded before and after muting as well, for comparison. The elapsed time of reconnection of each tendon to the relative fin ray was also recorded. Some fishes were found to recover completely within less than 30 days, while others needed up to three months. However, evidence for the beginning of the recovery process was noticed as early as 4 days after operation. Behavioural performance after recovery was normal. Details of sounds produced and changes of behavioural repertoires are discussed (supported by National Organization for Hearing Research, NIMH-58198, Institute of Museum and Library Service-LL90187).
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