Sound production is widespread among teleosts and is usually observed in social contexts. Many fish, such as triglids, produce sounds by contracting a pair of specialised striated muscles attached to both sides of the swimbladder wall, yielding low frequency sounds made up of repeated brief pulses. Temporal features of acoustic emissions can be controlled by the rate of muscle contraction, thus providing a rich means of conveying information. In this study the sound features of the grey (EutrigJa gurnardus), the streaked (Trigloporus lastoviza), the red (Aspitrigla cuculus) and the tub (Trigla Jucerna) gurnards were compared. The grey and the red gurnards emitted 3 different sound types, knocks, grunts and growls, whereas the streaked and the tub gurnards only emitted one sound type, growls and grunts respectively. Interspecific differences of calls were marked and based on the temporal patterning and on the grouping of the pulses. In the grey gurnard, ontogenetic changes in sound production were found. The sound production rate, the proportion of emitted sound type and the physical features of sounds varied with fish size. A study of diel and seasonal variations of sound production in the grey gurnard showed that more sounds were uttered during the day than at night and that grunts were more important and intense during the SpringSummer period. The sonic apparatus was examined in the species mentioned above and also in the large-scaled gurnard (Lepidotrigla cavillone) and the piper (Trigla lyra). The swimbladder and the sonic muscles grew throughout life in all species. Variations in the sonic apparatus with fish gender or time of the year were not detected. This suggests that the ability to vocalise is similar in both male and female gurnards, probably even during courtship. The shape of the swimbladder was species-specific. All species possessed a pair of intrinsic sonic muscles except for the piper whose sonic muscles were extrinsic. The pair of intrinsic sonic muscles of the grey gurnard contracted synchronously and each contraction generated a pulse of sound. The biological Significance of sound production was studied in the grey, the streaked and the tub gurnards. Few other studies have made a comparison of the behavioural context of sound production in different species of fish of the same family. Competitive feeding interactions were examined and compared between species. The different sound types emitted were also correlated with different behavioural categories. Typical sequences of behaviour were found in each species. Disputes over food items were settled by either reaching food first or by being aggressive, but never involved fighting escalation. The knocks of the grey gurnard and the growls of the streaked gurnard were associated with feeding and low levels of aggressive behaviour, and the grunts of grey and tub gurnards were associated with agonistic behaviour, such as approach, chase and frontal displays. The grey gurnard was the most vocal and aggressive species during competitive feeding. Smaller grey gurnards interacted more frequently than did larger fish, and a larger proportion of their interactions were accompanied by grunt calls. The metabolic costs of sound production in fish were calculated theoretically for different types of acoustic activity. If the assumptions made are valid then it seems that producing acoustic signals in fish is cheap. The biological implications of these low energetic costs were discussed. Finally, the acoustic repertoire of several non-triglid species of fish was examined. Sounds from 7 species were described for the first time. These species uttered sounds during territorial defence and courtship; contexts quite different from those studied for triglids.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:320240 |
| Date | January 1996 |
| Creators | Amorim, Maria Clara Correia de Freitas Pessoa de |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=232579 |
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