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Abstract
The alarm response to skin extract has been well documented in fish. In response to skin extract, there is a decline in both locomotion activity and aggressive interactions. Our observation herein of these responses in the cichlid Nile tilapia, Oreochromis niloticus, confirmed the existence of the alarm response in this species. However, so far there has been a paucity of information on the autonomic correlates of this response. In this study, the ventilatory change in response to the chemical alarm cue was evaluated. This parameter was measured 4 min before and 4 min after exposure to 1 mL of either conspecific skin extract or distilled water (extract vehicle). Skin extract induced an increase in the ventilation rate, which suggested an anticipatory adjustment to potentially harmful stimuli. The chemical cue (alarm substance) also interfered with the prioritisation of responses to different environmental stimuli (stimuli filtering); this was suggested by the observation that the Nile tilapia declined to fight after exposure to a cue that indicates a risk of predation. Furthermore, histological analysis of the Nile tilapia skin revealed the presence of putative alarm substance-producing (club) cells.
Acknowledgements
The authors are grateful for the indispensable technical assistance of Aparecida de Souza Fim Pereira. This study, which was part of Rodrigo E. Barreto's post-doctoral research, was carried out at FMRP–USP post-doctoral programme under the supervision of Anette Hoffmann. It was financially supported by Fundação de Amparo à Pesquisa do Estado de São Paulo–FAPESP (Process: 2005/04771-5).