The influence of aquatic surface respiration (ASR) on cardio-respiratory function of the serrasalmid fish Piaractus mesopotamicus |
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Authors: | Francisco Tadeu Rantin Cecilia Del Rosario Guerra Ana Lúcia Kalinin Mogens Lesner Glass |
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Institution: | aDepartamento de Ciências Fisiológicas, Universidade Federal de São Carlos, Via Washington Luiz, km 235, Caixa Postal 676, 13565-905 São Carlos SP, Brazil;bPrograma de Pós-Graduaçao em Ecologia e Recursos Naturais, Universidade Federal de São Carlos, Caixa Postal 676, 13565-905 São Carlos SP, Brazil;cDepartamento de Fisiologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, 14049-900 Ribeirão Preto SP, Brazil |
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Abstract: | When exposed to severely hypoxic water, many teleosts skim the better oxygenated surface layer (aquatic surface respiration, ASR). Information is scarce concerning the thresholds triggering ASR and its cardio-respiratory consequences. To assess the ambient conditions leading to ASR and to evaluate its effects on cardio-respiratory function, we exposed specimens of Piaractus mesopotamicus to gradual hypoxia (water oxygen tension ranging from 120 to 10 torr) with or, alternatively, without access to the surface. Concurrently, ASR, cardiac and respiratory frequencies, O2 uptake and gill ventilation were monitored. With surface access, ASR developed below the critical tension for O2 uptake (34 torr) by normal gill ventilation. Moreover, the time spent in ASR increased with prolonged hypoxic exposure to a maximum of 95% of total time. Without surface access, the species exhibited hypoxic bradycardia, that had not occurred in the group with fully developed ASR. Even without ASR, P. mesopotamicus recovered readily from hypoxic exposure, showing that this species possesses a number of mechanisms to cope with environmental hypoxia. |
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Keywords: | Aquatic surface respiration Critical O2 tension Heart frequency Hypoxia O2 uptake Piaractus mesopotamicus |
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