Cardiorespiratory reflexes and aquatic surface respiration in the neotropical fish tambaqui (Colossoma macropomum): acute responses to hypercarbia

• Published in: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Vol. 174; no. 4; pp. 319 - 328
• Main Authors: Florindo, Luiz H, Reid, Stephen G, Kalinin, Ana L, Milsom, William K, Rantin, Francisco T
• Format: Journal Article
• Language: English
• Published: Germany Springer Nature B.V 01.05.2004
• Subjects: Analysis of Variance; Animals; Brazil; Carbon Dioxide - metabolism; Carbon Dioxide - pharmacology; Cardiovascular Physiological Phenomena; Colossoma macropomum; Dose-Response Relationship, Drug; Fish; Fishes - physiology; Gills - innervation; Heart rate; Heart Rate - drug effects; Hypoxia; Pulmonary Ventilation - drug effects; Pulmonary Ventilation - physiology; Reflex - drug effects; Reflex - physiology; Respiration; Brazil
• ISSN: 0174-1578; 1432-136X
• DOI: 10.1007/s00360-004-0417-5

We examined the cardiorespiratory responses to 6 h of acute hypercarbia (1, 2.5, and 5% CO(2)) in intact and gill-denervated (bilateral denervation of branchial branches of cranial nerves IX and X) tambaqui, Colossoma macropomum. Intact fish exposed to 1 and 2.5% CO(2) increased respiratory frequency ( f(R)) and ventilation amplitude ( V(AMP)) slowly over a 1- to 3-h period. Denervated fish did not show this response, suggesting that tambaqui possess receptors in the gills that will produce excitatory responses to low levels of hypercarbia (1 and 2.5% CO(2)) if the exposure is prolonged. The cardiac response to stimulation of these receptors with this level of CO(2) was a tachycardia and not a bradycardia. During exposure to 5% CO(2), intact fish increased f(R) and V(AMP), and showed a pronounced bradycardia after 1 h. After 2 h, the heart rate ( f(H)) started to increase, but returned to control values after 6 h. In denervated fish, the increase in f(R) was abolished. The slow increase in V(AMP) and the bradycardia were not abolished, suggesting that these changes arose from extra-branchial receptors. Neither intact nor denervated fish developed the swelling of the lower lip or performed aquatic surface respiration, even after 6 h, suggesting that these are unique responses to hypoxia and not hypercarbia.