Developmental cardiorespiratory physiology of the air-breathing tropical gar, Atractosteus tropicus

• Published in: American journal of physiology. Regulatory, integrative and comparative physiology Vol. 311; no. 4; pp. R689 - R701
• Main Authors: Burggren, Warren W, Bautista, Gil Martinez, Coop, Susana Camarillo, Couturier, Gabriel Márquez, Delgadillo, Salomón Páramo, García, Rafael Martínez, González, Carlos Alfonso Alvarez
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.10.2016
• Subjects: Animals; Atractosteus tropicus; Developmental biology; Fish; Fishes - embryology; Fishes - physiology; Gills - embryology; Gills - physiology; Heart - embryology; Heart - physiology; Heart rate; Heart Rate - physiology; Hypoxia; Larva - physiology; Lung - embryology; Lung - physiology; Physiology; Respiration; Respiratory Mechanics - physiology; Temperature effects; development; heart rate; larval fish; respiration; tropical gar
• ISSN: 0363-6119; 1522-1490
• DOI: 10.1152/ajpregu.00022.2016

The physiological transition to aerial breathing in larval air-breathing fishes is poorly understood. We investigated gill ventilation frequency (f ), heart rate (f ), and air breathing frequency (f ) as a function of development, activity, hypoxia, and temperature in embryos/larvae from day (D) 2.5 to D30 posthatch of the tropical gar, Atractosteus tropicus, an obligate air breather. Gill ventilation at 28°C began at approximately D2, peaking at ∼75 beats/min on D5, before declining to ∼55 beats/min at D30. Heart beat began ∼36-48 h postfertilization and ∼1 day before hatching. f peaked between D3 and D10 at ∼140 beats/min, remaining at this level through D30. Air breathing started very early at D2.5 to D3.5 at 1-2 breaths/h, increasing to ∼30 breaths/h at D15 and D30. Forced activity at all stages resulted in a rapid but brief increase in both f and f , (but not f ), indicating that even in these early larval stages, reflex control existed over both ventilation and circulation prior to its increasing importance in older fishes. Acute progressive hypoxia increased f in D2.5-D10 larvae, but decreased f in older larvae (≥D15), possibly to prevent branchial O loss into surrounding water. Temperature sensitivity of f and f measured at 20°C, 25°C, 28°C and 38°C was largely independent of development, with a Q between 20°C and 38°C of ∼2.4 and ∼1.5 for f and f , respectively. The rapid onset of air breathing, coupled with both respiratory and cardiovascular reflexes as early as D2.5, indicates that larval A. tropicus develops "in the fast lane."