Body mass, length, oxygen consumption (O₂) and heart rate (f_H) were measured in "embryos" (prior to hatching), "larvae" (days 10-20), "juveniles" (days 30-70 in 10-day intervals), and "adults" (day 100) of the zebrafish Danio rerio. Fish were chronically reared at either 25, 28, or 31°C and then acutely exposed to hypoxia at different developmental stages. We hypothesized that at any given rearing and measurement temperature, D. rerio would maintain O₂ at lower ambient PO₂ [i.e., have a lower critical partial pressure (P_crit)] as development progressed and that at any given developmental stage individuals reared and measured at higher temperatures would show a more pronounced hypoxic bradycardia. O₂ in normoxic fish at 28°C peaked at ~40 µmol · g¹ · h¹ at day 10, thereafter falling to 4-5 µmol · g¹ · h¹ at day 100. The Q₁₀ for O₂ was 4-5 in embryos, falling to 2-3 from day 10 to day 60 and rising again to 4-5 at day 100. P_crit at 28°C was ~80 mmHg in embryos but decreased sharply to 20 mmHg at 100 days, supporting the hypothesis that more mature fish would be better able to oxygen regulate to lower ambient PO₂ levels. P_crit increased sharply with measurement temperature. Heart rate (f_H) at 28°C increased from about 125 beats/min in embryos to a peak of ~175 beats/min at days 10-30 and then fell to ~130 beats/min by day 100. Unlike for O₂, the Q₁₀ for f_H was more constant at 1.2-2.5 throughout development. Hypoxic exposure at any temperature had no effect on f_H until ~day 30, after which time a hypoxic bradycardia was evident. As evident for O₂, the bradycardia in older larvae was more profound at higher temperatures. On the assumption that bradycardia is indicative of hypoxic stress, the increasing prevalence of a hypoxic bradycardia in older, warmer individuals supports the hypothesis that increasing hypoxic susceptibility with development would be exacerbated by increasing temperature. Collectively, these data indicate that the ability to regulate O₂ and f_H in response to the compounding demands of increased temperature and/or decreased oxygen availability first develops after ~20 days in D. rerio and, thereafter, the ability to maintain O₂ in the face of ambient hypoxia progressively builds through to adulthood. Additionally, the temperature responses of metabolism and heart rate differ substantially at different phases of development, suggesting a loose coupling between the respiratory and cardiovascular systems, at least early in development.

development; hypoxia; embryos

This article has been cited by other articles:

				P. M. Craig, C. M. Wood, and G. B. McClelland Gill membrane remodeling with soft-water acclimation in zebrafish (Danio rerio) Physiol Genomics, June 19, 2007; 30(1): 53 - 60. [Abstract] [Full Text] [PDF]

				P. R. Biga and F. W. Goetz Zebrafish and giant danio as models for muscle growth: determinate vs. indeterminate growth as determined by morphometric analysis Am J Physiol Regulatory Integrative Comp Physiol, November 1, 2006; 291(5): R1327 - R1337. [Abstract] [Full Text] [PDF]

				D. H. Evans, P. M. Piermarini, and K. P. Choe The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste Physiol Rev, January 1, 2005; 85(1): 97 - 177. [Abstract] [Full Text] [PDF]

				M. G Jonz, I. M Fearon, and C. A Nurse Neuroepithelial oxygen chemoreceptors of the zebrafish gill J. Physiol., November 1, 2004; 560(3): 737 - 752. [Abstract] [Full Text] [PDF]

				B. Bagatto, B. Pelster, and W. W. Burggren Growth and metabolism of larval zebrafish: effects of swim training J. Exp. Biol., March 14, 2002; 204(24): 4335 - 4343. [Abstract] [Full Text] [PDF]