Abstract

Hypoxia-temperature interactions can have major effects upon fish physiology and energetics. In estuarine species, such effects can be also modified by natural salinity gradients leading to a three-way habitat contraction under extreme conditions. In this paper we use Fry's paradigm to propose an explanatory framework and to expand traditional mass balance bioenergetic models, incorporating dissolved oxygen and salinity effects. Water temperature was modeled as the controlling factor that establishes maximum potential rates and minimum oxygen demand; dissolved oxygen was considered to constrain physiological responses whenever oxygen demands exceed oxygen delivery rates; salinity was incorporated as a masking (loading) factor, demanding both energy and oxygen for osmoregulation processes. This general framework was expressed as a set of algorithms, with a total of 30 parameters, which were estimated using results from a large set of laboratory experiments conducted on young-of-the-year and yearling Atlantic sturgeons, as well as from other published studies. Compared to an empirical quadratic fit of these laboratory data, the model was more informative (lower AIC), suggesting that measured responses followed theoretical expectations. The model was tested in mesocosm trials, where strong correlations were observed between predicted and observed monthly and seasonal growth rates but modest to poor correlations were observed for predicted daily instantaneous growth rate. Sensitivity tests showed that uncertainty in activity cost and food consumption ratio parameters contributed most to model error. © 2009 Elsevier B.V. All rights reserved.