1. Introduction
Estuarine fish habitats are structured spatially by strong gradients in salinity, temperature and dissolved oxygen. While salinity and temperature variability are inherent features of most estuaries worldwide, hypoxia in shallow estuaries is a seasonal phenomenon, which has become more pervasive during the past century in populated areas, the likely consequence of anthropogenic organic enrichment (Officer et al., 1984 and Cooper and Brush, 1991a). Although high physiological plasticity is expected in estuarine species, strong effects of temperature, salinity and dissolved oxygen have been reported upon behavior, distribution, physiology, energetics, growth and surviva