Physiology of sturgeon: effects of hypoxia and hypercapnia

Physiology is the study of key performance pathways between an organism's phenotypic design (structure) and its patterns of resource use and survival that determine its evolutionary fitness. Changes in environmental conditions (e.g. temperature, dissolved gases) may elicit physiological responses, with particular limits and potential costs (e.g. in redirecting energy from growth or reproduction) in fishes. The anadromous white sturgeon (WS) Acipenser transmontanus), is native to eastern North Pacific waters where some poorly-circulated inland systems may become hypoxic and some high-density culture systems hypercapnic. In this brief review of our research, we summarize the WS physiological responses to these variables. Juvenile WS (< 5 g wet weight) grew more slowly under moderate hypoxic stress ( dissolved oxygen ca. 58% of air-saturation), compared with normoxia, at all experimental temperatures ( 15, 20, and 25 C) apparently due to decreased food consumption rate. Hypoxia also decreased swimming activity and oxygen consumption rate in juvenile WS. Hypercapnic stress (45-75 mg CO2 L-1, pH = 7.0) also decreased juvenile WS growth, compared with normocapnic (0.52 mg CO2 L-1, pH = 8.0) and acidified wellwater (0.52 mg CO2 L-1, pH = 7.1) conditions, apparently due to decreased food consumption. Chronic hypercapnia also decreased blood O-2 affinity (Bohr effect), increased ventilation frequency as well as catecholamines and cortisol concentrations and caused a partially compensated respiratory acidosis. Finally, hypercapnia caused no significant change in gut blood flow, compared with normocapnia. However, hypercapnia increased stress-induced struggling, which significantly decreased gut blood flow. Further physiological studies are needed to better understand sturgeon environmental requirements in natural and culture-related settings ( including captive breeding programs to restore depleted populations), and their capabilities for dealing with increased negative anthropogenic pressures ( including habitat alterations) on their populations.