Effect of Nutritional Status on the Osmoregulation of Green Sturgeon (Acipenser medirostris)

Abstract

Anthropogenic climate change is linked to food web and salinity fluctuations in estuarine environments. Both decreased nutritional status and environmental salinity influence the physiological tolerance and health of fish populations; however, limited information on the interaction of these two factors and their physiological consequences is available. The green sturgeon (Acipenser medirostris) is a species of special concern in California, and the southern distinct population segment is listed as threatened. To test the hypothesis that poor nutrition negatively affects osmoregulation, juvenile green sturgeon (222 d posthatch) were randomly assigned to four feed restriction groups (12.5%, 25%, 50%, and 100% of the optimal feeding rate for 4 wk). Fish were then acutely exposed to 0-, 8-, 16-, or 32-ppt salinities and sampled at three time points (12, 72, or 120 h). Feed restriction significantly (P < 0.05) decreased specific growth rate, feed efficiency, condition factor, whole-body lipids, and protein content as well as plasma glucose, triglycerides, and proteins. Furthermore, feed restriction, salinity concentration, and salinity exposure time had significant effects on hematological indexes (hematocrit, hemoglobin), plasma values (osmolality, Na(+), K(+), Cl(-), glucose, lactate, cortisol), enzymatic activity (gill and pyloric ceca Na(+)/K(+) ATPase), and morphology of gill mitochondria-rich cells. The largest disturbances were observed at the highest salinity treatments across all feeding regimes. In addition, the interaction between feed restriction and acute salinity exposure at the highest salinity treatment resulted in high mortality rates during the first 72 h of salinity exposure. Evaluating the interactions of these environmental stressors and their implications on green sturgeon physiological tolerance will inform restoration and management efforts in rapidly changing estuarine environments.

A feeding experiment using captive green sturgeon (Acipenser medirostris Ayres, 1854): Testing non-invasive methods to assess condition and growth

“…Additionally, our results are consistent with previous results in juvenile green sturgeon from Haller et al. (), who also found that whole body fat gradually decreased when ration was restricted from 100% optimal feeding rate (OFR) to 25% OFR, but that whole body protein decreased when ration was further restricted to 12.5% OFR. These results, combined with the decline in body weight and condition factor observed in the 0.1% body weight/day treatment, suggest that the low ration had profound effects on the condition of the experimental sturgeon.…”

Effects of feed restriction on the upper temperature tolerance and heat shock response in juvenile green and white sturgeon

“…Details of rearing practices for green and white sturgeon can be found in Haller et al (2015) and Lee et al (2015), respectively. All handling, care, and experimental procedures were approved by the UC Davis Institutional Animal Care and Use Committee (Protocol #16541).…”

“…Maintenance of good nutritional status is critical because foodlimited fish are more susceptible to predation (Metcalfe et al, 1998;Steele, 2001), disease (Oliva-Teles, 2012), and other environmental factors (e.g., salinity; Haller et al, 2015;Lee et al, 2015). Energy allocation to different molecular and cellular pathways essential to the stress response can be limited in fish with reduced nutritional status (i.e., physiological trade-offs), resulting in decreased stress tolerance (Sokolova, 2013).…”

Sublethal salinity stress contributes to habitat limitation in an endangered estuarine fish

“…Shifts in phytoplankton and zooplankton communities in conjunction with increasing invasive species richness and abundance has greatly altered food web dynamics in the SFE (Cloern and Jassby ), emphasizing the importance of ecological interactions in understanding global change impacts on SFE native species (Haller et al. ; Lee et al. ).…”

“…However, given that delta smelt actually possess the physiological 'machinery' to cope with conditions outside this range, but cofactors such as energetic costs may play critical roles limiting their performance, it may be beneficial to also focus efforts on other ecological factors (e.g., food resource supply and community structure). Shifts in phytoplankton and zooplankton communities in conjunction with increasing invasive species richness and abundance has greatly altered food web dynamics in the SFE (Cloern and Jassby 2012), emphasizing the importance of ecological interactions in understanding global change impacts on SFE native species (Haller et al 2014;Lee et al 2015). While inclusion of multiple stressors and ecological complexities is challenging, the absence of considering them may lead to ineffective management actions (e.g., population decline despite maintenance of the LSZ zone, due to inadequate food supply or adaptation of marine predators allowing them to expand into LSZ waters).…”