Lack of change in swimming capacity (Ucrit) following acute salinity exposure in juvenile shortnose sturgeon (Acipenser brevirostrum)

The role of salinity in recovery of white sturgeon (Acipenser transmontanus) from stimulated angling stress

White sturgeon (Acipenser transmontanus) in the Lower Fraser River are the focus of a catch-and-release angling fishery in British Columbia, Canada. However, the lower region of the catch area includes areas where tidal waters invade, and the consequence of salinity levels on recovery from an angling challenge are not characterized in sturgeon, despite theoretical implications of its import. We acclimated white sturgeon to various salinities (0, 10 and 20‰ (parts per thousand)) to investigate the effects of acclimation on recovery from stimulated angling stress that was induced through manual chasing. This challenge elicited the traditional physiological responses such as ion homeostasis disturbance, increases in secondary stress indicators and metabolic acidosis; however, environmental salinity altered the timing of recovery in some of the parameters measured. In addition, the severity of the intracellular pH disturbance in both heart and red blood cell seemed to be mediated in fresh water, yet the recovery pattern of plasma chloride and bicarbonate ions seemed to be facilitated by higher salinity. In general, responses were similar but not identical, leading us to conclude that the role of salinity on recovery from exercise is complex but not insignificant. Salinity may be important to behaviours exhibited by white sturgeon (such as migrations) in their respective saline environments, but less so around the impact of an angling stressor. Further exploration of this response may provide insight on whether the current tidal boundaries for angling white sturgeon are appropriate.

Atlantic sturgeon and shortnose sturgeon exhibit highly divergent transcriptomic responses to acute heat stress

In comparison to most modern teleost fishes, sturgeons generally display muted stress responses. While a muted stress response appears to be ubiquitous across sturgeon species, the mechanisms unpinning this muted response have not been fully described. The objective of this study was to determine the patterns of hematological and transcriptomic change in muscle tissue following an acute high temperature stress (critical thermal maxima; CT_max) in two locally co-occurring but evolutionarily distant sturgeon species (Atlantic and shortnose sturgeon). The most striking pattern found was that Atlantic sturgeon launched a vigorous transcriptomic response at CT_max, whereas shortnose sturgeon did not. In contrast, shortnose sturgeon have significantly higher cortisol than Atlantics at CT_max, reconfirming that shortnose have a less muted cortisol stress response. Atlantic sturgeon downregulated a number of processes, included RNA creation/processing, methylation and immune processes. Furthermore, a number of genes related to heat shock proteins were differentially expressed at CT_max in Atlantic sturgeon but none of these genes were significantly changed in shortnose sturgeon. We also note that the majority of differentially expressed genes of both species are undescribed and have no known orthologues. These results suggest that, while sturgeons as a whole may show muted stress responses, individual sturgeon species likely use different inducible strategies to cope with acute high temperature stress.

Repeat UCrit and endurance swimming in juvenile shortnose sturgeon (Acipenser brevirostrum)

Previous results show that juvenile shortnose sturgeon are steady swimmers and, compared with salmonids, generally have low critical swimming (UCrit) and endurance swimming capacities. Most studies on swimming capacities of sturgeon, and other fishes, include those where fish have only been swum once and the metrics of swimming performance are assessed (e.g., time swum, speed achieved). Under natural conditions, there are ample instances where fish undergo multiple swimming cycles when traversing fish ways, culverts and other sources of fast water flow. While some evidence exists for salmonids, the effects of repeat swimming are not well known for sturgeon. The current study consisted of two experiments. The first examined the UCrit of juvenile shortnose sturgeon following three consecutive swimming trials with a 30 min recovery period between subsequent tests. The second examined the endurance swimming capacities of juvenile shortnose sturgeon following three consecutive swimming trials with a 60 min recovery period between subsequent tests. Our findings indicate that (i) UCrit was consistent (~2 body lengths/s) among swimming trials; (ii) significant individual variation exists between individuals in the endurance swimming trials; and (iii) consistent results exist for individuals across swimming trials in both the UCrit and the endurance swimming tests. These results suggest that juvenile shortnose sturgeon have a high recovery capacity, and their behaviour and morphology likely reflect aspects of their swimming capacities.