Temperature, hypoxia, and mycobacteriosis: effects on adult striped bass Morone saxatilis metabolic performance

Abstract

Mycobacteriosis, a chronic bacterial disease of fishes, is prevalent in adult striped bass from Chesapeake Bay (USA). Although environmental factors may play a role in disease expression, the interaction between the disease and environmental stress remains unexplored. We therefore examined the individual and interactive effects of elevated temperature, hypoxia, and mycobacteriosis on the metabolism of wild-caught adult striped bass from Chesapeake Bay using respirometry. Because the spleen is the primary target organ of mycobacteriosis in striped bass, we hypothesized that the disease interferes with the ability of fish to increase their hematocrit in the face of increasing oxygen demands. We determined standard metabolic rate (SMR), maximum metabolic rate under normoxia (MMRN), critical oxygen saturation (S(crit)), and MMR under hypoxia (3 mg O(2) l-1: MMR(H)) for healthy and visibly diseased fish (i.e. exhibiting skin lesions indicative of mycobacteriosis). Measurements were taken at a temperature within the preferred thermal range (20°C) and at an elevated temperature (28°C) considered stressful to striped bass. In addition, we calculated aerobic scope (AS(N) = MMR(N) - SMR, AS(H) = MMR(H) - SMR) and factorial scope (FS(N) = MMR(N) SMR-1, FS(H) = MMR(H) SMR-1). SMR increased with increasing temperature, and hypoxia reduced MMR, AS, and FS. Mycobacteriosis alone did not affect either MMR(N) or MMR(H). However, elevated temperature affected the ability of diseased striped bass to tolerate hypoxia (S(crit)). Overall, our data indicate that striped bass performance under hypoxia is impaired, and that elevated water temperatures, hypoxia, and severe mycobacteriosis together reduce aerobic scope more than any of these stressors acting alone. We conclude that the scope for activity of diseased striped bass in warm hypoxic waters is significantly compromised.

Warm acclimation and oxygen depletion induce species-specific responses in salmonids

“…This reduction is more severe than expected based on the OCLTT model (McBryan et al, 2013). Acute thermal stress also increased the oxygen tension, in that a significant reduction in metabolic rate was observed (critical oxygen tension) in summer flounder (Paralichthys dentatus) and striped bass (Morone saxatilis) (Capossela et al, 2012;Lapointe et al, 2014). In contrast, moderate, acute heat shock increased hypoxia tolerance in tidepool sculpins (Oligocottus maculosus), but hypoxia tolerance was reduced with a more severe thermal shock (Todgham et al, 2005).…”

“…In agreement with the model, there are findings that temperature tolerance decreases in hypoxic conditions (Verberk et al, 2013) and that high temperatures reduce hypoxia tolerance (e.g. Capossela et al, 2012;McBryan et al, 2013;Lapointe et al, 2014). However, there is ongoing debate about the suitability of the OCLTT model for all ectothermic animals (see Clark et al, 2013 and correspondence on that article).…”

The competing impacts of climate change and nutrient reductions on dissolved oxygen in Chesapeake Bay

“…In light of this, the impact on the TMDL of a decrease in oxygen concentrations due to climate change should be viewed in conjunction with the impact increased temperature is likely to have on the species upon which the DO levels in the TMDL nutrient reductions were predicated. Multiple studies have established that increasing water temperature increases metabolic rates in fish that cause them to experience negative health impacts at higher DO concentrations than they do at lower temperatures (Breitburg, 2002;Portner and Lanning, 2009;Lapointe et al, 2014). Due to those compounding impacts and the large role temperature is expected to play in regulating future DO, it may be prudent for the TMDL to elevate the mandated minimum DO levels in an effort to protect target species.…”

The competing impacts of climate change and nutrient reductions on dissolved oxygen in Chesapeake Bay

“…In light of this, the impact on the TMDL of a decrease in oxygen concentrations due to climate change should be viewed in conjunction with the impact increased temperature is likely to have on the species upon which the DO levels in the TMDL nutrient reductions were predicated. Multiple studies 450 have established that increasing water temperature increases metabolic rates in fish that cause them to experience negative health impacts at higher DO concentrations than they do at lower temperatures (Breitburg, 2002;Portner and Lanning, 2009;Lapointe et al, 2014). Due to those compounding impacts and the large role temperature is expected to play in regulating future DO, it may be prudent for the TMDL to elevate the mandated minimum DO levels in an effort to protect target species.…”