Coping with climate change: Phenotypic plasticity in an imperilled freshwater fish in response to elevated water temperature

• Published in: Aquatic conservation 2021-10, Vol.31 (10), p.2726-2736
• Main Authors: Potts, Lindsay B., Mandrak, Nicholas E., Chapman, Lauren J.
• Format: Article
• Language: English
• Subjects: Acclimation; Acclimatization; Breeding; Captive breeding; Climate change; Endangered & extinct species; endangered species; Environmental changes; Exposure; Fish; Fresh water; Freshwater; Freshwater fish; Freshwater fishes; gill morphology; Gills; High temperature; Hypoxia; Individual rearing; Inland water environment; Juveniles; lake; Notropis anogenus; Oxygen; Oxygen consumption; Oxygen uptake; Phenotypic plasticity; physiology; Plastic properties; Plasticity; pugnose shiner; river; Sensitivity analysis; Temperature effects; Temperature tolerance; Thermal stress; thermal tolerance; Threatened species; Uptake; Water temperature
• ISSN: 1052-7613; 1099-0755
• DOI: 10.1002/aqc.3620

Climate change has emerged as an increasingly important threat to freshwater systems. To cope with rapidly changing thermal regimes, freshwater fishes must either relocate or adjust through genetic adaptation and/or phenotypic plasticity. Short‐term responses to elevated water temperature have been well studied in freshwater fishes; however, far less is understood about change induced by long‐term exposure. Furthermore, few studies have investigated the effects of temperature on already imperilled species, which may be more sensitive to environmental change. This study investigated the effects of rearing temperature on critical thermal maximum (CTmax), agitation temperature (Tag, temperature at which fish show behavioural signs of thermal stress) and gill size in pugnose shiner, Notropis anogenus, a threatened species in Canada. Juvenile pugnose shiner were reared for 4 months across five different ecologically relevant temperatures. CTmax and Tag were measured under normoxia and acute exposure to hypoxia to test for oxygen sensitivity of the upper thermal limits in this species. CTmax increased with elevated water temperature. Tag also increased with rearing temperature and occurred, on average, 4.3°C above acclimation temperatures. The CTmax and Tag were lower when fish were exposed acutely to hypoxia. Interestingly, gill size (e.g. total gill filament length) increased with rearing temperature, which may increase oxygen uptake capacity and support increased metabolic demands of warmer waters. Overall, pugnose shiner show plasticity in several traits in response to long‐term exposure to elevated water temperature that may facilitate persistence in warmer waters. However, acute hypoxia exposure reduced thermal tolerance, stressing the importance of evaluating interactive effects of multiple stressors. Identifying source populations of pugnose shiner with greater thermal tolerance or implementing captive breeding under higher temperature regimes may improve the success of re‐introduction efforts in the face of climate change, but the consequences to fitness of increased thermal tolerance should be examined.