Lauren J. Chapman

Freshwater organisms face multiple threats to their ecosystems, including warming associated with climate change and low dissolved oxygen (environmental hypoxia), which are both increasing in frequency and extent in freshwater systems. Understanding tolerance thresholds for these environmental stressors as well as the plasticity of responses is the key for informing the conservation of imperilled species. Direct measurement of imperilled species can be difficult, and the use of surrogate (non-imperilled but closely related) species has been proposed as a remedy, but the degree to which surrogate data are representative of the imperilled species has not been widely validated. In this study, we measured physiological performance of two species: one federally listed as Threatened in Canada (Pugnose Shiner, Miniellus anogenus) and a non-imperilled congener (Blackchin Shiner, Miniellus heterodon). Hypoxia tolerance (critical oxygen tension and loss of equilibrium) and upper thermal tolerance (CT_max) were measured streamside over a period of 5 months. We found that the Threatened Pugnose Shiner had lower tolerance to both elevated temperature and hypoxia than the non-imperilled Blackchin Shiner. The species also differed in their responses to environmental dissolved oxygen (DO). CT_max of Pugnose Shiner had a positive relationship with DO such that CT_max was lowered when environmental DO was low, whereas there was no effect of DO on CT_max of Blackchin Shiner. Blackchin Shiner also showed plasticity of hypoxia tolerance in response to changes in environmental DO, while Pugnose Shiner showed little plasticity. We conclude that Pugnose Shiner may be more sensitive to heat waves and hypoxia associated with climate change. We also assert that researchers should be cautious when using surrogate species to inform tolerance limits of imperilled species and highlight the value of measuring imperilled species directly when possible. In this study, we investigated the use of Blackchin Shiner (Miniellus heterodon) as a surrogate species for the threatened Pugnose Shiner (Miniellus anogenus). We found Pugnose Shiner was less tolerant of high temperature and hypoxia, and we therefore caution the use of surrogate species to inform physiological tolerance thresholds.

Anthropogenic environmental degradation has led to an increase in the frequency and prevalence of aquatic hypoxia (low dissolved-oxygen concentration, DO), which may affect habitat quality for water-breathing fishes. The weakly electric black ghost knifefish, Apteronotus albifrons , is typically found in well-oxygenated freshwater habitats in South America. Using a shuttle-box design, we exposed juvenile A. albifrons to a stepwise decline in DO from normoxia (>95% air saturation) to extreme hypoxia (10% air saturation) in one compartment and chronic normoxia in the other. Below 22% air saturation, A. albifrons actively avoided the hypoxic compartment. Hypoxia avoidance was correlated with upregulated swimming activity. Following avoidance, fish regularly ventured back briefly into deep hypoxia. Hypoxia did not affect the frequency of their electric organ discharges. Our results show that A. albifrons is able to sense hypoxia at non-lethal levels and uses active avoidance to mitigate its adverse effects. Summary: The weakly electric knifefish, Apteronotus albifrons , avoids hypoxia below 22% air saturation. Avoidance correlates with increased swimming activity, but not with a change in electric organ discharge frequency.

Kininmonth, S., B. Crona, Ö. Bodin, I. Vaccaro, L. J. Chapman, and C. A. Chapman. 2016. Microeconomic relationships between and among fishers and traders influence the ability to respond to social-ecological changes in a small-scale fishery. Ecology and Society 22(2):26. https://doi.org/10.5751/ES-08833-220226

Downing, A. S., E. Van Nes, J. Balirwa, J. Beuving, P. Bwathondi, L. J. Chapman, I. J. M. Cornelissen, I. G. Cowx, K. Goudswaard, R. E. Hecky, J. H. Janse, A. Janssen, L. Kaufman, M. A. Kishe-Machumu, J. Kolding, W. Ligtvoet, D. Mbabazi, M. Medard, O. C. Mkumbo, E. Mlaponi, A. T. Munyaho, L. A. J. Nagelkerke, R. Ogutu-Ohwayo, W. O. Ojwang, H. K. Peter, D. Schindler, O. Seehausen, D. Sharpe, G. M. Silsbe, L. Sitoki, R. Tumwebaze, D. Tweddle, K. E. Van de Wolfshaar, H. Van Dijk, E. Van Donk, J. C. Van Rijssel, P. A. M. Van Zwieten, J. H. Wanink, F. Witte, and W. M. Mooij. 2014. Coupled human and natural system dynamics as key to the sustainability of Lake Victoria’s ecosystem services. Ecology and Society 19(4): 31.http://dx.doi.org/10.5751/ES-06965-190431

Oxygen availability in aquatic habitats is a major environmental factor influencing the ecology, behaviour, and physiology of fishes. This study evaluates the contribution of source population and hypoxic acclimatization of the African fish, Barbus neumayeri, in determining growth and tissue metabolic enzyme activities. Individuals were collected from two sites differing dramatically in concentration of dissolved oxygen (DO), Rwembaita Swamp (annual average DO 1.35 mgO2 L-1) and Inlet Stream West (annual average DO 5.58 mgO2 L-1) in Kibale National Park, Uganda, and reciprocally transplanted using a cage experiment in the field, allowing us to maintain individuals under natural conditions of oxygen, food availability, and flow. Fish were maintained under these conditions for four weeks and sampled for growth rate and the activities of phosphofructokinase (PFK), lactate dehydrogenase (LDH), citrate synthase (CS), and cytochrome c oxidase (CCO) in four tissues, liver, heart, brain, and skeletal muscle.

(2008). Biodiversity conservation in African inland waters: Lessons of the Lake Victoria region. SIL Proceedings, 1922-2010: Vol. 30, No. 1, pp. 16-34.