Sublethal effects of environmental change on tropical freshwater fish: responses of an electric fish to changes in dissolved oxygen and temperature

• Applicants: Professor Dr. Rüdiger Krahe; Dr. Stefan Mucha
• Subject Area: Sensory and Behavioural Biology ; Animal Physiology and Biochemistry ; Cognitive, Systems and Behavioural Neurobiology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539860011

As ectothermic animals, fish are directly affected by temperature fluctuations in their environment. In addition to natural temperature fluctuations, climate change and environmental pollution are causing increasingly warmer temperatures and lower oxygen concentrations in aquatic ecosystems. These two stressors - warm temperature and oxygen deficiency - reinforce each other, as the oxygen demand of ectothermic animals increases at warmer temperatures. Some species have evolutionarily adapted to a wider range of environmental conditions (e.g., species living in temperate regions subject to seasonal temperature fluctuations) and can better tolerate large changes in their environment than others (e.g., tropical species). For many species, we know little or nothing about how they cope with temperature fluctuations, where their tolerance limits lie, whether their cognitive abilities are affected, and how their metabolism - which relies mostly on oxygen as an energy source - is affected by temperature fluctuations. In this proposal, we aim to answer these questions that are both fundamental and of high current concern in the context of climate change using an African weakly electric fish. These animals generate electric fields in the surrounding water by discharging a special electric organ (EOD: electric organ discharge) and detect distortions in these fields caused by nearby objects or the EODs of conspecifics. By measuring the EODs of these fish, we can gain a quantitative insight into how much energy they invest in the electric sense (how many EODs does the fish produce?), how strong potential influences of environmental parameters are (what effect does temperature have on the EOD rate?), and how well they perceive their environment (do they react to changes in their electrosensory environment?). We will investigate in one species (Gnathonemus petersii) in four experiments (i) which temperatures they prefer and avoid, (ii) where their critical upper temperature limit lies, (iii) whether their ability to distinguish objects using their electric sense is impaired at warmer temperatures, and (iv) what influence temperature has on their oxygen consumption. Each experiment will be conducted twice: with fish acclimated to high oxygen concentrations and with the same fish after acclimating them to different oxygen concentrations for 8 weeks. After the second round of experiments, we will examine the morphology of the gills, enzyme activity, metabolite concentrations, and the expression of key genes in various tissues such as the brain, muscle, liver, heart, and electric organ. By doing so, we hope to find out what impact temperature and oxygen have on the entire animal - from behavior to gene expression, and how these two stressors interact.

• DFG Programme: Research Grants