Metabolic Energetics of Developing Fish from Different Thermal Habitats Exposed to Chronic and Acute Temperature...

Over 97% of ray-finned fish produce free-swimming larvae. With survival rates of less than 0.01% and radically different morphologies from adults, fish larvae play a crucial role in adapting to environmental changes and dispersing fish populations. Despite over a century of research, a critical gap remains in quantifying the energetic strategies of developing fish to determine how species from different thermal environments self-regulate in response to chronic and acute temperature changes and, the energetic costs associated with allostatic adjustments, referred to as allostatic load (RAL). This study examines the metabolic differences in yolk-sac larvae and their capacity to adjust to energetically adjust to chronic and acute temperature change. We studied the yolk-sac stages of two species: (1) zebrafish (Danio rerio, a tropical eurythermal freshwater fish) and (2) Atlantic cod (Gadus morhua, a cold-temperate stenothermal marine fish), under control (C) conditions (28°C for zebrafish and 5°C for Atlantic cod) and compared responses to larvae raised at chronic higher temperatures (31°C for zebrafish and 10°C for Atlantic cod) and exposed to acute temperature change for 1 h in a respirometer (3°C, zebrafish and 5°C, Atlantic cod) during the first week of larval life. Generally, both species exhibited higher metabolic rates and greater energetic-related changes in response to chronic stressors than to acute stressors compared to C conditions. While an acute increase in temperature resulted in some metabolic compensation, acute decrease in temperature led to what appeared to be metabolic dysregulation. Both species demonstrated higher variability in response to acute decreases in temperature compared to other treatments. Overall, the range of metabolic responsiveness was greater in Atlantic cod than in zebrafish, suggesting that stenothermal Atlantic cod have less resilience to changes in temperature than eurythermal zebrafish, at least at the yolk-sac stage and, during the first week of larval life when the yolk limits energy supply.