Comparative analyses of metabolic responses to temperature and starvation in the freshwater species, roach, Rutilus rutilus (L.), and burbot, Lota lota (L.)

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In temperate habitats, seasonal temperature cycles influence fish feeding and fasting behaviors, necessitating various behavioral and metabolic adaptations. This study investigates starvation strategies in freshwater fish, specifically roach (Rutilus rutilus) and burbot (Lota lota), under seasonal temperature fluctuations. Roach, a typical winter-fasting species, contrasts with burbot, which exhibits unusual thermal tolerance and restricted foraging behavior in summer. Both species showed negative growth rates during starvation, with responses varying by temperature and species. Oxygen consumption measurements revealed that roach had a higher thermal sensitivity (Q10 = 2.7) than burbot (Q10 = 1.9). Warm-acclimated roach exhibited a delayed response to starvation, while burbot experienced immediate metabolic depression. Energy reserves were analyzed in liver and muscle tissues, showing that energy consumption correlated with natural fasting periods. Roach utilized hepatic fuels before muscle lipids, while burbot relied heavily on hepatic lipid reserves to sustain fasting. Cellular analyses indicated that roach did not adjust aerobic and biosynthetic capacities in response to temperature changes, whereas burbot demonstrated thermal compensation at low temperatures. Overall, the study highlights differential thermal tolerances and metabolic adaptations in roach and burbot, emphasizing the importance of comparative approaches in u