Energetic condition is one of the most important factors that influence fitness and reproductive performance in vertebrates. Yet, we lack evidence on how energetic states change in response to reproduction in large marine vertebrates. In the present study, we used a non-lethal approach to assess relationships among reproductive stage, circulating steroid hormones (testosterone and relative corticosteroid levels), plasma fatty acids, and the ketone body β-hydroxybutyrate in male sharks of two species with divergent ecologies, the benthic nurse shark (Ginglymostoma cirratum) and the epipelagic blacktip shark (Carcharhinus limbatus). We found higher relative corticosteroid levels in adult nurse sharks during the pre-mating period and in blacktip sharks during the mating period. Higher levels of β-hydroxybutyrate were found in adult nurse sharks during the mating period, but concentrations of this ketone body did not significantly vary across reproductive stages in blacktip sharks. We also detected reduced percentages of essential fatty acids during the mating period of both nurse and blacktip sharks. Taken together, our findings suggest that nurse and blacktip sharks differ in their energetic strategy to support reproduction, however, they likely rely on physiologically important fatty acids during mating, to support spermatogenesis.

精力充沛是影响脊椎动物健康和繁殖性能的最重要因素之一。然而，我们缺乏关于能量状态如何响应大型海洋脊椎动物繁殖而变化的证据。在本研究中，我们使用非致死性方法来评估两种生态环境不同的雄性鲨鱼的生殖阶段、循环类固醇激素（睾酮和相对皮质类固醇水平）、血浆脂肪酸和酮体 β-羟基丁酸之间的关系, 底栖护士鲨 ( Ginglymostoma cirratum ) 和上层黑鳍鲨 ( Carcharhinuslimbatus )）。我们在交配前的成年护士鲨和交配期间的黑鳍鲨中发现了较高的相对皮质类固醇水平。在交配期间在成年护士鲨中发现了更高水平的 β-羟基丁酸，但这种酮体的浓度在黑鳍鲨的繁殖阶段没有显着变化。我们还检测到护士鲨和黑鳍鲨在交配期间必需脂肪酸的百分比降低。综上所述，我们的研究结果表明，护士鲨和黑鳍鲨在支持繁殖的能量策略上有所不同，但是，它们可能在交配过程中依赖生理上重要的脂肪酸来支持精子发生。