Freshwater eels are of tropical marine origin and have spread worldwide. Of the 19 recognised species or subspecies, all 6 temperate species are listed within IUCN Threatened Species categories, together with 7 tropical species. Many reasons have been advanced to explain the significant declines of eels including habitat fragmentation and loss, spread of parasites and diseases, pollution, impacts of hydro dams, overfishing and oceanic changes. The present paper reviews some of the unique life history characteristics of Anguillids—fecundity and semelparous spawning, adaptability, resilience, and being energetically conservative—but despite such remarkable adaptations, according to the IUCN the genus is facing possible extinction. It is suggested that Anguillid life history strategies rely on two additional components—environmental determination of sex, and the need for surplus production (the Surplus Production Hypothesis, SPH). Surplus production is required to counteract the many hazards that eels face throughout an often long and complex life history. Recruitment of temperate species has fallen by over 90%, and resulting lower densities of juvenile eels in tidal and lower river reaches provides less incentive for upstream migration and dispersal. Female eels are generally found further inland than males, with development of sex associated with lower densities. With fewer juveniles migrating to inland areas, the numbers of females will become reduced, and further compound the reduced spawner biomass and consequent reduced recruitment of glass eels. The SPH hypothesis emphasises the importance of conservative harvest of glass eels, habitat connectivity, the need to ensure maximum female escapement, and the importance of stocking inland waterways with juvenile eels.

淡水鳗鱼起源于热带海洋，并已在世界范围内传播。在19个公认的物种或亚种中，所有6个温带物种都被列为IUCN濒危物种类别，另外还有7种热带物种。已经提出了许多原因来解释鳗鱼的大量减少，包括栖息地的破碎和丧失，寄生虫和疾病的传播，污染，水坝的影响，过度捕捞和海洋变化。本文回顾了美洲虎的一些独特的生活史特征-繁殖力和分生卵，适应性，适应力和精力充沛的保守性-但尽管这种适应性很强，但根据自然保护联盟的说法，该属正面临灭绝的可能。有人认为，安圭利人的生活史策略还依赖于两个额外的组成部分：环境决定性别，以及对剩余生产的需求（剩余生产假说，SPH）。为了应对鳗鱼在漫长而复杂的生命历程中面临的许多危害，需要增加产量。温带物种的招募量下降了90％以上，因此潮汐和下游河道中的幼鳗密度降低，对上游迁移和扩散的刺激作用减弱。通常发现雌性鳗鱼比雄性更靠近内陆，性别发展与密度降低有关。随着更少的幼鱼迁移到内陆地区，雌性的数量将减少，并且使产卵生物量减少以及玻璃鳗的补充减少进一步加剧。