Cresci Alessandro
Department of Ocean Sciences, Rosenstiel School of Marine & Atmospheric Science, 4600 Rickenbacker Causeway, Miami, FL, 33149-1098, U.S.A.
Institute of Marine Research, Austevoll Research Station, Sauganeset 16, Storebø, N-5392, Norway.
Biol Rev Camb Philos Soc. 2020 Oct;95(5):1273-1286. doi: 10.1111/brv.12609. Epub 2020 May 13.
The European eel (Anguilla anguilla) is a catadromous fish that spawns in the Sargasso Sea. As larvae, eels cross the Atlantic Ocean and reach the continental slope of Europe, where they metamorphose into post-larval glass eels. These reach the continent, where some enter fresh water, some remain in marine waters, and others move between fresh and marine waters. After 5-25 years, as adult silver eels, they migrate back from fresh water to the Sargasso Sea to spawn and die. The glass eel stage is a critical step during which the eels cross the continental shelf and recruit to estuaries, where they facultatively transition to fresh water. Extensive research has been conducted to understand the behavioural mechanisms and environmental cues that aid and guide glass eels' migration. Glass eels follow odours and salinity gradients, they avoid light, and they change orientation and depth according to the tides. Recent work revealed that European glass eels also use Earth's magnetic field and lunar cues to orient. However, while we understand many aspects of their orientation behaviour, a unifying theory describing how glass eels migrate from the continental slope to fresh water is lacking. The goal of this review is to develop a comprehensive hypothesis on the migration of European glass eels, integrating previous knowledge on their orientation behaviour with recent findings on magnetic and celestial orientation. This review follows the journey of a hypothetical glass eel, describing the nature and the role of orientation cues involved at each step. I propose that, although glass eels have the sensory capacity to use multiple cues at any given time, their migration is based on a hierarchical succession of orientation mechanisms dictated by the physical properties of the environments that they occupy: (i) lunar and magnetic cues in pelagic water; (ii) chemical and magnetic cues in coastal areas; and (iii) odours, salinity, water current and magnetic cues in estuaries.
欧洲鳗鲡（Anguilla anguilla）是一种降河产卵洄游鱼类，在马尾藻海产卵。鳗鲡幼体穿越大西洋，抵达欧洲大陆架，在那里变态发育为幼鳗后期的玻璃鳗。这些玻璃鳗到达大陆后，一些进入淡水，一些留在海水中，还有一些在淡水和海水之间移动。5至25年后，成年银鳗从淡水洄游回马尾藻海产卵并死亡。玻璃鳗阶段是关键阶段，在此期间鳗鲡穿越大陆架并进入河口，在河口它们可以选择过渡到淡水环境。人们已经进行了广泛研究，以了解帮助和引导玻璃鳗洄游的行为机制和环境线索。玻璃鳗会追随气味和盐度梯度，它们避开光线，并根据潮汐改变方向和深度。最近的研究表明，欧洲玻璃鳗还利用地球磁场和月球线索来定向。然而，尽管我们了解它们定向行为的许多方面，但仍缺乏一个统一的理论来描述玻璃鳗如何从大陆架洄游到淡水环境。本综述的目的是基于欧洲玻璃鳗的洄游，提出一个综合假设，将先前关于其定向行为的知识与最近关于磁定向和天体定向的研究结果相结合。本综述追踪一条假设的玻璃鳗的洄游旅程，描述每个阶段所涉及的定向线索的性质和作用。我认为，尽管玻璃鳗在任何给定时间都具备利用多种线索的感官能力，但其洄游是基于由其所占据环境的物理特性所决定的定向机制的分层序列：（i）远洋水域中的月球和磁线索；（ii）沿海地区的化学和磁线索；以及（iii）河口的气味、盐度、水流和磁线索。
