Sex differentiation and sex determination in eels: consequences for management
Authors: GeffroyB, Bardonnet A (2016), Sex differentiation and sex determination in eels: consequences for management.
Publication: Fish and Fisheries, 17: 375–398. doi: 10.1111/faf.12113
The aim of this review is to present an overview of the sex differentiation and sex determination processes in eels in relation to the urgent need to provide scientific knowledge to better protect and manage the Anguilla genus. Indeed, the global decline of the three main temperate eel stocks, Anguilla anguilla, Anguillidae (Fisheries Management and Ecology, 2003, 10, 365); Anguilla japonica, Anguillidae (Casselman, Eel Biology, Springer Japan, 2003, 293) and Anguilla rostrata, Anguillidae (Tatsukawa, Eel Biology, Springer, Japan, 2003, 255), raises concerns about the necessity to better understand all stages of the life cycle of eels (Righton and Walker, Journal of Fish Biology, 2013, 83, 754).
Little is known about the mechanisms involved in the production of males and females in this species with environmental sex determination. Previous reviews identifying the density of individuals as the major factor influencing sex determination were undertaken (Krueger and Oliveira, Environmental Biology of Fishes, 1999, 55, 381; Reviews in Fish Biology and Fisheries, 2005, 15, 37). Here, we review the current advances on the subject, focusing on the roles of early growth rate and interindividual relationships, which are mechanisms underpinned by density, as well as the sex differentiation process, and we question how this knowledge might influence global conservation measures.
To conclude, the management of the sex ratio in the eel population might readily become a priority for the different entities that protect eel species. Even if we do not yet understand all the mechanisms involved in eel sex determinism, we know that, likely in relation to stress and cortisol levels, aquaculture produces 90% of males.
In addition, we have to be aware of the potential role played by the initial size/energy content of glass eels on their future sex. Hence, long time stocking before release as well as late season catches should be avoided in re-stocking procedures if the ultimate goal is to increase the female production. Indeed, increasing spawner escapement by highly unbalancing sex ratio towards male production could be counterproductive.
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