Milt androgen profile and evaluation of sperm morpho-functional characteristics of wild-caught and farmed European eels (Anguilla anguilla)

Evaluating milt samples before their preservation and/or reproductive use is critical to correctly develop assisted reproductive strategies for teleost species. This is especially true in case of "critically endangered" species, like the European eel (Anguilla anguilla), whose life cycle is not closed yet, leading to the necessity of capturing younglings from natural populations for both research and productive purposes. Despite androgens being involved in spermatogenesis and playing pivotal roles in the pre-migratory morphological and physiological changes, their quantification in different biological tissues is still to be refined in European eels. The aim of this study was to evaluate the feasibility of extraction and quantification of testosterone (T) and 11-ketotestosterone (11-KT) from male European eel milts. The secondary aim was to investigate potential differences in androgens' profiles and/or functional characteristics of spermatozoa between wild-caught and farmed specimens. Twenty-four male European eels obtained from the North Adriatic region (14 wild-caught and 10 farmed) underwent a maturation-inducing hormonal treatment for milt production; blood and milt samples were then collected for androgens quantification upon ELISA and RIA methodologies. Spermatozoa were also evaluated for viability and objective motility. Plasma showed average T and 11-KT levels of 2.32 and 6.88 ng/mL, respectively, while milt 0.24 (T) and 1.09 ng/mL (11-KT). Significantly higher spermatozoa concentrations and motility were observed in farmed eels' milts. This work contributes to deepening the knowledge on teleost physiology, being the first report quantifying T and 11-KT from European eels' seminal plasma and comparing the quality of milts of farmed vs wild specimens.