Salinity effects on anguillicolosis in Atlantic eels: a natural tool for disease control

Anguillicolosis, the disease caused by the invasive nematode Anguillicoloides crassus, is one of the many threats facing the already endangered Atlantic eel species. We conducted a systematic review of literature data linking water salinity and prevalence of the infection during the continental phase of Anguilla anguilla and A. rostrata. Overall, we showed a significant negative relationship across all sites (r(S) = -0.42, n = 77). In order to limit the effect of confounding factors (e. g. variable latitudes and parasite introduction dates), we performed a meta-analysis on the correlation coefficients calculated from data within studies (restricted period and area) and revealed a stronger negative relationship (-(r) over bar = -0.75, n = 13). Finally, using our long-term monitoring in a French Mediterranean lagoon, we documented a step decrease in both parasite prevalence and induced swimbladder pathologies in response to increased salinity values. Salinity effects manifested with an apparent threshold value around 15% and are readily appreciable in young-of-the-year eels. To date, managing around water salinity parameters remains one of the best options to control the ever-expanding infection (both in aquaculture and in the wild) and to improve the quality of future spawners en route to the Sargasso Sea.