Differential effects of origin and salinity rearing conditions on growth of glass eels of the American eel Anguilla rostrata: implications for stocking programmes.

In this study, growth patterns were monitored in controlled fresh and brackish water (BW) conditions for 7 months during Anguilla rostrata glass eel and elver stages. Null hypotheses tested were that there is no significant difference in growth between glass eels (1) collected from two geographic regions typified by different sex ratios, (2) reared in fresh and BW and (3) due to origin x salinity interactions. It was found that young A. rostrata from Mira River (MR, Cape Breton, Nova Scotia, Canada, an area where both males and females occur) grew faster than those from Grande-Rivière-Blanche (Québec, Canada, an area where population are highly skewed towards females; 99-100%). Anguilla rostrata from both origins also grew faster in BW, although there was a trend for origin x salinity interactions whereby this effect was more pronounced for fish from the MR. The results support the hypothesis that salinity can influence growth patterns, as possibly can quantitative genetic differences between A. rostrata glass eels from different origins. Possible explanations for these patterns and potential consequences for sex determination and translocation programmes are discussed.