Salinity tolerance in young Allis shad larvae (Alosa alosa L.)

Estuarine migration in Allis shad (Alosa alosa) usually does not take place before mid-summer, but exposure to salinity in brackish water may occur earlier as many spawning areas are of necessity located in upper estuarine zones due to the placement of dams. Therefore, Allis shad conservation programs need to consider the risk of mortality due to the ability of young Allis shad to tolerate salinity. In order to evaluate larval mortality due to the inability of larvae to withstand salinity during early ontogeny, we exposed larvae of different ages (from few days-old to 27 days-old) to salinities ranging from 0 to 30 g.l-1. Results indicate that direct seawater exposure induces high mortality in young larvae whatever the ontogenetic stage. However, young larvae can easily deal with upper estuary salinity conditions.