ACCLIMATION TRIALS OF WILD AND HATCHERY SEA BASS (DICENTRARCHUS-LABRAX) FRY AT DIFFERENT SALINITIES

Hatchery and wild sea bass (Dicentrarchus labrax) fry were transferred from sea water to low salinities and freshwater (FW) using three diff erent operational protocols: 1) direct exposure to low salinities and FW (LC 50 test, ST 50 test); 2) quick acclimation to FW (48h); 3) slow acclimation to FW (17d). Direct exposure to freshwater led to the dea th of all fry. Complete survival was observed after direct transfer to salinities greater-than-or-equal-to 9 ppt, both in wild and hatchery fry. Hatchery fry tolerate direct transfer to low salinities (LC 50 = 4.393 ppt) better than wild fry (LC 50 = 3.215 ppt). Slow acclimation protocol leads to higher survival rates (nearly 90 %) than does the qu ick procedure. In 48h and 17d acclimation trials wild fry tolerate FW better than hatchery fry. Hypotheses to explain observed differences i n wild hatchery tolerances to low salinities and FW are discussed.