abstract

The St. Lawrence River population of Striped Bass (Morone saxatilis), once an important resource both for commercial and recreational local fisheries, started to decline in the mid-1950s, disappeared in the late 1960s and was officially designated extirpated in 1996. A multi-agency restoration program, involving the captive propagation of wild collected fingerlings, was implemented in 2002. The goal of this program is to produce breeding groups from which will yield fingerlings to restock this depleted population. An unusually high mortality rate (reaching 20% per month) was observed during the winter of 2006 in captive fish from the 2005 cohort. Post-mortem examinations revealed extensive granulomatous coelomitis consecutive to the presence of numerous intra- coelomitic Philometra sp. In order to decrease the parasitic burden and minimize mortality, the effectiveness of different anthelminthics against Philometra sp. was evaluated. Emamectin benzoate (Slice®), at 0.05 mg/kg in feed q24h X 7d, successfully killed this nematode in 85% of the fish (n=33), whereas the administration of neither Fenbendazole (Panacur®) [25 mg/kg PO q24h X 3 or 50 mg/kg PO q7d X 2 or 2 mg/L in immersion q7d X 3 or 5 mg/L in immersion q7d X 3] nor Levamisole (Levasol®) [2 mg/L in immersion q7d X 3 or 2.5 mg/kg in feed q24h X 7d] were successful in reducing significantly the survival of Philometra sp. Preliminary results on the 2007 cohort indicate that the administration of 5 mg of emamectin per kg of pellets (equivalent to 0.05 mg/kg with a food intake of 1% bw) q24h X 7d during the fall is safe for the fish and reduces considerably the prevalence and intensity of infection by this parasite.