Vaccination trials of sea bass (Dicentrarchus labrax) against pasteurellosis using oral, intraperitoneal and immersion methods.

Photobacterium damsela subsp. piscicida (Phdp) is the aetiological agent of fish pasteurellosis, causing heavy losses in intensive mariculture plants. The present work compares the protective efficacy of five different vaccine formulation: oral, intraperitoneal, immersion, bivalent immersion (Vibrio anguillarum) and immersion associated with immunostimulants. Each of these vaccine formulations containing whole cells of Phdp formalin inactivated (FKC), was administered to 100 sea bass weighing approximately 2 g; 100 non-vaccinated sea bass were used as controls. Protection against pasteurellosis was tested for 40 days after vaccination by intraperitoneal challenge: each fish was inoculated with Phdp cells at a concentration of 2.75 x 10(4) cfu/ml. Mortality was recorded over the following 14 days, vaccine protection was evaluated using a relative percentage survival (RPS) index. The intraperitoneal formulation gave excellent protection (RPS 82.4%). The most effective immersion form was that followed by simple immersion (RPS 23.1%) followed by the group vaccinated with bivalent vaccine (RPS 18.7%). Protection conferred orally (RPS 28.6%) is of interest for practical purposes.