Immunological and biochemical responses in asian seabass fingerlings [lates calcarifer] vaccinated with vibrio anguillarum bacterin

ABSTRACT

Groups of apparently healthy Asian seabass fingerlings [Lates calcarifer] weighing from 20 to 30 g were immunized against vibriosis by a vaccine in the form of formalin killed bacteria of Vibrio anguillarum that originated from diseased fish. This immunization was administered by three different routes which were bath immersion, orally [by feeding] or intraperitoneal injection [IP]. Immunization process was followed with booster dose by the same routes 2 weeks after the 1[st] dose. The efficacy of this vaccination was evaluated based on immune responses [specific and non specific] and protection against bacterial challenge performed by IP inoculation with 0.1 ml of bacterial, suspension of live virulent V. anguillarum at concentration of 1.2 x 108 c /ml. Antibody titres [as specific immunity], phagocytic activity phagocytic index and serum bactericidal activity [as non-specific immunity] mortality% and relative percentage survival [RPS] as challenge indicators against V. anguillarum were determined. Also, serum total protein, albumin and globulin contents and albumin / globulin ratio [A / G] were estimated. In the present study serum antibody titres, phagocytic activity and phagocytic index were significantly increased in different vaccinated groups after one and two weeks from the 1[st] dose of vaccine and after one week of booster dose of vaccine. Except, only one week after the 1[st] dose of vaccine, bath immersion vaccinated group showed no changes in serum antibody titres. Detection of serum bactericidal activity showed that there were significantly higher levels against V. anguillarum as marked reduced survive index [SI] in all vaccinated fish compared with controls at different sampling times. Serum bactericidal activity in oral and IP injection of vaccinated fish groups showed higher levels by significantly indicated reduced survive index [SI] more than in bath immersion vaccinated group at different sampling times. The vaccination conferred protection without any mortalities against V. anguillarum challenge as relative percentage survival [RPS] = 100% for each group of oral and IP injection vaccination. RPS in the bath immersion vaccinated group was 60% with 40% mortality, while, in control group there was no protection, where, RPS was zero and mortality was 100% Serum total protein and globulin contents were significantly increased in all vaccinated groups one and two weeks after 1[st] dose of vaccination and also one week after the booster dose. Albumin contents of serum were significantly decreased in bath immersion and oral vaccinated groups after one week from the 1[st] and booster doses of vaccination A / G ratios were significantly decreased in bath immersion and oral vaccinated groups after one week from the 1[st] and booster doses of vaccination also, A / G ratios in IP injection vaccinated groups were significantly decreased after two weeks and one week from the 1[st] and booster doses of vaccination respectively. Thus Asian seabass fingerlings gave good protective immune responses to Vibrio anguillarum vaccine when vaccinated by direct bath immersion orally or IP injection but in the two last routes it was better and marked protective immunity were recorded