Prevention of Ulcer Disease in Goldfish by Means of Vaccination

—A vaccine comprising cells of Aeromonas bestiarum grown in tryptic soy broth and atypical A. salmonicida cells produced in iron-limited and iron-supplemented media protected goldfish Carassius auratus when administered by immersion (dosage ø 5 3 107 cells/mL for 60 s) followed after 28 d by an oral booster (dosage 5 5 3 107 cells/g of feed), which was fed for 7 d so that each fish received about 1 g of vaccine-containing feed. After challenge by intramuscular injection of a virulent culture of atypical A. salmonicida, the relative percent survival (RPS) was more than 90%. The approach was more successful than using a commercial furunculosis vaccine with or without supplementation with A. bestiarum or atypical A. salmonicida cells. Moreover, a smooth derivative of the virulent rough culture of atypical A. salmonicida was less effective as a vaccine candidate, yielding an RPS of only 65%. Low antibody titers of 1:39–1:396 were found in the vaccinated fish. The vaccinated fish had a significantly higher proportion of dead head kidney macrophages (10.9 6 3.5%; P 5 0.0149) than did the controls (6.8 6 3.1%). However, differences in the number of erythrocytes and leukocytes, the level of phagocytic and lysozyme activities, and the proportion of lymphocytes, monocytes, and polymorphonuclear cells were not statistically significant between the two groups. The origin of vaccine development for furunculosis may be traced to the work of Duff (1942), who used an orally administered chloroform-inactivated suspension of whole cells and successfully protected cutthroat trout Oncorhynchus clarkii. Subsequent work rarely equaled or surpassed this original study (see Austin and Austin 1999). Goldfish Carassius auratus may become infected with so-called atypical Aeromonas salmonicida, which leads to the development of unsightly ulcers (Austin and Austin 1999). Often, the ulcers are populated with mixed cultures in which motile aeromonads, typically identified as A. hydrophila, are common (Austin and Austin 1999). There is a lack of evidence of synergism between bacterial groups leading to exacerbated disease, and these motile aeromonads may be secondary invaders of ulcerated tissue (Austin and Austin 1999). Previous work to develop vaccines for the control of ulcer disease of cyprinids has met with mixed success (e.g., Kozinska and Guz 2004), often because of the lack of a reproducible challenge method (Austin and Austin 1999). With the current success in salmonids of formalin-inactivated A. salmonicida preparations (e.g., Durbin et al. 1999), we considered it timely to reexamine the potential of * Corresponding author: [email protected] Received June 23, 2004; accepted September 12, 2004 Published online June 2, 2005 vaccines for controlling ulcer disease in ornamental fish.