Experimental Pseudomonas anguilliseptica infection in turbot Psetta maxima (L.): a histopathological and immunohistochemical study.

Experimental infection with Pseudomonas anguilliseptica was performed both by intraperitoneal (i.p.) and bath route on juvenile turbot (Psetta maxima) in order to evaluate the pathology induced. Turbot was found to be sensitive to i.p. challenge (1.7x10(6) CFU/fish) but no to bath exposure. The i.p. challenge induced septicaemic infection and mortality. Externally, moribund fish showed distended abdomen and pale areas at day 9. The gross pathological internal signs present were abundant ascitic fluid in the peritoneal cavity, pale and enlarged spleen, pale and friable liver, and congestive and dilated gut with yellowish exudates. On histopathological examination, bacterial invasion was common in all the tissues studied but the most prominent pathological changes were observed in gut, spleen and kidney after 7 day with features of necrosis. The immunohistochemical findings support the widespread localization of the bacteria after the i.p. injection since the P. anguilliseptica was detected in spleen from day 1 post injection, in liver, kidney and gut from day 4, in muscle from day 7 and in brain from day 9. The difficulties in infecting healthy fish by bath challenge can be explained by the opportunistic nature of this pathogen.

Experimental Pseudomonas anguilliseptica infection in turbot Psetta maxima (L.): a histopathological and immunohistochemical study.

Experimental infection with Pseudomonas anguilliseptica was performed both by intraperitoneal (i.p.) and bath route on juvenile turbot (Psetta maxima) in order to evaluate the pathology induced. Turbot was found to be sensitive to i.p. challenge (1.7×106 CFU/fish) but no to bath exposure. The i.p. challenge induced septicaemic infection and mortality. Externally, moribund fish showed distended abdomen and pale areas at day 9. The gross pathological internal signs present were abundant ascitic fluid in the peritoneal cavity, pale and enlarged spleen, pale and friable liver, and congestive and dilated gut with yellowish exudates. On histopathological examination, bacterial invasion was common in all the tissues studied but the most prominent pathological changes were observed in gut, spleen and kidney after 7 day with features of necrosis. The immunohistochemical findings support the widespread localization of the bacteria after the i.p. injection since the P. anguilliseptica was detected in spleen from day 1 post injection, in liver, kidney and gut from day 4, in muscle from day 7 and in brain from day 9. The difficulties in infecting healthy fish by bath challenge can be explained by the opportunistic nature of this pathogen.

Vaccination strategies to prevent emerging diseases for Spanish aquaculture.

In recent years, three serious diseases have emerged in Spanish aquaculture. These are lactococcosis caused by Lactococcus garvieae, which is of economical importance in rainbow trout (Oncorhynchus mykiss); pseudomonadiasis caused by Pseudomonas anguilliseptica which affects gilthead seabream (Sparus aurata) and turbot (Scophthalmus maximus); and flexibacteriosis caused by Tenacibaculum maritimum which became a devastating problem in the emerging culture of sole (Solea spp). To obtain useful information for the design and development of new vaccines, antigenic characterisation of representative strains was performed. In this work we present the strategies adopted for the vaccine formulation (strains included, use of adjuvants) and administration (route, necessity of booster, etc.). The results from laboratory and/or field vaccination trials performed showed that for lactococcosis, protection lasting for five months was obtained with an oil-adjuvanted bacterin formulation. Unadjuvanted bacterin gave only a short duration of protection, which could, however, be prolonged by an antigen boost administered via the feed. A bacterin against Pseudomonas anguilliseptica gave protection for 12 weeks when tested in an experimental challenge trial in turbot. Besides the flexibacteriosis vaccine developed by our group for turbot, and due to the antigenic host-associated variability within T. maritimum, a new bacterin was developed against this bacterium to be used specifically in sole. This new bacterin, administered to sole by intraperitoneal injection, yielded RPS values of 94 % six weeks after immunization. In conclusion, these results suggest that vaccination constitutes a cost-effective method of controlling diseases that have emerged in the most important fish species being cultured in Spain.