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This paper examines aspcets of the resistance of Aeromonas salmonicida isolates to the major fish farming antimicrobials. The antimicrobial resistance of an extensive chronological series of isolates appears to reflect the changing use of different compounds in tish farming since 1969. Repetitive challenge by 5(1% MIC concentrations of 4-quinolonc antimicrobials against selective isolation of viable colonies resulted in a 7 2 x increase in resistance in 12 generations, demonstrating the likely outcome of drug misuse.

The devciopment of a selective-differential medium (ROD) for the isolation of Yersinia ruckeri from earrier and elinieally infected rainbow trout, Oncorhynchus mykiss (Walbaum), is described. This medium was a useful aid for the detection of Y. ruckeri in faecal material and allowed the epidemiology of enteric redmouth disease to be studied in greater detail. Regular use of ROD at two fish farms in southern England has demonstrated that isolation of Y. ruckeri from faeces was possible under field eonditions up to 4-6 weeks before acute elinical kidney infection oeeurred.

Aims: To determine the prevalence of total and pathogenic Vibrio parahaemolyticus (Vp) and V. vulnificus (Vv) in blue crabs, water and sediment from the Maryland Coastal Bays (MCBs), USA. Methods and Results: Crab, haemolymph, sediment and seawater samples were collected monthly from four sites in MCBs from February 2012 through October 2012 with environmental parameters recorded. The most-probablenumber (MPN) methodology was used to enumerate Vp and Vv with presumptive colonies and the presence of virulence markers confirmed using polymerase chain reaction (PCR). Results indicate that blue crabs contained both Vp and Vv at densities (7Á28 and 5Á43 log MPN g À1 , respectively) higher than those reported for bivalves. In addition, markers for clinically relevant strains of both species were detected in over 30% of samples. Haemolymph, sediment and seawater samples were also routinely positive for both species and clinically relevant strains, but generally at lower densities than found in crabs (4Á27, 3Á28, and 2Á39 log MPN g À1 per ml À1 Vp, and 4Á28, 2Á49 and 2Á38 log MPN g À1 per ml À1 Vv). Conclusions: Blue crabs concentrate Vp and Vv at levels greater than found in water or sediment. While changes in abundance associated with temperature are apparent, there is little evidence to support differences among sampling locations. Significance and Impact of the Study: These results highlight the potential for blue crab related vibriosis and the importance of proper handling, cooking and care of this popular seafood before consumption. IntroductionBlue crabs (Callinectes sapidus) exist along the western border of the Atlantic Ocean from the Canadian province, Nova Scotia down to Argentina (Reichmuth et al. 2009). They are of ecological and economic importance and require an estuarine environment such as the Chesapeake Bay and the Maryland Coastal Bays (MCBs) for growth.Ecologically, blue crabs perform many roles in the estuarine food web depending upon life stage (Reichmuth et al. 2009). Blue crabs are also a very popular delicacy in the US Gulf of Mexico and Atlantic coastal areas. In 2011, the Chesapeake Bay crab fishery had a total harvest of 67Á3 million pounds. According to the 2012 annual winter dredge survey completed by the Maryland Department of Natural Resources, the blue crab population had increased 66% to 764 million. This

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A comprehensive bacteriophage typing scheme for Aeromonas salmonicida, the causal agent of furunculosis in fish, is described. It distinguishes 27 bacterial groups based on sensitivity patterns to 18 bacteriophage isolates. In addition, the sensitivity patterns are shown to reflect the morphological characteristics of the host bacterium. The 'rough', 'smooth' and 'G-phase' forms possess different quantities of lipopolysaccharide in the cell wall and this influences bacteriophage attachment. The problems related to these morphological variations are discussed.

This immersion vaccination study used rainbow trout Salmo gairdneri and compared the efficacy of a vaccine alone with one containing liposome particles against a natural challenge of fish furunculosis. Results indicated that fry could be protected with a 3-component vaccine consisting of whole cells, 'toxoided' extracellular products, and lipopolysaccharide and that the protection level was significantly enhanced when the vaccine also contained liposomes. In addition, vaccinated fish appeared to be significantly larger than control fish.

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