ABSTRACT. The present study describes pathological changes and bacteriological findings in 'winter ulcer' in Atlantic salmon Salmo salar L. The transmissibility of the disease was also evaluated under experimental conditions. Skin changes were characterized by ulcers of varying size, and were categorized as acute to subacute, chronic, and regenerative/reparative. In the acute stages, lesions were superficial with scale loss and mild inflammation, while in the subacute stages ulcers were present that extended down to the underlying n~uscle. Histologically, the chronic stages were characterized by a severe inflammation of the dermis and of the interstitial muscle tissue. In the regeneration/reparation stages, a hyperplastic epidermis covered granulation tissue. Bacteriological investigations carried out in salmon sampled from 8 different farms with winter ulcer identified 2 groups of bacteria that were common in affected fish. The examinations performed in the present study indicate that both these groups belonged to the genus Vibrio, termed sp. 1 and sp. 2, respectively. Immunohistochemically, Vibrio sp. 1 and 2 were identified in situ associated with muscle tissue degeneration. Experimental infection with Vibno sp. 1 induced a disease similar to winter ulcer in Atlantic salmon, while inoculation with Vibrio sp. 2 had no effect. Cohabitation experiments showed that winter ulcer can be transmitted from diseased to healthy individuals, and that injection was not required to induce the process. However, mechanical skin lesions were a predisposing factor for ulcer formation. The present study provides evidence that winter ulcer is caused by an infection with a Vibrio-like bacterium, and that the disease can be transmitted through cohabitation and injection Pathological changes were not pathognomonic, and the severity of changes varied.

A rickettsia-hke organism was isolated from diseased Atlantic salmon S a h o salar in Norway. Because of morphological and serological similarities to the type strain the suggested name of the organism is Plscinckettsia salmonis. The bacteilum is considered the most probable cause of a systemic disease diagnosed in 51 farms along the west coast of Norway. Most of the cases occurred in the autumn of 1988. The disease was only recorded in smolts after exposure to sea water and cumulative mortality has been low. In 63% of fish with gross lesions examined d u n n g outbreak of disease in 14 of the affected farms, the typical macroscopic finding was a normal coloured liver with white, circular, sometimes haemorrhagic foci. Of fish with gross lesions, 35 % showed pale gllls, a yellow, mottled liver, and haemorrhages scattered throughout the skeletal muscles, perivisceral fat, the stomach wall and the swimbladder Histomorphological changes were most often observed as necrosis and granulomatous inflammation in the 11ver. Intracellular, intravacuolar bacteria-like inclusions with a n affinity for phagocytic host cells were observed Transmission electron rnicroscopy revealed individual or paired organisms enclosed in membrane-bound vacuoles.

A total of 264 bacterial strains tentatively or definitely classified as Vibrio anguillarum were examined. The strains were isolated from diseased or healthy Norwegian fish after routine autopsy. With the exception of five isolates from wild saithe (Pollachius virens), the strains originated from nine different species of farmed fish. The bacteria were subjected to morphological, physiological, and biochemical studies, numerical taxonomical analyses, serotyping by slide agglutination and enzyme-linked immunosorbent assay, DNA-plasmid profiling, and in vitro antimicrobial drug susceptibility testing. The results of the microbiological studies were correlated to anamnestic information. The bacterial strains were identified as V. anguillarum serovar 01 (n = 132), serovar 02 (n = 89), serovar 04 (n = 2), serovar 08 (n = 1), and not typeable (n = 1) as well as Vibrio spkndidus biovar I (n = 36) and biovar II (n = 1), Vibrio tubiashii (n = 1), and Vibrio fischerii (n = 1). V. anguillarum serovar 01 or 02 was isolated in 176 out of 179 cases of clinical vibriosis in Atlantic salmon (Salmo salar). V. anguillarum serovar 01 was the only serovar isolated from salmonid fish species other than Atlantic salmon, while V. anguillarum serovar 02 was isolated from all marine fish suffering from vibriosis. A 48-Mda plasmid was isolated from all V. anguillarum serovar 01 isolates examined. Serovar 02 isolates did not harbor any plasmids. Resistance against commonly used antibiotic compounds was not demonstrated among V. anguillarum isolates. Neither V. splendidus biovar I nor other V. anguillarum-related species appeared to be of clinical importance among salmonid fish. However, such bacteria were isolated from diseased turbot (Scopthalmus maximus) and sea bass (Dicentrarchus labrax). The precise role of these bacteria as fish pathogens has to be elucidated. Cell and culture morphology, cell motility, hemolysis patterns, and especially alginate-degrading ability were found to be suitable characteristics for the differentiation of V. splendidus biovar I within the arginine decarboxylase-positive group of Vibrio species. Luminescence could not be demonstrated among V. splendidus isolates. Vibriosis due to Vibrio anguillarum is one of the most important bacterial infections in fish throughout the world (1, 19). The disease has great importance, particularly for marine fish farming (4, 15, 55). Infections have been reported also among farmed bivalve mollusks and crustaceans (11, 12). V. anguillarum and closely related bacterial species are commonly found in estuarine and coastal marine habitats and can readily be isolated from different environmental sources (31-34, 52, 65, 67). These bacteria constitute part of the normal microflora of healthy marine fish (34, 41, 45). On the basis of biochemical and serological differences, two distinct biotypes of V. anguillarum were described (6, 8, 19). Biotype 2 was later differentiated as a new species, Vibrio ordalii (54). A total of 10 different 0 serovars (01 to 010) and additional 0 subgroup...

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Until recently fish welfare attracted little attention, but international and national legislation and standards of fish welfare are now emerging and an overview of these developments is presented in this study. Whereas animal welfare legislation is based on public morality, animal ethics does not automatically accept public morality as normative and elaborates arguments regarding the way humans should treat animals (referred to as moral standards). In this study we present the most common animal ethics theories. For most of these, sentience is considered a demarcation line for moral concern: if an animal is sentient, then it should be included in the moral circle, i.e. receive moral consideration in its own right and some basic welfare should be ensured. As for fish, research has revealed that the sensory system of teleosts can detect noxious stimuli, and that some kind of phenomenal consciousness, allowing the fish to feel pain, seems to be present. This raises the ethical question as to how much evidence we need in order to act on such indications of fish sentience. A simple risk analysis shows that the probability that fishes can feel pain is not negligible and that if they do indeed experience pain the consequences in terms of the number of suffering individuals are great. We conclude that farmed fish should be given the benefit of the doubt and we should make efforts that their welfare needs are met as well as possible. Finally, the way forward is briefly discussed: efforts must be made to understand what fish welfare means in practical fish farming. This will involve the development of research and education, greater accountability and transparency, compliance with and control of policies, and quality assurance schemes.