Aims:  To study the antagonic affect of probiotic Pseudomonas M174 on the fish pathogen Flavobacterium psychrophilum. Methods and Results:  The ability of Pseudomonas M174 to inhibit the growth of Fl. psychrophilum was examined in iron‐sufficient and ‐deficient media. Possible siderophore production was also investigated. Antagonistic activity was confirmed in disease challenge experiments using a rainbow trout (Oncorhynchus mykiss) model. Adhesion of Pseudomonas M174 to fish surfaces and its ability to stimulate innate immunity was also investigated in vivo. Pseudomonas M174 antagonized Fl. psychrophilum and produced siderophores in vitro. In challenge experiments with Fl. psychrophilum, fish fed with Pseudomonas M174 had lower levels of mortalities than the controls. It was possible to find Pseudomonas M174 in the intestinal content of these fish after feeding and bathing with the probiotic, but probiotic was obtained from the gills only after feeding. Respiratory burst activity was also found to be enhanced in the M174 fed fish. Conclusions:  These results suggest that M174 is a potential probiotic against Fl. psychrophilum and has several modes of action. Significance and Impact of the Study:  Probiotics are a promising alternative to the use of antibiotics in aquaculture and could be a more sustainable disease control method.

Rainbow trout fry syndrome (RTFS) causes high mortalities during the early life stages of the fish's life cycle, partly because their adaptive immunity has not yet fully developed. Thus, immunomodulation by probiotics could be an effective prophylactic method against RTFS.

We studied the association between environmental stress and epidermal papillomatosis of roach Rutilus rutilus L. in Finnish waters using a 'matched pairs' design. Populations impacted by industrial and/or sewage effluents were compared to reference populations from pristine sites. We examined both the prevalence (proportion of diseased fish) and intensity (number of scales covered by tumors) of the disease. Results of Generalized Linear Mixed Models (GLMM) indicated that the risk of papillomatosis was 7.5 times higher in males than females, and increased 1.3 times for every 10 mm increment in fish length. We controlled for the possible effects of fish size, sex and temporal variation through sampling procedures and statistical analyses. Mean prevalence of epidermal papillomatosis was 16.6 and 5.8% in impact and reference populations, respectively (10 population pairs; n fish = 1714). Results of GLMM suggested that the risk of being diseased was 2.7 times higher in the impact than reference populations. Thus, the prevalence of epidermal papillomatosis in roach can be used as an indicator of environmental stress. Results of Linear Mixed Models indicated no difference in the intensity of the disease between impact and reference populations (5 population pairs; n fish = 73; mean ± SE 10.7 ± 1.8 and 11.7 ± 2.9 scales, respectively), although prevalence was higher in impact populations in those 5 population pairs. The possible relationship between environmental stress and intensity of epidermal papillomatosis in natural roach populations remains to be demonstrated. KEY WORDS: Environmental monitoring · Epizootic cutaneous papillomatosis · Roach · Disease · Large lakes · Matched pairs Resale or republication not permitted without written consent of the publisherDis Aquat Org 72: [1][2][3][4][5][6][7][8] 2006 and by isolation from cell culture (Schwanz-Pfitzner 1976, Bloch et al. 1986, Sano et al. 1993. However, induction of papillomas can possibly also take place without viral infection (e.g. Grizzle et al. 1984, Smith et al. 1989a). Thus, the connection between papillomatosis and environmental stress can be produced both by the stress induced impairment of the immune system of fishes and by direct carcinogenic effects of contaminants (Sano et al. 1991, 1993Lee & Whitfield 1992, Baumann et al. 1996.In the North American Great Lakes, epidermal papillomatosis has been proposed as a bioindicator of contaminated waters (Munkittrick & Dixon 1989, Baumann 1992, Premdas et al. 1995, Baumann et al. 1996. The International Council for the Exploration of the Sea (ICES) has adopted epidermal papillomatosis in dab Limanda limanda as an indicator of environmental changes in the North Atlantic coastal areas (Bucke et al. 1996). Because new tools are required by the European Union's Water Framework Directive for determining the ecological status of lakes, we investigated the possible use of the roach-papillomatosis system in monitoring of environmental stress in Finnish waters.In contrast to prevalence, the intensity of ...

Studies of epidermal papillomatosis in fish populations have only rarely focused on the intensity of the disease, i.e. the number and size of papillomas. Furthermore, the methods used to evaluate the intensity of papillomatosis have not been standardized. We tested the reliability of a method based on counting of scales covered by papilloma tumours in roach, Rutilus rutilus (L). In addition, we studied the frequency distributions of the number of scales covered by papillomas within populations, evaluated the correlation between the prevalence and mean intensity of the disease among populations and examined the intensity of papillomatosis in roach with respect to sex and size of fish. Reliability of the scale coverage method was high. Therefore, the method could offer an effective way to determine the intensity of papillomatosis in fish species with large scales. The frequency distribution of the scale coverage of papillomas was highly aggregated within all populations studied. The mean intensity of papillomatosis increased with the size of the fish and was higher in males than in females. However, there was no correlation between the mean intensity and prevalence of the disease among the 19 roach populations studied.