Immune deficiency causes annual late summer brown trout (Salmo trutta) mortality in Austrian prealpine river systems
- 122 Downloads
For several years, severe brown trout (Salmo trutta) mortality has been observed in different prealpine river systems of Austria, Southern Germany, and Switzerland during late summer and early autumn. Often, the skin of the effected fish shows a medium to intense black pigmentation, and therefore this phenomenon is called “Schwarze Bachforelle Phänomen” or “proliferative darkening syndrom”. The present study was conducted to gain insight about its presence. From middle of May to end of August, brown trout and rainbow trout were kept in experimental tanks supplied with water from an effected river system. In brown trout, samples for blood diagnostics and histological investigations were taken after 0, 47, 62, and 77 days, and in rainbow trout after 0 and 107 days. Brown trout from a wild population were investigated for comparative purposes. Brown trout showed no abnormalities till the end of June. All fish sampled in the second half of July suffered from severe immune deficiency as the numbers of peripheral blood granulocytes and lymphocytes, plasma lysozyme activity, and plasma immunoglobulin levels significantly decreased. During August, the number of erythrocytes decreased and the osmotic fragility of the erythrocytes increased. Senescent erythrocytes became more frequent and the hematopoietic tissue of spleen and kidney enlarged. Also, the cellular composition of the spleen changed as the number of hemoblasts and normal erythroblasts decreased while the number of atypical erythroblasts increased. In the pronephros and hematopoietic tissue of the mesonephros, aggregation of macrophages and tissue disintegration was frequently observed. This was similar for brown trout from the field experiment and from the wild population. High mortality occurred in the end of July and during August. Death of the fishes might have been caused by secondary infections with microorganisms. Almost similar changes were observed in rainbow trout, however, the mortality was lower.
KeywordsBrown trout Rainbow trout Mortality Immunity Lymphocytes Granulocytes Immunoglobulin Lysozyme
The project was funded by the “Oberösterreicher Landesfischereiverband” and by the “Amt der Oberösterreichischen Landesregierung”. We are grateful to Dipl. Ing. Stefan Keil, the head of the sewage plant of Bad Ischl and to his team for the generous support and help in our field studies. Support also came from the fish farm of Kreuzstein and from Mr. Alfred Ungar in providing material.
- Born O, Schwaiger J (2003) Bachforellensterben in Bayern. Schriftenreihe des Landes-fischeiverbandes Bayern 9Google Scholar
- Busse HJ, Glöckner J, Haunschmid R (2005) Identification of bacteria causing bacteremia in brown brout. Congress of Bacteriology and Applied Microbiology, San Francisco, USAGoogle Scholar
- Ellis AE (1990) Lysozyme assays. In: van Muiswinkel WB (ed) Techniques in fish immunology. SOS Publications, Fair Haven, pp 101–103Google Scholar
- Feuerstein G (2004) Bachforellensterben: Allgemeine Betrachtungen zum Problem und neueste Erkenntnisse vom Expositionsversuch in Wartau (SG). http://s.o.w.tripod.com/bachforellensterben.htm
- Moser R (2000) Mysteriöses Bachforellensterben 1997 und 1999. Mitgliederzeitschrift des Sportanglerbundes Vöcklabruck 3:4Google Scholar
- Press CM (1998) Immunology of fishes. In: Pastoret PP, Griebel P, Bazin H, Govaerts A (eds) Handbook of vertebrate immunology. Academic Press, London, pp 3–62Google Scholar
- Schwaiger J, Gerst M, Römer C, Ferling H (2006) Studie zum Auftreten des Bachforellensterbens im Mühlbach, Kanton St. Gallen, Schweiz. Final report 2006Google Scholar
- Siwicki AK, Anderson DP (1993) Nonspecific defense mechanisms assay in fish. II. Potential killing activity of neutrophils and macrophages, lysozyme activity in serum and organs and total immunoglobulin (T-Ig) levels in serum. Fish diseases diagnosis and prevention’s methods. FAO-Project GCP/INT/526/JPN, IFI Olsztyn: 105–112Google Scholar