National Fish Disease Laboratory ( NAFUS) Centre for Fish and Wildlife Health ( FIWI)

1. Could a climate change influence PKD in wild fish populations? Thomas Wahli, Daniel Bernet, Helmut Segner, Heike Schmidt-Posthaus National FishDisease Laboratory (NAFUS) CentreforFishandWildlifeHealth (FIWI) TW/08

2. Temperature related effects in PKD • Investigation of effects with regard to: • Number of parasites in fish • Expression of pathological lesions • Cumulative mortality • Geographical distribution of infected fish

3. Effect of temperature in the laboratory Effect of temperature on proliferation of T. bryosalmonae in kidney of trout * 107 106 105 104 103 102 101 * * Number of parasite DNA copies 12°C 18°C 0 5 12 19 26 33 40 47 75 days p.i. 0 5 12 19 26 33 40 47 Differences in maximal values and time of maximal values Differences limited to first phase of infection Bettge et al. 2009

4. Effect of temperature in the laboratory • Effect of temperature on degree of histological alterations in kidney of trout infected by T. bryosalmonae: • Alterations at 18°C earlier visible than at 12°C • Alterations slightly more pronounced at 18°C than at 12°C • Maximal alteration intensity reached earlier at 18°C • Full recovery earlier at 18°C General finding on effect of temperature on development of organ alterations: No difference in quality of alterations but in quantity and development over time

5. Effect of temperature in the laboratory b b b a Bettge et al. 2009

6. Effect of temperature in river Schubiger 2004

7. Results from projects From 2000 to 2006 more than 7000 fish (mostly “brown trout of the year“) investigated for the presence of T. bryosalmonae In 6 out of 65 (9.3%) fish farms infected fish Negative site Positive site So far never infected fish in lakes Wahli et al. 2002, 2007

8. Influence of temperature on geographic distribution n sites Frequency of sampling sites with PKD positive fish, stratified by altitude of the sampling sites (grouped in 100 m classes). Wahli et al. 2008

9. Influence of temperature on geographic distribution Distribution of PKD in Switzerland according to altitude Site with infected fish Site without infected fish Lake Border of canton Meter above sea level

10. Influence of temperature on prevalence rs = -0.18 Wahli et al. 2008

11. Influence of temperature on infection intensity rs = -0.18 Infection intensity (Score from 0 to 6) Wahli et al. 2008

12. Water temperature and population density Decrease in brown trout catches since the 1980ies in relation to altitude of rivers • Decrease most pronounced in rivers located at altitudes between 200 and 400 m. a. s. l. • No or only minimal decrease of catches in rivers located above 800 m. a. s. l. (Data from Hari et al. 2006) • Data indicative for a relation between decrease and altitude of rivers • Rivers with most marked decreases in areas with demonstrated presence of T. bryosalmonae infected fish

13. Decrease in brown trout catches Nowak et al. 1997 complemented with PKD data

14. Concluding remarks • Temperature data over time available • Data on effect of temperature on parasite number in fish, degree of alterations and mortality rates available • Data on geographical distribution of T. bryosalmonae infected fish available • Different sets of data allow to draw conclusions on possible temperature effect on development of brown trout populations • Further increasing temperatures might lead to upward shift of presence of T. bryosalmonae infected fish and further decreasing brown trout populations -> to be followed!