National Fish Disease Laboratory (NAFUS)

Centre for Fish and Wildlife Health (FIWI)

Could a climate change influence PKD in wild fish populations?

Thomas Wahli, Daniel Bernet, Helmut Segner, Heike Schmidt-Posthaus

TW/08

TW/2009

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

TW/2009

Effect of temperature in the laboratory

Effect of temperature on proliferation of T. bryosalmonae in kidney of trout

Differences in maximal values and time of maximal valuesDifferences limited to first phase of infection

Bettge et al. 2009

*

0 5 12 19 26 33 40 47

**107

106

105

104

103

102

101

Num

ber o

f par

asite

DN

A c

opie

s

0 5 12 19 26 33 40 47 75 days p.i.

12°C18°C

TW/2009

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

TW/2009

Effect of temperature in the laboratory

Temperature 12°C 14°C 16°C 18°C

Prevalence 100% 100% 100% 100%

Cum. mort. 5.6% 37.7% 45.5% 85%

Maximal value of parasite DNA

a

bb

b

Bettge et al. 2009

TW/2009

Effect of temperature in river

Schubiger 2004

TW/2009

Results from projects

Negative sitePositive site

From 2000 to 2006 more than 7000 fish (mostly “brown trout of the year“) investigated for the presence of T. bryosalmonae

Rivers Sites

Total 217 285

Posi-tive

95 (43.8%)

130 (45.6%)

So far never infected fish in lakes

In 6 out of 65 (9.3%) fish farms infected fish

Wahli et al. 2002, 2007

TW/2009

n sites

Influence of temperature on geographic distribution

Frequency of sampling sites with PKD positive fish, stratified by altitude of the sampling sites (grouped in 100 m classes).

Wahli et al. 2008

TW/2009

Influence of temperature on geographic distribution

Distribution of PKD in Switzerland according to altitude

Site with infected fishSite without infected fish

Meter above sea level

LakeBorder of canton

TW/2009

rs = -0.18

Influence of temperature on prevalence

Wahli et al. 2008

TW/2009

Influence of temperature on infection intensity

Wahli et al. 2008

rs = -0.18

Infection intensity (Score from 0 to 6)

TW/2009

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

TW/2009

Decrease in brown trout catches

Nowak et al. 1997 complemented with PKD data

TW/2009

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!