M74 in salmon from different rivers

Annual incidence of M74 in salmon from the Tornionjoki, Simojoki, Kemijoki and Kymijoki rivers

Female-specific incubation of eggs was started with the salmon spawners that ascended the Simojoki river in autumn 1985. Eggs for experimental incubation have been obtained from ascended spawners caught for governmental fish hatcheries. Eggs are incubated in the hatcheries and/or in the laboratory. The mortality of yolk-sac fry is observed from hatching until the end of the yolk-sac phase. (The explanations of the figure are given below.)

The eggs of salmon from the Tornionjoki river have been in experimental incubation from 1987 onwards except for a couple of years. (The explanations of the figure are given below.)

Female-specific incubation of salmon from the Kymijoki river was started in 1994.

Female-specific incubation of salmon from the Kemijoki river was started in 2005.

Explanations of the figures:

The year in the graphs is the spawning / hatching year.
The numbers of females or egg batches in experimental incubation are given in parentheses below the date axes.
YSFM = the mean annual yolk-sac fry mortality rate of all females;the vertical line indicates the standard error of the mean.
M74FEMALES = the proportion (%) of those females whose offspring have shown M74 symptoms.
FEMALES100% = the proportion (%) of those females whose offspring have all died.

The mortality rate of eggs from Tenojoki river salmon (Atlantic salmon), incubated as a comparison, has normally been below 10%.

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