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Keywords:

  • egg-ribbon;
  • Perca fluviatilis L;
  • spawning;
  • temperature

The effects of water temperature on the timing of spawning of perch Perca fluviatilis in Lake Geneva were assessed in a 20 year survey (1984–2003). Spawning started at the end of April or at the beginning of May, when the water temperature rose to >10° C, but most of the spawns were laid when water temperature exceeded 12° C. This led to a positive correlation between the date of the mid-spawning period and the date when the water temperature rose to >12° C. Large perch had a tendency to spawn later than the small ones, which led to a positive correlation between the date of mid-spawning period and the yearly mean width of perch egg-ribbons. The coefficient of multiple determination between the date of mid-spawning period and the mean width of the ribbon of spawn, combined with the date when the water temperature rose to >12° C was r2= 0·77. The perch generally chose deeper spawning places (12 m) at the end of the spawning period than at the beginning (4 m), which was related to water temperature.