Spawning migration of brown trout, Salmo trutta in the Moravka reservoir

The spawning migration from Moravka reservoir to the Moravka river tributary of brown trout in autumn (October - November) lasted 22, 24, and 27 days respectively in the seasons 2002-2004. In 2002, 187 fish were trapped, while the number of trapped spawners increased to 447 in 2003 and 2230 in 2004. Spawning males were significantly longer than females (P<0.01). In 2002, more females than males (P<0.05) migrated. The sex-ratio in the following seasons did not significantly differ from 1:1. Spawning migration started under the conditions of increasing water levels and the water temperature decreased below WC in the reservoir. The peak of spawning, in all three seasons, took place between 28 October and 3 November, and the river water temperature varied from 6 to 8 degrees C. The spawning in 2002 was more nocturnal (between 8:00 p.m. to 6:00 a.m.) than diurnal (P<0.01) and the diel activity showed the multimodal distribution. There were no large or significant differences between the diurnal and nocturnal migrations in 2003 and 2004. Single environmental variables and their interaction were significantly related to the spawning migration only in 2003 and 2004 (P<0.001).