As this footage begins, notice that there is a female and male pair. This male thinks that he has it made: he has followed this female upstream and is not lined up next to her ready to spawn. But wait a minute! An intruder, a larger redder, more handsome/fitter/studlier male suddenly shows up on the scene and squeezes himself between the femaie and male. He then bites the male, pushes him aside and them bites him again and drives him off-no genes in the next generation for him!
This footage illustrates how in the wild, the fittest male gets to spawn. In a hatchery, a person decides which genes make it to the next generation without regard to fitness
