Long-term data from underwater video recordings in the wild and in semi-natural channels are used to describe and compare the reproductive behaviour of fishes in the Salmoninae subfamily. The thesis is divided into five chapters. In the first, a new division of male alternative strategies and tactics based on relative age at maturation (strategy) and on behaviour in the spawning grounds (tactic) is proposed. A variation to the evolutionarily stable strategies (ESS) model based on a growth velocity-dependent maturation threshold is suggested.

In the second chapter, methods of video recording and analyzing behaviour during spawning are introduced. The reproductive behaviour in the Salmoninae is described dividing it into different phases related to female nest selection, construction, and completion.

In the third chapter, the role of instincts during spawning, as well as the mechanisms by which they are released, are explained based on internal motivation and external stimuli. Data are used to propose false spawnings in females should be regarded as low intensity behaviour and that male digging represents two different types of displacement reaction with threatening and courting functions as ultimate causes.

In the fourth chapter, observations on different species are used to open a theoretical discussion about the role of female choice in salmonines. Particularly, the importance of Zahavi’s principle among the different breeding patterns is contrasted with Fisherian runaway selection. A combination of both mechanisms is suggested. Special attention is given to male’ quivering behaviour. Different hypotheses are proposed to explain its origin and function.

Chapter 5 uses data from underwater video recordings to construct the phylogeny of Oncorhynchus and Salvelinus based only on behavioural traits during spawning. A maximum parsimony analysis using Thymallus, Hucho and Salmo as outgroups is conducted (PAUP* 4.0 b10). The results agree with some minor differences our current understanding of these two genera based on morphological and molecular data. The possible evolution of several characters is discussed in detail.

Throughout the manuscript still underwater video frames are used to illustrate the explanations.