| Abstract: | Young salmonids may use substratum as hiding stations and/or shelter and they depend on invertebrates, which develop on substratum, for their feeding. For several decades, human activities have contributed to increase siltation in streams, and negative consequences on trout production have sometimes been highlighted. In the research devoted to the understanding of that negative effect, most studies have focused on embryo‐larval survival, and consequences of substrate embeddedness on later stages have rarely been investigated. In the present work we attempt at studying the impact of embeddedness on brown trout juveniles. In an experimental channel, trout growth was compared in embedded and non‐embedded sections. Growth was reduced with embeddedness due to change in trophic conditions and/or in habitat. To investigate the direct role of substratum for fish, trouts behaviour was observed from an under water observation room in two cages offering embedded and non‐embedded substrate conditions but similar trophic conditions. Competition appeared heavier in the embedded cage where dominated fishes stayed almost motionless. The effect of substratum quality on intra‐specific competition is discussed in relation with visual isolation and territory size. |
