Survival and emergence pattern of sea trout fry in substrata of different compositions

The emergence of the sea trout Salmo trutta fry of Gotland, Sweden, was studied in the laboratory. The main limiting factor fur survival up to hatching was the interstitial oxygen concentration, which depends on the gravel permeability, therefore on the substratum granulometry. Fry emergence was possible in substrata in which the geometric mean particle diameter (d(g)) was >15 mm and in substrata in which d(g) was <6 mm. In the substrata of low d(g), emergence took place earlier than in the other ones. As a consequence the fry were smaller and their yolk sac only partially resorbed. In an unfavourable environment, fry started to emerge as soon as they reacted positively to light, about 2 weeks after hatching. (C) 1998 The Fisheries Society of the British Isles.