Thermal dependence of embryonic growth and development in brown trout

Fertilized eggs from a brown trout Salmo trutta population in northern Spain were incubated in the laboratory at 4, 6, 8, 10, 12, 14, 16 and 18degrees C. Developmental stage and embryo size were monitored by taking samples at regular intervals. Survival was maximal at 8 and 10degrees C and decreased at higher and lower temperatures. Despite starting development, no embryo hatched at 16 and 18degrees C, which suggests an upper thermal limit for development between 14 and 16degrees C. Time required to reach a given ontogenetic stage decreased with increasing temperature. Embryos incubated at lower temperatures were larger at 50% hatching, and these differences.. persisted throughout the subsequent embryonic period until the start of exogenous feeding. A comparison with previously published data indicates low interpopulation variability in thermal sensitivity of embryonic development, even in consideration of the great latitudinal range of the studies. (C) 2003 The Fisheries Society of the British Isles.