Development in Salmo trutta at different temperatures, with a quantitativescoring method for intraspecific comparisons

The period from fertilization to the end of yolk resorption in the brown tr out Salmo trutta was described as a series of 40 successive steps, each des cribing the maturation of multiple characters during an interval of develop ment. An associated quantitative scoring system was devised, whereby indivi dual embryos were assigned points ranging from 1 to 1000, on the basis of t he assessment of a wide range of developmental features. Developmental scor e increased linearly with embryonic age at all temperatures studied (2, 6 a nd 10 degrees C), indicating that the relative durations of successive inte rvals of development were maintained. At lower temperatures, the beginning of heartbeat, trunk muscle contractions, bile production, pectoral fin move ments and hatching were all delayed relative to the rest of development. Th erefore these features have been excluded from the scoring system. Maternal migratory type did not affect early developmental patterns. (C) 1999 The F isheries Society of the British Isles.