Light sensitivity and substrate penetration by eleutheroembryos of brook (Salvelinus fontinalis) and lake charr (Salvelinus namaycush) and their F1 hybrid, splake.

Critical light levels necessary to produce avoidance movements in photonegative free embryos (eleutheroembryos) of the lake and brook charr and their F1 hybrid splake, (S. namaycush X S. fontinalis) were determined and compared to previously studied movement patterns within artificial substrate systems. Light sensitivity was inversely related to depth of penetration into artificial substrates. As well, brook charr held in vertical profile tanks under either 14 : 10 h light : dark cycles or total darkness showed similar movement patterns. These results do not support previous hypotheses concerning the role of ambient light in the initial downward movement of eleutheroembryonic salmonids within spawning redds.