The effect of low temperatures on the early development of zebrafish embryos. (a,b) 30 min incubation of fertilized eggs in 4 °C causes developmental defects and increased mortality while the environmental temperature of 12 °C is better tolerated causing only moderate defects and mortality after 2 h incubation. Newly fertilized eggs were kept in E3 water at 4 °C or 12 °C for 30 min, 1 h or 2 h after which they were moved to 28 °C. The survival and well-being of the embryos was followed for 24 h and compared to control embryos kept in 28 °C throughout the experiment. Figures represent combined results from 3 independent experiments. n(control) = 353, n(30 min/4 °C) = 278, n(1 h/4 °C) = 335, n(2 h/4 °C) = 247, n(30 min/12 °C) = 384, n(1 h/12 °C) = 396, n(2 h/12 °C) = 323. (c) The comparative developmental stages of the control (E3 treated) and the cold treated embryos. Newly fertilized eggs were kept in 12 °C for 30 or 60 min and the development was followed by time-lapse imaging. (d) The times for the first, the second and the third cell division in cold treated (12 °C) and control (E3 treated) embryos. Time-lapse experiments were repeated twice. Error bars represent SD, *p < 0.05, **p < 0.01, ***p < 0.001).
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