Eggs of the blue whiting,Micromesistius poutassouwere artificially fertilised and incubated at a range of temperatures; larvae were reared for 8½ days after hatching. The development of the eggs and early larvae is described and contrasted with previously published descriptions. The relationship between incubation temperature,t, and development time,dt, is described by the Bělehrádek equationdt=a(t‐a)b. The rate of embryonic development increased with increasing temperature, the time from fertilisation to hatching decreasing from 205 h at 6° C to 70 h at 15° C. No eggs survived to hatch at incubation temperatures above 14·5° C while at 6·2° C and below embryonic development was still proceeding when the experiment was terminated. The optimal survival rate (about 70%) was achieved between 6° and 10° C. Lengths of larvae at hatching were between 2·29 and 3·17 mm, those incubated at the higher temperatures being at a more advanced stage of ontogenetic development. The growth rate of yolk‐sac larvae declined from 10% per day immediately after hatching, to less than 1 % per day 7 days later when the yolk‐sac was fully absorbed. Egg diameter varied between 0·99 mm and 1·15 mm when fresh. During development eggs were initially bu