Influence of incubation temperature on body movements of Atlantic cod (Gadus morhua L.) embryos and on size at hatch

Body movements of cod (Gadus morhua L.) embryos reared from fertilization to hatch at 5.4°C were observed at various stages of development and at six experimental temperatures ranging from 0–10°C. Frequency of cod embryo body movements increased from zero at 42 degree-days post fertilization to maximal at 73–82 degree-days (1 or 2 days prior to hatch). Embryos were most active at 2°C (mean of 5.5 movements per 10 min), with activity declining to less than 1/10 min at 8–10°C. Lengths of hatched cod larvae reared at a series of constant temperatures (from 4–10°C) from fertilization to hatch were greater at lower incubation temperatures. Incubation temperatures of 2–4°C were found to be optimal for incubation of cod eggs.