Abstract:Larval development of pacific cod (Gadus macrocephalus Tilesius) (0–80 dph) was observed using microscope. The experimental conditions included water temperature 2–12℃, salinity 28–32, pH 7.8–8.2, and illumination intensity 800–1200 lx. Under the micro aeration hydrostatic conditions, it was observed that on 0–5 dph (day post hatching), the yolk-sac larvae supported by complete endogenous nutrition. Specifically, on 1 dph, the pigmentation became darker and rainbow pigment appeared in the eyeball; on 5 dph, the digestive tract was cleared except for the liver; on 6 dph: the larvae started feeding, and there were small particles in the digestive tract; on 9 dph: the yolk sac was absorbed by most of the larvae and they began to feed on exogenous nutrition, in addition the rotifera in the alimentary canal and the blood circulation became visible; on 12 dph, yellow pigment became obvious in the heads of larvae; on 15 dph, colors of melanin and yellow pigment were intense, and the blubber of larvae started to form; on 17 dph, the rainbow pigment was visible in the eyes; on 20 dph, the development of eye was completed, the blood circulation could be seen in abdominal arteries, and pigment was found in the tail. During 30-50 dph, the fin ray began to develope. On 30 dph, the tail fin began to develop; on 40 dph, the larvae started feeding artemia, and the first, second, and third dorsal fins came into view; on 50 dph, the coccyx curled up, and the anal and dorsal fins were apparently visible. During 60–80 dph, the pigment cells and fin ray were further developed, and the gallbladder could be clearly observed. On 60 dph, gills were covered in red; on 70 dph, silver scales appeared on the abdomen; on 80 dph, the caps of gills were greatly developed and pelvic fins could be seen. Our observation described the developmental process of pacific cod and may provide useful data for the future large-scale artificial breeding.
