Debbie Blood
NOAA/AFSC, 7600 Sand Point Way N.E., Seattle, WA 98115-0070
dblood@afsc.noaa.gov
Walleye pollock (Theragra chalcogramma) eggs were obtained northwest of Unimak Island near the 100 m shelf contour on April 1, 1997. Fertilized eggs were incubated at -1, 0, 2, and 4°C, the last temperature having both a dark and diel treatment (14 hr light/10 hr dark). Egg mortality was high for the first two weeks which may have been the result of immaturity of the adult pollock; however, mortality dropped to negligible levels, leaving enough eggs to allow sampling during the incubation period and to adequately document 50% hatch in all treatments except those incubated at -1°C.
Development of embryos was normal for all temperatures except -1°C; gross abnormalities included malformation of the tail, similar to that reported by Nakatani and Maeda (1984), and the absence of eyes. The pattern of hatch was similar for all eggs incubated under constant dark conditions: 50% hatch of eggs (indicated by a diamond on each graph) occurred approximately midway through the period of time required for all eggs to hatch. However, hatching of eggs incubated under diel light was delayed; 50% hatch occurred after 90% of the hatching period had elapsed.
Nakatani, T., and T. Maeda. 1984. Thermal effect on the development of walleye pollock eggs and their upward speed to the surface. Bull. Jpn. Soc. Sci. Fish. 50(6):937-942.