EMBRYONIC-DEVELOPMENT OF WALLEYE POLLOCK, THERAGRA-CHALCOGRAMMA, FROM SHELIKOF STRAIT, GULF-OF-ALASKA

Eggs of walleye pollock, Theragra chalcogramma, from Shelikof Strait, Alaska, were reared at three temperatures: 3.8-degrees, 5.7-degrees, and 7.7-degrees-C. Development was divided into 21 stages. A piecewise regression model with midpoints of each stage describes the relation between time to each stage of development and temperature. Preserved eggs of each stage are described, illustrated, and photographed. Midpoint of hatch was 393 hours at 3.8-degrees-C, 303 hours at 5.7-degrees-C, and 234 hours at 7.7-degrees-C. Mean length of larvae at hatch increased linearly with temperature. We compared rate of development, time to 50% hatch, and morphological development with other studies of walleye pollock eggs. Rate of development and time to 50% hatch were similar among populations of eastern North Pacific walleye pollock. Western North Pacific walleye pollock required longer incubation times than eastern North Pacific walleye pollock. Morphological development of Shelikof Strait eggs differs from development of western North Pacific walleye pollock eggs: optic vesicles, myomeres, eye lenses, heart, and otic capsules appear earlier than in Shelikof Strait eggs, and eye pigment appears later. The differences in development may be exacerbated by the condition of the eggs in which they were examined (e.g. preserved vs. live). Developmental differences between stocks are discussed with the conclusion that model components for egg mortality and spawning biomass must be based on specimens collected in the area of interest.