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Fishery Bulletin 92(2). 1994 



where age of the egg is expressed in hours. The 

 value of R 2 is 0.96 for component 1 and 0.99 for 

 component 2. 



We compared our rates of egg development to 

 other walleye pollock incubation studies in the 5- 

 7°C range (Table 4). There was a significant differ- 

 ence between regression equations of incubation 

 time to 50% hatch and temperature for western 

 versus eastern North Pacific studies (P<0.01), but 

 the slopes were not different (P=0.18). Based on the 

 95% confidence interval about the parameter esti- 

 mates, time to 50% hatch of western North Pacific 

 walleye pollock tended to be 1.2 to 1.3 times longer 

 on average than that of the eastern North Pacific 

 fish at a specific temperature. 



Morphological descriptions 



Walleye pollock eggs are pelagic and have a smooth, 

 clear chorion and homogeneous yolk. No oil globules 

 are present. Preserved eggs range from 1.2 to 1.8 

 mm in diameter, although most are 1.35-1.45 mm 

 (Matarese et al., 1989). Appearance of the egg var- 

 ies with type of preservative. There was little or no 

 shrinkage of yolk material in Stockard's solution, 



whereas yolk of formalin-preserved eggs decreased 

 in volume and the yolk membrane frequently col- 

 lapsed. This effect of formalin preservation was 

 helpful in determining how much of the tail had 

 lifted away from the yolk in late-stage embryos. 



Development of walleye pollock eggs and embryos, 

 from fertilization to just before hatching, was di- 

 vided into the following 21 stages (Table 2): 



Precell (stage 1) Cytoplasm at the animal pole 

 forms a blastodisc; bands of cytoplasm extend from 

 below the equator to the blastodisc (Fig. 5A), which 

 is without distinct margins (Fig. 6A). When intact, 

 the yolk membrane almost touches the inner wall 

 of the chorion. The perivitelline space is most vis- 

 ible over the blastodisc. 



2 cells (stage 2) The first cell division of the 

 blastodisc is in the horizontal plane. Cell material 

 may not be equally divided (Figs. 5B and 6B). 



4 cells (stage 3) The second cleavage is perpen- 

 dicular to, and in the same plane as, the first. Cells 

 are roughly equal in size and form a square (Figs. 

 5C and 6C). 



8 cells (stage 4) The third cleavage is perpen- 

 dicular to the second cleavage (parallel to first cleav- 

 age). Each cell divides in half in the horizontal 



