Yusa (1954). Yusa described the development of 

 walleye pollock embryos incubated at 6°-7°C. We 

 classified Yusa's developmental data according to 

 the stages of our Table 1 and calculated age (in hours) 

 at 6.5°C to the midpoints of Stages II- VII. Rates of 

 development of walleye pollock embryos were 

 similar (Table 6) for both studies. 



Our study was not designed to determine hatching 

 time of individual walleye pollock embryos. Although 

 we recorded the presence of larvae in culture vessels, 

 we did not monitor distribution of hatching times. 



A preliminary estimate of hours to hatching, 

 however, can be derived using the midpoint age of the 

 observed hatching interval, y, and the empirically 

 derived Equation (1): 



lny = 



1 



a + bT 



(2) 



where least square estimates of a and b are a — 

 0.15012, b = 0.00431, and T= water temperature 

 (°C). The estimated hours to midpoint of hatching 

 using Equation (2) are similar to the observed mid- 

 point ages at hatching (Table 7). 



Conclusions 



In general, walleye pollock embryos developed 

 more rapidly at higher temperatures, as indicated by 

 shorter time intervals between stages at higher tem- 

 peratures (Fig. 1). Rates of embryonic development 

 at the temperatures used in our study were 

 significantly different from each other; however, the 

 rates were similarly related to temperature regard- 

 less of stage of development (Fig. 3). 



The age (in hours from fertilization) of a walleye 

 pollock embryo at any stage of development (Table 

 1) can be estimated from the mean incubation tem- 



Table 6.— Age (time from fertilization, in hours) of 

 walleye pollock embryos at 6.5°C to midpoints of develop- 

 ment for Stages ll-VII. Data from Yusa (1954) and this 

 study. 



TABLE 7. — Predicted and observed hours to hatch- 

 ing of walleye pollock embryos at temperatures of 

 2° > 5 ,6 ,8 ) andll C. 



6 



8° 



11 c 



Predicted hours 

 Observed hours 

 Hours difference 



544 

 555 

 + 11 



338 

 333 



-5 



294 



285 



-9 



225 158 



232 158 



+7 



perature by 1) determining the temperature- 

 dependent coefficients in Table 5 and then 2) solving 

 the generalized predictive Equation (1). Together, 

 these equations describe the relationship between 

 age, stage of development, and temperature for 

 walleye pollock at easily identifiable stages (Table 1) 

 for temperatures within the range 2°-ll°C. 

 Simulated temperature fluctuations had no measur- 

 able effect on the accuracy of the generalized predic- 

 tive equation; therefore, an estimate of the age of an 

 embryo based on mean temperature apparently has 

 the same reliability as an estimate based on a con- 

 stant temperature. Although not as accurate as the 

 equations, the contour plot (Fig. 3) can also be used 

 to approximate the age (time from fertilization, in 

 hours) of an embryo given a mean incubation tem- 

 perature and stage of embryonic development. At 

 6.5°C, rates of development of walleye pollock em- 

 bryos from Alaskan and Japanese waters are 

 similar. 



Acknowledgment 



We thank Ken Krieger, Auke Bay Biological 

 Laboratory, Auke Bay, Alaska, for constructing and 

 maintaining the laboratory facilities used in this 

 study. 



Literature Cited 



Box, G. E. P. 



1950. Problems in the analysis of growth and wear curves. 

 Biometrics 6:362-389. 

 Ferraro, S. P. 



1980. Embryonic development of Atlantic menhaden, 

 Brevoortia tyrannus, and a fish embryo age estimation 

 method. Fish. Bull. U.S. 77:943-949. 

 Hamai, L, K. K. Kyushin, and T. Kinoshita. 



1971. Effect of temperature on the body form and mortality 

 in the developmental and early larval stages of the Alaska 

 pollack, Theragra chalcogramma (Pallas). Bull. Fac. 

 Fish., Hokkaido Univ. 22:11-29. 

 KlNNE, O. 



1977. Cultivation. In Marine ecology, a comprehensive, in- 

 tegrated treatise on life in oceans and coastal waters, Vol. 

 HI, part 2, 1293 p. John Wiley & Sons, N.Y. 

 Morrison, D. F. 



1967. Multivariate Statistical Methods. McGraw-Hill, N.Y., 

 338 p. 

 Yusa, T. 



1954. On the normal development of the fish, Theragra 

 chalcogramma (Pallas), Alaska Pollack. Bull. Hokkaido 

 Reg. Fish. Res. Lab. 10:1-15. 



Evan B. Haynes 

 Steve E. Ignell 



Northwest and Alaska Fisheries Center 



Auke Bay Laboratory 

 National Marine Fisheries Service, NOAA 

 P.O. Box 155, Auke Bay, AK 99821 



894 



