FERRARO; EMBRYONIC DEVELOPMENT OF ATLANTIC MENHADEN 



Brevoortia tyrannus embryos used in the exper- 

 iments were fertilized and reared at 20.5° C and 

 23.5%o for the first 5 h of embryogenesis. To adjust 

 development data for the delay in attaining ex- 

 perimental temperatures, correction factors were 

 calculated to estimate the age embryos would 

 have been at the beginning of the experiment had 

 the embryos been incubated at experimental 

 temperatures from fertilization. Since at 20°±0.5° 

 C incubation temperature was constant through- 

 out development, the correction factor used was 

 the ratio of development time to stage 9 for em- 

 bryos reared at 10°, 15°, and 25° C relative to 

 development time to stage 9 at 20° C. Correction 

 factors should be approximately proportional to 



Figure l. — Symbols represent age-stage relations of mostBre- 

 voortia tyrannus embryos in experiments (unadjusted data) at 

 10° C, 15° C, 20° C, and 25° C. Solid lines are regression lines of 

 embryo age U4 ) on developmental stage (S) with experimental 

 data adjusted for preexperimental time and temperature. Re- 

 gression equation at 10° C is A = 25.476(S - 1); 15° C, A = 

 9.295(S - 1);20°C.A = 4.948(S - 1);25°C,A = 3.311(S - 1). 



development rates at different temperatures if the 

 effect of delay in attaining experimental tempera- 

 tures is small relative to incubation time to stage 

 9, and development rates are linesir, as they ap- 

 pear to be (experimental (unadjusted) data points 

 in Figure 1). When the experiments began, em- 

 bryos had reached the early blastodisc stage of 

 development; the age at that stage, therefore, for 

 each incubation temperature, was estimated by 

 multiplying the appropriate correction factor by 5 

 h. Development data were adjusted by adding to or 

 subtracting from experimental data the difference 

 between the expected age at the early blastodisc 

 stage at 10°, 15°, and 25° C from the age observed 

 at 20° C. Derivations of correction factors are pre- 

 sented in Table 5, and adjusted data on embryonic 

 development in Table 6. 



Age was regressed on embryonic stage of de- 

 velopment (S) by least-squares linear regression. 



Table 6. — Aejjusted data on the embryonic development ofBre- 

 voortia tyrannus incubated at four temperatures. 



Temper- 

 ature 



Age Embryonic Temper- 



(h) stage ature 



Age 



(H) 



20 C 



25" C 



Embryonic 

 stage 



Table 5. — Derivation of correction factors to adjust development data for differences between experi- 

 mental and preexperimental temperatures during the first 5 h of embryogenesis in Brevoortia tyran- 



945 



