FISHERY BULLETIN: VOL. 79, NO. 4 



Table 8. — Stages of Gulf Stream flounder eggs taken on day 1 during the vertical distribu- 

 tion study of ichthyoplankton in the Middle Atlantic Bight, July 1974. Roman numerals refer 

 to batch numbers that were assigned to the eggs. 



Total 



312 



355 



251 



307 



291 



251 



305 



158 



full days to hatch; hatching occurred primarily in 

 near-surface water beginning around 0900 h the 

 morning of the fourth day after spawning. 



Staging the eggs also revealed that they were 

 stratified with depth, with early stages being 

 taken in the deeper nets (Figure 10). Precell stages 

 were taken primarily at 30 m, while eggs with 

 several cell divisions and early blastula and 

 blastodermal cap stages were taken mainly at 15 

 m. From 0900 to 1200 h the morning after spawn- 

 ing, early germ ring stages gradually shifted from 

 4 m to the surface. After 1200 h, the later stages 

 were found at all depths sampled, but were con- 

 centrated at the surface and 4 m. 



By using Stokes' law for calculating the rising 

 velocity of the eggs, which have an average 

 diameter of 0.70 mm, we estimated when the eggs 

 were spawned and how old they were when sam- 

 pled. If eggs were spawned on the bottom (57 m), 

 they required 7 h to rise to 30 m and another 5.8 h 

 to reach 15 m. As several precell and cell stage 

 eggs appeared from 1500 to 1800 h in the 30 m net, 

 the eggs were probably spawned between 0800 

 and 1100 h. Table 9 is a timetable for development 

 of Gulf Stream flounder eggs based on the stages 

 of eggs in Table 8 and on egg rising velocities 

 calculated from Stokes' law. 



The overlap between batches of the Gulf Stream 

 flounder eggs as compared with the clearly de- 

 fined batches of Atlantic whiting eggs may be 

 related to two factors. First, the incubation time 



of Gulf Stream flounder is about twice that of 

 Atlantic whiting eggs; therefore, eggs from twice 

 as many batches are present in the plankton 

 at once. Second, because Gulf Stream flounder 

 spawns on the bottom, the eggs were subjected to 

 turbulence and mixing by the time they were 



Table 9. — Timetable of development of Gulf Stream flounder 

 eggs based on collections made during the vertical distribution 

 study of ichthyoplankton in the Middle Atlantic Bight, July 1974. 



718 



