KENDALL and NAPLIN: DIEL-DEPTH DISTRIBUTION OF ICHTHYOPLANKTON 



was significant, indicating that during the three 

 time periods examined, the larvae moved to shal- 

 lower depths at night. 



Snake Eel 



Snake eel eggs ranked sixth in abundance, with 

 an overall mean of 19 eggs/100 m^. Fewer eggs 

 were taken in the deeper tows, though slightly 

 more eggs occurred at 4 m than at the surface 

 (Figure 5). No significant difference between day 

 and night egg catches was apparent (Table 4). 

 However, at all depths except 15 m, more eggs 

 usually were taken at night. At 15 m, more 

 eggs were caught in the daytime. Significantly 

 more eggs were caught on each succeeding day of 

 the cruise. 



The numbers of eggs in various stages taken 

 during the cruise are shown in Table 11. Because 

 the eggs were not stratified with depth, and 

 because relatively few eggs were taken at each 

 depth, we combined the eggs from the four depths 

 sampled during the first experiment. The eggs are 

 divided into seven batches that were spawned on 

 the 3 d of sampling and the preceding 4 d. Where 

 some arnbiguity as to the boundary between older 

 batches exists, replicate samples were staged to 

 provide better definition of individual batches. At 

 each sampling time, four groups of developmental 

 stages were present. Spawning began at 2100 h 

 each day, and was restricted to a relatively short 

 period of time. Most eggs had h^.tched by 2100 h 

 4 d after being spawned. These data for develop- 

 ment times have been used in a description of 

 embryonic stages in this species (Naplin and 

 Obenchain 1980). 



The numbers of eggs in each batch are plotted 

 according to developmental stage and time of day 

 in Figure 11, from which the duration of each stage 

 can be readily determined. For example, complete 

 epiboly required about 12 h and took place from 

 0900 until 2100 h the day after the eggs were 

 spawned. Table 12 is the corresponding complete 

 developmental timetable for the snake eel. The 

 regular fluctuations in egg number apparent in 

 Figure 11 are even more clearly displayed in 

 Figure 12, which depicts the total number of snake 

 eel eggs over time. The fluctuations occurred on a 

 12-h cycle, and are possibly the result of tidal 

 periodicity in spawning. As sampling progressed, 

 the vessel gradually drifted into an area of more 

 concentrated spawning, which was somewhat 

 west of and closer to the 30-fathom (54.9 m) line 



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