Schaefer Spawning time, frequency, and batch fecundity of Thunnus albacares 



107 



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m 



^ 



% 



<3Wt 



V 



m 



*~ s 



n 



88 



B 



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Figure 7 



Vas deferens relatively devoid of sperm from three yellowfin tuna, Thunnus albacares (A and B; C and D; 

 E and F), sampled during 0001-1200 h. The rectangles in left panels indicate the regions shown under 

 higher magnifications in right panels. Bar = 1 mm in A, C, and E; 0.1 mm in B, D, and F. e = epithelium; m 

 = myoid tissue; s = sperm. 



These data indicate that evidence of recent spawn- 

 ing in males is detectable for only about 12 hours 

 after the spawning event. Apparently the lobules, 

 which are full of sperm in mature fish, refill the main 

 sperm duct during this time, and the other charac- 

 teristics, such as the convoluted shape of the duct 

 and the conspicuous dark staining of the vas defer- 

 ens epithelium return to the state observed in 

 prespawning individuals. Assuming that spawning 

 males are detectable between 0001 and 1200 h, an 



estimate of the daily spawning frequency of males 

 during the six days of sampling in 1986 and the four 

 days in 1987 at Clipperton Atoll can be derived. Ten 

 of the 12 fish in 1986 and 17 of the 21 fish in 1987 

 that were sampled between 0001 and 1200 h were 

 classified as having spawned in the past 12 hours. 

 Thus about 83.3% and 81.0% of the males had 

 spawned within the past 24 hours in 1986 and 1987, 

 respectively. This indicates that the mean interval 

 between spawnings was about 1.20 days in 1986 and 



