Table 1.— Ovulatory status of skipjack tuna at different times 

 following capture during June and July 1980. 



Time 



No. Unovulated Ovulating Ripe Spent 



Refrigerated 



immediately after 



capture 16 16 



Captive females, 



0-5 h after 



capture' 9 9 



Captive females, 



5-6 h after 



capture 13 1 



Captive females, 



7-8.5 h after 



capture 12 3 



Captive females, 



1 5-65 h after 



capture 20 



12 







19 



'Refrigerated after dying in transit to the laboratory; individual times of 

 death not known, but <5 h after capture in all cases. 



could be completed within 8 h after capture and 

 occurred even in females that were so seriously 

 traumatized that they died within a few hours 

 after this time. Unless manually stripped, the 

 ripe females released ova into the holding tank, 

 and by the next day, 15 to 24 h after capture, 

 were in a spent condition. Spawning behavior 

 was not observed to occur. Instead, their behavior 

 was invariably abnormal, as is typical for skip- 

 jack tuna during their first days in captivity, 

 with individuals swimming aimlessly about the 

 holding tanks. 



The ovulated ova, both those released spontan- 

 eously into the tanks and those stripped from 



Table 2.— Mean sizes (mm) 1 of ova in largest and second largest modal group 

 of developing ova in skipjack tuna killed and refrigerated immediately after 

 capture, or refrigerated after dying in transit to the laboratory. 



Date 



31 July 



Refrigerated on capture 



Died in transit 



No 



15July 4 



21 July 7 



22 July 3 



Largest 

 group 



0.62 

 0.62 



Second 

 group 



No 



Time 

 (h) 2 



Largest 

 group 



0.41 

 043 



'Standard deviations 0.02-0.04 

 2 Time between capture and death 



<45 



<5 



Second 

 group 



ter (Table 2). Of those kept alive, all but 1 of the 

 13 specimens examined 5 to 6 h after capture 

 were ovulating but not yet ripe, while 8 of 12 

 examined after 7 to 8.5 h were ripe. Such ripe in- 

 dividuals yielded about 100,000 to over 150,000 

 ova when stripped. All but 1 of the 20 specimens 

 examined 15 to 65 h after capture were spent. On 

 all five occasions when the holding tanks were 

 monitored for the presence of spawned ova, large 

 numbers of ova were evident by the morning fol- 

 lowing delivery. 



These observations clearly demonstrated that 

 female skipjack tuna caught and kept alive dur- 

 ing this time of year rapidly underwent the final 

 stages of ovarian maturation and then ovulated 

 ripe ova into the ovarian lumen. This response 



ripe females, were normal in size and appear- 

 ance. They were spherical, transparent, aver- 

 aged about 1.0 mm in diameter, and had a single 

 oil globule about 0.24 mm in diameter. The fertil- 

 ization rate of ova stripped from females about 8 

 h following their capture was only about 40% to 

 50%; this may reflect the quality of the ova or the 

 small amounts of viscous milt squeezed from the 

 dissected testes. The embryos hatched in about 

 30 to 31 h at 25° to 26°C and started feeding on 

 the third day after hatching. Although they fed 

 actively on rotifers, Brachionus sp., and copepod 

 nauplii, we were not able to rear any beyond the 

 12th day. 



Numerous investigators have described the 

 multimodal size distribution of developing ova in 



394 



