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



105 



V *^<s°Sj&.J'js£ 



0- V 





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fe n 0s 





L 





Figure 5 



Migratory-nucleus-stage oocyte and a postovulatory 

 follicle in advanced stage of degeneration in yellow- 

 fin tuna, Thunnus albacares. Bar = 0.5 mm; n = 

 nucleus; o = oil droplet; po = postovulatory follicle. 



Classification of testes and spawning 

 incidence 



The yellowfin tuna testis is bilobed and each lobe 

 consists of interstitial and germinal compartments. 

 The germinal compartments are situated within lob- 

 ules that radiate perpendicularly from the central 

 longitudinal sperm duct (vas deferens) or efferent 

 duct and terminate at the periphery of the lobe, the 

 tunica albuginea. Primary spermatogonia are distrib- 

 uted along the lobule lengths, and this typical lobu- 

 lar-type testis is classified as an unrestricted sper- 



matogonia! testis type (Grier, 1981, 1993). The lob- 

 ules of reproductively active yellowfin tuna are filled 

 with sperm that are released after completion of sper- 

 miogenesis into the lobular lumen, which is continu- 

 ous with the vas deferens (Nagahama, 1983). The 

 vasa deferentia are straight tubes with thick, mus- 

 cular walls, which merge caudally and exit through 

 the genital orifice. The lumen of the vas deferens is 

 lined along its length with cuboidal to columnar epi- 

 thelium and varies in general appearance from 

 smooth to convoluted. 



Structural characteristics of the vas deferens, sub- 

 jected to discriminant analyses, indicated significant 

 differences (F 05l3 57 =19.96, P<0.001 ) among yellow- 

 fin tuna sampled between 0001 and 1200 h (group 1) 

 and those sampled between 1201 and 2400 h (group 

 2) for the pooled 1986 and 1987 data (Table 3). The 

 results are similar for the years examined separately. 

 Although the second group, on the basis of spawning 

 time of 2230 to 0330 h, may contain males that had 

 spawned within 12 h, there were no males sampled 

 during that time interval in 1986 and only four in 

 1987. The characteristics that best distinguish be- 

 tween fish of the two groups are the amount of sperm 

 in the duct, shape of the duct, and staining charac- 

 teristics of the vas deferens epithelium (Table 3). The 

 fish from group 2 are characterized by a relatively 

 sperm-filled vas deferens, an open duct that is smooth 

 along its border, and no conspicuous dark staining 

 of the vas deferens epithelium (Fig. 6). The spaces 

 apparent in Figure 6 (C-F) between the wall of the 

 duct and the sperm clumped in the center of the duct 

 are most likely artifacts of the preparation method 

 caused by embedding the tissue sample in paraffin 



Table 3 



Summary of stepwise discriminant analyses between yellowfin tuna, Thunnus albacares 

 2400 h) for the pooled 1986 and 1987 data, using the six sperm duct characteristics. 



groups 1 (0001-1200 h) and 2 ( 1201- 



Total 



:■:;; 

 28 

 61 



81 S 



82.1 

 82.0 



27 



5 



32 



6 

 23 



29 



