IMMATURE 



SPAWNING OF YELLOWFIN TUNA 

 INTERMEDIATE MATURING 



51 



RIPE 



I 



CD 



2 



Z 



OVA OIAMETER IN MILLIMETERS 



Fiottbe 2. — Frequency curve of 1,000 ova diameters measured from a ripe ovary of a 121-lb. yellowfin tuna taken in 



Hawaiian waters, June 11, 1950. Only ova measuring more than 0.13 mm. in diameter were included. The line 



a+2b+c 

 represents the original data (dots) smoothed by the formula 



was made of 1,000 ova more than 0.13 mm. in 

 diameter taken from a ripe ovary (fig. 2). The 

 group with diameters measuring from 0.76 to 1.23 

 mm. includes ova almost ready for spawning, and 

 it can be easily distinguished from the intermediate 

 and maturing groups below 0.65 mm. in diameter. 

 The immature group is indicated in figure 2 by a 

 dotted line. 



Spawned out: Toward the end of the spawning 

 season the ovaries decrease in size, become hollow 

 and flaccid, and gradually resume the appearance 

 of those in the immature stage. Following spawn- 

 ing, ripe ova remnants in various stages of degener- 

 ation are found in the lumina of the ovaries. Ova 

 in the intermediate and maturing groups which 

 remain in the follicles at the conclusion of spawn- 

 ing take on a deep greenish or brownish color in 

 formalin, and the yolk granules appear as dark 

 specks, indicating that these ova are degenerating 

 and undergoing absorption. During the spawn- 

 ing season ripe ova remnants often are present in 

 the lumen of the ovary at the same time that the 



ovary is still very much enlarged and apparently 

 maturing a group or successive groups of ova. 



Since the previously noted developmental 

 groups marking maturation of the ova were 

 clearly evident, and since these groups showed 

 iutergradation in fish collected at different times 

 through the year, the ova-diameter frequency 

 polygons of each sample in the collection were 

 classified according to the position of the mode of 

 the most mature group of ova present. The fol- 

 lowing 11 arbitrary stages were defined: 



Immature 



Stage A : Mode at about 0.08 mm., no ova above 0.18 mm. 



Intermediate 



Stage B : Mode of the most mature group below 0.29 mm. ; 



no ova above 0.34 mm. 

 Stage C : Mode of the most mature group between 0.29 and 



0.39 mm. 

 Maturing 

 Stage D : Mode of the most mature group between 0.39 and 



0.49 mm. 

 Stage E : Mode of the most mature group between 0.49 and 



0.59 mm. 



