52 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



Maturing (Continued) 



Stage F : Mode of the most mature group between 0.59 and 



0.69 mm. 

 Stage G : Mode of the most mature group between 0.69 and 



0.79 mm. 

 Stage H : Mode of the most mature group between 0.79 and 



0.89 mm. 

 Stage I : Mode of the most mature group between 0.89 and 



0.99 mm. 



Ripe 



Stage J : Mode of the most mature group at about 1.00 mm. ; 



some ova segregated in the lumina of the 



ovaries. 



Spawned out 



Stage K : Ovaries with a few loose ova in the lumina, in- 

 cluding some which are undergoing degenera- 

 tion. 



These stages are shown graphically in figure 3 

 which has no connotation of time, but simply 

 illustrates the developmental stages from the im- 

 mature, or resting, stage to the spawning stage. 

 With the exception of stage J, which is repre- 

 sented by the ova from only one fish, the polygons 

 are pooled frequencies of several fish of the same 

 maturity classification. The number of indi- 

 viduals included in each frequency is indicated 

 at the right. Except for stage A, the pooled 

 frequencies were reduced to the basis of 300 ova 

 (the number measured from each fish). 



Eipe ovaries from only one female yellowfin 

 tuna were present in the 1950 collections. Fur- 

 thermore, examples of the preceding two stages 

 of maturity, H and I, totaled only six among the 

 fish sampled, suggesting perhaps that, during or 

 just before spawning, yellowfin tuna bite less on 

 the longline hooks or migrate to an area or a depth 

 not being fished. Schaefer and Marr (1948) 

 offered these hypotheses to account for the absence 

 of spawning yellowfin tuna in the live-bait 

 boat catches in the waters off Costa Rica during 

 their investigations in 1947. 



It may be seen in figure 3 that as the last group 

 of ova evident in the frequency polygons pro- 

 gresses toward maturity, a second group becomes 

 differentiated and also progresses toward matu- 

 rity. The progression of the modes of these suc- 

 cessive groups is more evident in figure 4, where 

 the frequency distributions from figure 3 are ex- 

 pressed as deviations from the average frequency 

 polygon of stages B through J. The deviations 

 were smoothed twice by a moving average of 3 to 

 remove chance fluctuations. In this form, the 



maturing group at about 0.30 mm. in stage C and 

 at 0.45 mm. in stage D can be clearly distinguished 

 by appearance from the immature group. Fur- 

 thermore, the deficit of 0.20-mm. ova, beginning 

 with stage E, suggests that fewer ova develop 

 from the immature group into the intermediate 

 group after stage D than before. 



The progression of the two right-hand modes 

 is compared in figure 5 by a scatter diagram 

 wherein the position of the mode of the last group 

 (T) is plotted against the position of the mode 

 of the preceding group (X) for each of 44 fish 

 with ovaries in stages E through J. The locations 

 of the modes were determined by inspection of 

 the deviations of the individual frequencies from 

 the average frequency polygon. A coefficient of 

 correlation of 0.855 (P is considerably less than 

 0.01) emphasizes the close relation between the 

 progression of succeeding modes. 



The multiplicity of modal groups and the high 

 correlation between modes of successive ova groups 

 strongly indicate that individual fish spawn more 

 than once a year. 



Further support of the hypothesis that more 

 than one group of ova is matured by individual 

 fish during the spawning period arises from the 

 presence of semitransparent, mature ova lying 

 loosely in the lumina of the ovaries at the same 

 time that a second group of ova is developing 

 toward maturity. Among these remnants, some 

 of the ova were grayish in color with the shell 

 membranes partially collapsed ; in a few, the oil 

 globules were still discernible ; and in others, only 

 the transparent shell membranes or fragments of 

 the shells remained. That these remnants are not 

 carried over from the previous year's spawning 

 is evidenced by the fact that ovaries in the resting, 

 or immature, stage (stage A) and those in the 

 intermediate stages of maturity (stages B and C) 

 which were collected at the beginning of the year 

 showed no signs of ova remnants in the lumina 

 from recent spawnings. Furthermore, the condi- 

 tion of the mature ova remaining in the ovaries, 

 as previously described, indicates that the group 

 of which they were a part probably had been ex- 

 truded only a short time before. Finally, among 

 fish with ovaries in the maturing stages, eight 

 samples in stages E, F, and G were found in which 

 the ovaries were very much enlarged and turgid 

 and in which remnants of mature ova were scat- 



