60 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



during the season. On the whole, however, if 

 Marr's definitions were grouped, placing his "im- 

 mature" and "spawned-out" in "nonspawning" 

 ("spawned-out" ovaries would have to be exam- 

 ined with a hand lens to eliminate those which 

 still contained the yellowish, maturing ova in the 

 follicles), and his "ripening" and "ripe" in 

 "spawning," relatively few fish would be placed 

 in different categories than those resulting from 

 weighing the ovaries and the fish and plotting 

 their coordinates on figure 6. 



NUMBER OF OVA SPAWNED 



To estimate the number of ova produced at a 

 single spawning by yellowfin tuna of different 

 sizes, calculations were made for 11 fish over the 

 size range 47.2 to 88.0 kg. (104 to 194 lbs.) . (See 

 table 6.) While estimations for a greater number 

 of specimens would have been desirable, the labor 

 involved in separating the ova from the follicles 

 and the subsequent ova measurements precluded 

 the study of additional material. 



Table 6. — Estimated number of ova produced at one 

 spawning by yellowfin tuna 



Weight of fish 



47 kg 

 63 kg 



66 kg 



67 kg 

 69 kg 

 69 kg 

 61kg 

 62 ke 

 69 kg 

 80 kg 

 88 kg. 



Calculated 



number of 



maturing 



ova 



Thousands 

 2,370 

 3,390 

 4,340 

 6,170 

 3,230 

 6,510 

 3,580 

 5,610 

 6,380 

 6,000 

 8,590 



Ovaries were selected in which the most mature 

 group of ova could be easily distinguished from 

 ova being developed for subsequent spawnings 

 and yet they were not sufficiently mature that any 

 ova had been lost by spawning. Since it has been 

 suggested that individual fish probably spawn 

 more than once during a single breeding season, 

 it is possible that subsequent spawnings would con- 

 tain fewer ova ; therefore, to make all estimations 

 comparable, only ovaries in stage F which showed 

 no evidence of previous spawning during the sea- 

 son were used. Accordingly, the estimates repre- 

 sent the number in the first of several possible 

 spawnings. The method employed in calculating 

 the number of ova was as follows : Ovaries from 



an individual fish were removed from the formalin 

 preservative, and when sufficiently drained, they 

 were weighed on a beam balance to the nearest 

 0.1 gram. A small sample of approximately 0.5 

 gram was removed from the ovaries and weighed 

 on an analytical balance to the nearest 0.001 gram. 

 The ova in the sample were teased out of the 

 follicles, and measurements and counts were made 

 of all ova composing the most mature group. The 

 total number of ova in this group was calculated 

 for each fish specimen by multiplying the ratio 

 of the number of ova to the weight of the sample 

 by the total weight of the preserved ovaries. Since 

 the multiplier was in the order of 10,000, the esti- 

 mate was recorded only to the nearest ten thou- 

 sand ova. 



The data shown in table 6 indicate that the 

 number of ova produced at a single spawning 

 increases with the size of the fish. This phe- 

 nomenon has been demonstrated for many fishes, 

 including the Volga-Caspian herrings, Caspiolosa 

 caspia, C. c. saposhnikovi, C. c. volgensis, and C. c. 

 Jcesselri (Kisselevitch 1923), the grunion, Leures- 

 thes tenius (Clark 1925), the California barra- 

 cuda, Sphyraena argentea, (Walford 1932), the 

 California sardine, Sardinops caerulea, (Clark 

 1934), and the surf smelt, Hypomesus pretiosus, 

 (Schaefer 1936). The relation between number 

 of ova and size of fish for the yellowfin tuna is 

 shown graphically in figure 7. Assuming the 



60 70 80 



FISH WEIGHT IN KILOGRAMS 



Figure 7. — Scatter diagram showing relation between the 

 calculated number of ova produced for one spawning 

 and the body weight of the fish. 



