SUMMARY 
ES ee eee 
This study is based on examinations 
ere es oar of the ovaries and the eggs within the ovaries 
a) of the bigeye tuna, Parathunnus sibi. Mate- 
() rial collected from the western equatorial 
=I Sir al and central Pacific Ocean was used, 
= . 
ae oI ° ° a Investigations were made of egg 
a a ° diameter distributions in the ovaries to 
us Si . e ° 4 determine sampling procedures and the 
fre following findings resulted: (1) Ina pair 
m Ble =| of ovaries the distribution of egg diameters 
2 in the right member is the same as the 
2 | | distribution in the left member; (2) eggs 
of the most mature group in an ovary are 
5 evenly distributed throughout the ovary; 
OMesO 40 50 60 70 80 90 100 =—«110 and (3) the variance of diameters of mature 
FISH WEIGHT (KG.) eggs is least at the periphery and the pos- 
terior of the ovary. 
Figure 10.--Relation of number of eggs spawned 
to fish size, Frequency distributions of egg dia- 
meters of maturing and mature ovaries were 
multimodal. The most evident modes were 
those of the undeveloped and the most mature groups of eggs, There were suggestions of as 
many as two modes of maturing groups between these. The ovary weight relative to the fish 
weight was found to be associated with the mode of the most mature group of eggs in the ovary. 
The equation best describing the relation was calculated: Y =,0.6935 X - 0.1367 where Y is the 
modal diameter in millimeters and X is the ovary weight x 10 /fish weight. 
Indications of bigeye spawning were found in the western equatorial Pacific, the central 
equatorial Pacific, and locations 400 miles southeast of Hawaii, but none were found in Hawaiian 
waters. 
The extent of the spawning season could not be determined with certainty. Bigeye in 
advanced stages of ripeness were caught in the central equatorial Pacific in January, February, 
July, August, September, and October. In the western equatorial Pacific fish near spawning 
were taken from April through October, Evidence of more than one spawning per season was 
found. 
The size at which the bigeye first spawns was found to be about 14 to 20 kg. 
The number of eggs extruded per spawning ranges from 2.9 to 6.3 million and depends 
roughly on the size of the fish, 
20 
