SIZE AT FIRST SPAWNING 
If fish sizes are plotted against stages of maturity, the size at first spawning should 
become evident. Although fish larger than the size at first spawning could be in any stage of 
maturity, those below this size would all be immature. A plot of this type was made (fig. 5) 
using fish weight and relative ovary weight 
as measures of size and maturity respectively. 
140 — 1 1 
L . a In this plot the maturing fish (those 
feo =| & CENTRAL EQUATORIAL ° _| having relative ovary weights of 4 or greater) 
5 © WESTERN EQUATORIAL 5 A _| were almost all over 20 kg. (44 lbs.) while 
= fale oa : a e | four of the five immature fish (those having 
oO OF 3 S 0 relative ovary weights of 3 or less) weighed 
= |p : gage | o “aot ne ‘| less, The number of fish below 20 kg., is 
se EOE Sen Shire oe We ‘| insufficient to set more definitely the size 
= | Gini ie 2 tot. 8 <° | at first spawning. 
= 60} ~ APS O80 HY G0 S| 
a r Oo Ruden $ x 2065 Towstens oS Data from the equatorial Pacific and 
ik 4oh 8 6) OPBs g: 52 eee o-| the Hawaiian area are contradictory as to 
L he i ae OF cs RONG -+_ what happens in the ovaries after spawning. 
20 ¢- 6 : 8 ion ines | Figure 5 indicates that once a fish spawns its 
B g ovaries never revert to the immature stage 
0 eeeeennen (Rae hail of having only primitive eggs. This is shown 
! 5 10 20 30 40 50 by the fact that, with one exception, none of 
RELATIVE OVARY WEIGHT X 103 the relative ovary weights of fish greater than 
20 kg. were less than 4. Many fish weighing 
as much as 100 kg. (220 lbs.) from Hawaiian 
waters were immature according to their 
relative ovary weights. 
Figure 5, --Plot of fish weight against relative 
ovary weight. 
Since there were relatively few fish of 20 kg. and under, the ovaries of these fish were 
subjected to further study in an effort to find indications of past spawning, such as residual eggs. 
Although the absence of these eggs would not necessarily mean that spawning had not taken place, 
as they might have been completely reabsorbed, their presence would mean that spawning had 
occurred, Five of the seven ovaries examined did not have residual eggs. Only two fish of 14 
and 17 kg. (31 and 37 lbs.) did have residual eggs, The size at first spawning, therefore, ranges 
from 14 kilograms (possibly less) to 20 kilograms, This agrees with Kikawa (1953), who stated 
that the size at first spawning is roughly 90 to 100 cm. This corresponds to fish of 16 to 21 kg. 
(see table B, footnote 3), 
Moore (1951), working on the age and growth of the yellowfin in the Hawaiian fishery, 
estimated that the yellowfin grows from a weight of 7 to a weight of 46 pounds (3 to 20 kg.) inits 
second year of growth. If the bigeye, which weighs slightly more than yellowfin of comparable 
lengths and attains a greater size, can be assumed to have a growth rate of this magnitude in its 
early years, the range of size variation within a year class could include individuals of 14 and 
20 kg. Only a greater sampling of fish in the lower size range and a study of age and growth, 
however, will definitely answer the question of age of sexual maturity. 
TEMPORAL AND SPATIAL DISTRIBUTION OF RIPE OVARIES 
Positions of capture of bigeye in the late maturing and mature stages (fig. 6) show that 
these fish are widely scattered in the equatorial regions, Kikawa (1953) who worked in the 
western equatorial Pacific also found this to be true but with an apparent concentration in the 
Keats Bank area (5°53,8'N., 173°29.4'E.). 
Although ovaries in the late maturing and mature stages were obtained 400 miles to the 
AG ° 
southeast of Hawaii at 14 N., 150°W. , they were completely absent among the 503 of the Hawaiian 
collection. 
16 
