Biology of Wahoo — IVERSEN AND YOSHIDA 
373 
influence both species similarly and are of 
greater importance than inter-specific com- 
petition for food, though both appear to feed 
on similar animals. 
REPRODUCTION 
In samples from the Line Islands, at all 
times of the year the percentage of males 
tends to be higher in the northern islands 
than in the southern islands (Fig. 2). This 
consistent trend or gradient suggests a migra- 
tion of wahoo to maintain itself, unless there 
is varying differential mortality between sexes 
among areas, which seems unlikely. Such a 
gradient might be related to spawning move- 
ments but we are unable to describe them. 
The wahoo in the Line Islands appear to 
spawn over an extended period of time, as is 
common with fish found in tropical waters. 
Fig. 2. Percentage of male wahoo by trolling areas, 
March 1955 to February 1956. (The number in each 
sample is shown in parentheses). 
Cursory field examination of 80 females in 
March and of 143 in November and Decem- 
ber, using categories devised by Marr (1948: 
201),— i.e., immature, ripening, ripe, spawn- 
ing, and spawned out — revealed all stages 
of maturity during both periods. 
In order to estimate the number of eggs 
per spawning the size frequency distribution 
of ova in an apparently ripe ovary was deter- 
mined for a fish of 131 cm. fork length (Fig. 
3). Only eggs larger than 8 micrometer divi- 
sions, or 0.184 mm., were measured. An 
abundance of undeveloped or primitive eggs 
was present in the ovary, but most of these 
were not measured. The group 0.184-0.46 
Fig. 3. Frequency distribution of egg diameters from 
a single female, 131 cm. fork length, captured May 
1955 at Fanning Island. 
mm. contained the larger of these "stockpile” 
eggs; the group from about 0.46 mm. to 0.94 
mm., with a prominent mode at 0.62 mm. 
appeared to be maturing eggs. This latter 
group of eggs may be likened to the "type 
B” or developing eggs described by Tester 
and Takata (1953: 42) from the aholehole, 
Kuhlia sandvicensis. This one specimen showed 
no clear evidence of more than one mode 
among the developing eggs. The maturing 
group of eggs (> 0.46 mm.) in the ovaries 
of this female wahoo was estimated to num- 
ber about 6.1 million. This estimate was ob- 
tained by weighing the formalin-preserved 
