Biology of Wahoo — Iversen and Yoshida 
stout-bodied fish, such as some of the tuna, 
have a considerably smaller exponent. Ex- 
amples are: yellowfin from Costa Rica, which 
have an exponent of 2.940 (Schaefer 1948: 
119); and bigeye tuna, Parathunnus sibi (Tem- 
minck and Schlegel), sampled in Hawaii, 
which have an exponent of 2.9304 (Iversen 
1955: 2). 
PARASITES 
Although no diligent search was made for 
parasites, the list given in Table 3 indicates 
that the wahoo is rather heavily parasitized. 
In the course of the examination of food 
items, trematodes about one inch in length 
when partially contracted were regularly noted 
at the posterior end of the stomach. Nigrelli 
and Stunkard (1947: 188) have carefully ex- 
amined the genus Hirudinella and, on the basis 
of 33 specimens taken from wahoo captured 
in both the Atlantic and Pacific oceans, regard 
all forms of this giant trematode in the wahoo 
as belonging to a single species, H. ventricosa 
(Pallas). 
377 
In the 220 stomachs examined during 
March and November-December 1955 the 
number of giant trematodes per stomach 
ranged from 0-17 (Table 4). In all except the 
largest fish, two trematodes per fish were 
most commonly encountered, suggesting 
that this number represents a physiological 
equilibrium between host and parasite. On 
the other hand in the largest length group 
(160-179-9 cm.), four trematodes per stomach 
were commonly found. 
SUMMARY 
1. The availability of wahoo caught by troll- 
ing and longline fishing indicated the 
existence in the Line Islands of a small 
population that was most abundant in 
shallow water within a few miles of land. 
2. Males were relatively more abundant in 
catches from the more northerly islands 
than in those from the more southerly 
islands. 
3. Examination of wahoo gonads showed all 
TABLE 3 
Parasites of wahoo from the Line Islands, 1955 
NUMBERS PRESENT 
PER WAHOO 
RATE OF INFESTATION 
PARASITE 
SITE OF INFECTION 
Per cent 
Number 
of wahoo 
examined 
Trematoda 
Neothoracocotyle acanthocybii 
(Meserve) 1 
Between gill filaments 
Numerous 
(high) 
Didymocystis acanthocybii 
Yamaguti 1 
Head inside gill 
covers 
Numerous cysts — 
2 worms/cyst 
51.0 
104 
Hirudinella ventricosa (Pallas) . . . 
Caudal end of the 
stomach 
0-17 
98.2 
220 
Nematoda 
Mass of worms em- 
bedded in belly wall 
Many 
(slight) 
Copepoda 
Brachiella sp 
Within joint of 
pectoral fins 
2 in each joint 
98.3 
118 
Gloiopotes sp 
Outside surface of 
body and caudal fins 
Many — variable 
54.2 
96 
Pennella sp 
Embedded in belly 
wall with hind por- 
tion protruding 
1 or 2 
9.8 
92 
^Trematodes kindly identified by Dr. H. W. Manter, University of Nebraska, Lincoln. 
