Hermaphroditic Skipjack 1 
Richard N. Uchida 2 
Two PAIRS of skipjack ( Katsuwonus pelamis ) 
gonads, each having male and female compo- 
nents, have come to my attention in the past 
3 years. The first was received from Mr. Thomas 
S. Higa, proprietor of a Honolulu fish retail 
market, in April 1937. Mr. Higa recovered the 
gonads from a neighboring fish retailer who 
had discovered them in a freshly eviscerated 
16-lb. skipjack. This fish was captured by the 
"Orion,” a commercial skipjack vessel, on April 
11, 1957, off Makua, Oahu, from a school of 
15- to 18-lb. skipjack. 
The ovo-testes ( Fig. 1 ) were typically paired 
and elongate, joined posteriorly, and weighed 
121 gm. (fresh weight). The male and female 
components were easily discernible. The left 
gonad was divided into three segments; the an- 
terior one-sixth and posterior one-third were 
ovarian and the remainder testicular. The right 
gonad was divided into two segments; about 
two-thirds of the anterior portion was testicular 
and the remainder ovarian. Figure 2 shows the 
length of each of these segments. 
The cream-colored testicular sections were 
solid and somewhat flattened in cross-section, 
and did not seem to be atypical in any way. 
There was no running milt present, but their 
size suggested that they were in a rather ad- 
vanced stage of maturity. All ovarian sections 
were pinkish, but differed in firmness. The pos- 
terior segments were hollow and flabby, with a 
ribbed internal cavity extending their entire 
length. The single anterior ovarian section was 
nearly round in cross-section and rather turgid. 
Detailed examination of the ovo-testes was 
made after they had been preserved in 10 per 
cent formalin. The longitudinal duct of each 
1 Published with permission of the Director, U. S. 
Bureau of Commercial Fisheries. Manuscript received 
July 29, I960. 
2 Fishery Research Biologist, Honolulu Biological 
Laboratory, U. S. Bureau of Commercial Fisheries, 
Honolulu, Hawaii. 
testicular section could be followed posteriorly 
to the juncture of the testicular and ovarian 
segments, after which the ductus deferens be- 
came obscured in the network of blood vessels 
on the surface of the ovarian section. No open- 
ings of the ductus deferens were detected any- 
where in the area of the urogenital sinus. 
The two posterior ovarian sections were 
joined posteriorly by a single oviduct which 
opened into the urogenital orifice. No duct 
could be found in the single anterior ovarian 
segment. - 
Microscopic examination of the ova was made 
to determine their degree of maturity. The lu- 
men of the anterior ovarian section was filled 
Fig. 1. The ovo-testes of a hermaphroditic skipjack 
(ventral view). 
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