208 



Fishery Bulletin 88(1). 1990 



Q FEMALE/SUBSURFACE 



MALE/SUBSURFACE 



O FEMALE/SURFACE 



□ MALE/SURFACE 



\R 



n 



0-54 55-59 60-64 6569 70-74 75-79 80-84 85-89 90-94 95-99 -10 

 FORK LENGTH {cm) 



Figure 1 



Length-frequency distributions for male and female South Pacific 

 albacore tuna examined in this study. Surface troll-caught fish and 

 subsurface longline-caught fish are differentiated. 



are suspended by the mesentery which contains a fat 

 body closely associated with the gonad between it and 

 the dorsal body wall (Godsil and Byers 1944). The fat 

 body will be discussed in a later section. Testes are thin 

 and ribbon-like in immature fish, and develop into 

 somewhat flattened, whitish-yellow organs which are 

 relatively solid as the fish advance in maturity. Ova- 

 ries in immature fish closely resemble immature testes 

 in appearance. They become progressively enlarged in 

 length and girth and tend to be somewhat pinkish in 

 color as the fish progresses in maturity. 



We initially made casual observations, when collect- 

 ing gonad tissue samples for genetic-variability studies 



of North Pacific albacore, that the right gonads were 

 most often larger than those on the left side. The pres- 

 ent study of nearly 200 South Pacific albacore showed 

 that while right and left gonads of both sexes were 

 about the same length, the cross-sectional area and 

 volume of the right ovaries and testes were regularly 

 larger than those on the left side. Figure 2 shows a pair 

 of ovaries and associated fat bodies, portion of the 

 digestive tract, and ventral fin dissected from a 94-cm 

 FL North Pacific albacore. The disparity in size be- 

 tween the right and left ovaries and associated fatty 

 bodies is typical of what we have observed in this study 

 and in casual observations. 



Size differences between right and left testes 



Measurements of the cross-sectional area (mm-) of the 

 medial sections of the right and left testes provide 

 quantitative estimates of size differences between the 

 two. Data summarized in Table 2 show that the right 

 testis was larger than the left in 72% of male fish ex- 

 amined, the two testes were equal in size in 2%, and 

 the left was larger than the right in 23%. 



The results given in Figure 3 show that the dissimi- 

 larity in size increases with increasing fork length. The 

 right testis is about 28-82% larger than the left in fish 

 less than 80 cm FL, but increases to about 6(5-75% 

 larger in fish over 80 cm. Data on displacement vol- 

 umes measured on a sample of the right and left testes 

 showed results similar to those made on the measure- 

 ments of cross section. Examination of relationships 

 between fork length and cross-sectional area of the 



