214 



Fishery Bulletin 88(1). 1990 



cm FL, than troll-caught fish, averaging 69.2 cm. 

 Figure 1 shows that virtually all of the fish in the size 

 category greater than 90 cm were caught in coastal 

 waters by subsurface longline. 



Fat body 



A lobulated mass of fat-like tissue was usually observed 

 in the mesentery attached to testes and ovaries. In 

 some cases it was extremely large and well developed, 

 but quite rudimentary in others. It was generally white- 

 to-creamy in color and always formed in segmental 

 lobes. The extent of the fat body was usually coinci- 

 dent with that of the gonad, but sometimes it extended 

 a variable distance anteriorly beyond the gonad. The 

 mass of the fat body was generally correlated with size 

 of the gonad. We observed that the right testis or ovary 

 of the albacore, which is generally larger than the left, 

 usually had a larger fat body (see Figure 2). In addi- 

 tion, we observed that the fat body was proportionately 

 larger in immature fish that were meiotically inactive 

 than in fish with gonads actively producing sperm. 



Discussion 



50 



30 



PERCENT OF FISH 



10 10 



30 



50 



I I I I 



COASTAL, LONGLINE 



n = 27 



MEAN F.L. - 92.3 



1 1 1 1 



MID-OCEAN. TROLLING 



n =65 



MEAN F.L. : 69.2 



y/y M A I U H t / 



Z^- FULLY MATURE 



r 



Figure 10 



Comparison of sexual maturity levels of male albacore caught in 

 coastal South Pacific waters by subsurface longline (left) with tho.se 

 caught in midocean South Pacific region by surface trolling (right). 



According to literature pertaining to the general struc- 

 ture and function of teleost gonads, the development 

 of gonads is usually similar on both sides of the fish. 

 However, asymmetry in gonad size has been observed 

 sometimes in some species, usually at or near the time 

 of breeding (Turner 1919, Robertson 1957, Sanwal and 

 Khana 1972, Dalela et al. 1977). 



Asymmetry in gonad size appears to be common for 

 albacore, at least in prespawning stages. We observed 

 asymmetry in 95% of fish examined, with the right 

 gonad larger than the left in 72% of the cases. The 

 disparity in size increased with increasing fork length. 

 The right testis averaged about 30% larger than the 

 left in fish less than 80 cm and averaged more than 70% 

 larger in fish greater than 80 cm. We do not have data 

 collected during active spawning to ascertain if this 

 relationship exists at that stage. 



Otsu and Uchida (1959) reported that the right ovary 

 was usually slightly larger than the left in albacore 

 specimens from the central North Pacific, but they did 

 not quantify the difference. Ueyanagi (1955) noted that 

 the right and left ovaries from a mature female alba- 

 core caught in the Indian Ocean differed in weight by 

 100 grams. However, he did not indicate weights or 

 relative size of the ovaries. Partlo (1955) conducted 

 histological studies on 44 albacore from the eastern 

 North Pacific, but did not publish data on gonad size 

 or mention asymmetry. The gonads of other tunas are 

 more or less symmetrical in size and usually have no 



conspicuous fat body (Kurt Schaefer, Inter-Am. Trop. 

 Tuna Comm., P.O. Box 271, La Jolla, CA 92038, pers. 

 comm., 1 May 1989). 



The finding that meiotic activity is higher in the 

 smaller of a pair of testes is puzzling, and we have no 

 ready explanation for it. It may be that this relation- 

 ship holds true only for prespawning individuals and 

 possibly during other periods when albacore are not 

 spawning. We are unable to determine whether this 

 condition continues through the spawning cycle be- 

 cause our samples were collected over an insufficient 

 period and not in the primary geographic region where 

 South Pacific albacore are believed to spawn (Otsu and 

 Hansen 1961). A remote possibility is that the smaller 

 testis is kept in an advanced reproductive state for 

 "opportunistic" spawning and that the larger testis 

 matures only when the fish is in the more prevalent 

 location of spawning. If this is so, the species could 

 presumably extend its reproductive potential with 

 relatively low expenditures of energy. It is also possi- 

 ble that sperm are not shed by precocious fish, but are 

 reabsorbed. Progressive reabsorption of sperm by 

 Sertoli cells has been observed in rainbow trout (van 

 den Hurk et al. 1978). 



Our results show that some males less than 70 cm 

 may be sexually mature and that the proportion of sex- 

 ually mature individuals increases with increasing fork 

 length, up to 90 cm. There is a decrease in the percent- 



