MATURITY AND SPAWNING OF ALBACORE 



293 



0.3 0.4 0.5 



EGG DIAMETER(MM) 



Figure 5. — Frequency curve of 550 egg diameters meas- 

 ured from a late developing ovary of a 55-pound albacore 

 taken in Hawaiian waters on June 15, 1955. The curve 

 was derived by smoothing the data twice by a moving 

 average of three. 



04 0.5 06 



EGG DIAMETER (MM ) 



Figure 6. — Frequency curve of 550 egg diameters meas- 

 ured from an advanced ovary of a 47-pound albacore 

 taken in Hawaiian waters on June 8, 1955. The curve 

 was derived by smoothing the data twice by a moving 

 average of three. 



RESULTS OF GONAD EXAMINATION 

 NORTH PACIFIC 



Since the gonads of albacore in the North Pacific 

 are generally thin and ribbonlike (early develop- 

 ing), the sexes are often difficult to distinguish by 

 gross examination in the field. For this reason, 

 gonads of both sexes were collected and the sex 

 was determined in the laboratory by microscopical 

 examination. Of the gonads of 126 fish examined, 

 62 were ovaries and 64 were testes. 



The ovaries, the bulk of which weighed less than 

 50 grams, contained only early developing eggs; 

 the maximum egg diameter measured was 0.25 

 mm. The most enlarged pair of ovaries (131 

 grams) obtained from the largest female fish 

 sampled (length 108.1 cm., weight 58 lbs.) con- 

 tained eggs which measured less than 0.13 mm. in 

 diameter. The testes were also immature. 



Although large fish (longer than 90 cm.) were 

 not well represented in the sample, field observa- 

 tions of the gonad condition of longline-caught fish 

 gave supplementary evidence that North Pacific 

 fish were either sexually immature juveniles, or 



adult fish with early developing gonads. Table 6 

 lists the observations, based strictly on gross in- 

 spection, recorded by various members of the POFI 

 staff. Presumably, the gonads of these large fish 

 were sufficiently enlarged so that sex could be de- 

 termined with some assurance. While the obser- 

 vations recorded as "spent," "spawned-out," and 

 "recovering" might be questioned, there is little 

 doubt that the "immature" fish, corresponding to 

 our early developing category, were correctly 

 designated. The observation dated January 28, 

 1955 (table 6), for a male albacore of 93.3 cm., is 

 not necessarily indicative of advanced maturity. 

 Male albacore taken in tropical and subtropical 

 waters almost invariably contain some milt in the 

 testes regardless of the size of the gonads. Brock 

 (1943) found that milt could be squeezed from the 

 testes of albacore captured off the coast of Oregon, 

 but the females from this region were judged to be 

 immature. 



Our observations indicate that albacore in the 

 central and eastern North Pacific are either 

 sexually immature fish, or are adults which do 

 not show signs of near-spawning. Partlo (1955) 



