NOTES Ratty et al: Reproducwe biology of Thunnus .^lalunga 



213 



70 71-80 81-90 >90 



FORK LENGTH (cm) 



Figure 9 



Comparison of sexual maturity levels of male South Pacific albacore 

 by fork length. 



vations differ from those reported for many other tele- 

 osts, where the main duct is located along the dorsal 

 surface of the testis and may not be present in imma- 

 ture stages of the testis (Grier et al. 1980). 



As the production of sperm increases, morphological 

 changes occur in the main sperm duct. In the immature 

 testis the main sperm duct is thin-walled and highly 

 convoluted (Fig. 8A). In the mature testis the main 

 duct, when filled with sperm, has much thicker wails 

 and is less convoluted and more rounded (Fig. 8B). The 

 production of sperm is also associated with increased 

 vascularization of the testis, first in the caudal portion 

 followed by the medial and rostral portions. 



Ratios of observations characterizing immature and 

 mature stages of sperm-duct development (thin:thick. 



convoluted;round, large:small) showed a higher propor- 

 tion of mature sperm ducts in the left testis than the 

 right. The results also reveal that sperm-duct develop- 

 ment is greatest in the caudal, intermediate in the 

 medial, and least in the rostral portions of both the 

 right and left testes. As expected, there was an increas- 

 ing trend in sperm-duct development with increasing 

 fork length. 



Sexual maturity 



Fish were classified into five levels of sexual maturity 

 based on relative abundance of sperm observed in the 

 testes: (1) No sperm present in any portion of either 

 testis; (2) immature, few sperm observed in one or more 

 portions of either or both testes; (3) intermediate, few 

 or some sperm in more than one portion of both testes, 

 but not the sperm duct; (4) mature, many sperm ob- 

 served in most portions of both testes and the sperm 

 duct; and (5) fully mature, many sperm observed in all 

 portions of both testes and the sperm duct. 



Information on sexual maturity in relation to fork- 

 length size categories is given in Figure 9 and Table 

 4. Slightly more than 50% of fish 50-70 cm FL were 

 immature, including 28% (derived from Figure 9) with 

 no sperm present in any portion of either testis. Over 

 40% were in the intermediate level and 7% were judged 

 sexually mature, but none was fully mature. Fish in size 

 groups larger than 70 cm FL had a lower proportion 

 of immature individuals than did fish less than 70 cm, 

 ranging from 18% to 40% (Table 4), including only 

 3-10% with no sperm present in any portion of either 

 testis (derived from Figure 9). The proportion of fish 

 in the intermediate level of maturity ranged between 

 20% and 46% for fish in size groups larger than 70 cm 

 FL. The percentages of fish in the mature and fully 

 matui'e categories were nearly the same for size groups 

 71-80 cm and 81-90 cm FL, 36% and 40%, respective- 

 ly, but only 21% for the size group over 90 cm. The 

 71-80 cm FL size group had the highest proportion of 

 fully sexually mature individuals, 23%, while only about 

 5% of fish larger than 90 cm were fully sexually mature 

 (derived from Figure 9). 



The lower proportion of mature and fully mature in- 

 dividuals in the size group larger than 90 cm FL ap- 

 pears to be related to geograpliic region and/or type 

 of fishing gear. Figure 10 compares maturity levels be- 

 tween fish caught in the midocean region of the cen- 

 tral South Pacific by surface trolling and those caught 

 in coastal waters off New Zealand by subsurface 

 longline. It is evident in Figiu'e 10 that a higher pro- 

 portion of immature and a lower proportion of mature 

 and fully mature individuals were caught in coastal 

 waters than in the midocean region, even though the 

 longline-caught fish were much larger, averaging 92.3 



