Zoological Studies

Sex Ratios and Sexual Maturity of Swordfish (Xiphias gladius L.) in the Waters of Taiwan

Sheng-Ping Wang, Chi-Lu Sun* and Su-Zan Yeh (2003) Lower jaw fork length (LJFL) was measured in 551 female and 386 male swordfish at Tungkang, Nanfangao, and Shinkang fish markets during September 1997 to July 2000, and ovaries were removed from 208 of the swordfish collected at the Shinkang fish market during July 1998 to June 2000 whose LJFLs ranged between 95 and 257 cm. The sex ratio (the proportion of females to the total number of females and males) increased as the LJFL increased beyond 150 cm (sex ratio = 1 x 10^-4 LJFL^1.6601), and all fish with LJFLs of greater than 210 cm were females. The estimated mean body length at sexual maturity (L₅₀) for females was 168.2 cm; the smallest mature female was 135 cm. Among mature females, 79% were in the developmental stage of ripening and 21% were in the resting stage; no individual was in the spawning or recently spawned stage. No hydrated oocytes were observed in any of the female gonad samples. These observations indicate that swordfish do not spawn in the waters of Taiwan. According to the relationship between developmental stage and the diameters of oocytes, 50% of individuals will be reproductively active at an oocyte diameter of 372.1 µ which can be used as an index for reproductive activity of swordfish in the waters of Taiwan.