NOTES 



THE SEX RATIO AND GONAD INDICES OF 

 SWORDFISH, XIPHIAS GLADIUS, 



CAUGHT OFF THE COAST OF 

 SOUTHERN CALIFORNIA IN 1978 



In the tropical and subtropical Pacific, swordfish, 

 Xiphias gladius, about to spawn are found through- 

 out the year but are most abundant from March to 

 July (Palko et al. 1981). There is, however, little in- 

 formation on the reproductive potential of swordfish 

 during their summer and autumn migrations into 

 the Southern California Bight, a temperate region 

 encompasing the principal U.S. west coast swordfish 

 fishing grounds. In 1978 scientists from the South- 

 west Fisheries Center collected the gonads of sword- 

 fish harpooned in the Bight (from Point Conception 

 to the United States-Mexico border) in order to 

 determine sex ratios, gonad indices, and the repro- 

 ductive condition of these fish. 



Methods 



Ninety swordfish were sampled from 25 August 

 through 20 November 1978. After capture their 

 gonads were preserved in 10% Formalin 1 and, in the 

 laboratory, were weighed to the nearest gram and 

 their sex determined visually. Ovarian sections used 

 in the histological analysis were obtained from seg- 

 ments removed from the centers of the ovaries. Seg- 

 ments were imbedded in Paraplast and 8 ^m sections 

 were cut, stained in iron hematoxylin, and counter- 

 stained in eosin. 



Two gonad indices were calculated for each pair 

 of ovaries to permit comparisons with two existing 

 studies on the sexual maturity of Pacific swordfish. 

 The first (from Uchiyama and Shomura 1974) is 

 simply the percentage of the fresh weight of the 

 ovaries to the total weight of the fish: 



GI = (W/L 3 ) x 10 4 



(2) 



r,r WT-0 ^ nn 



GI = - x 100 



WT-F 



(1) 



where GI = gonad index, 



WT-0 = fresh weight of both ovaries, and 

 WT-F = fresh weight of whole fish. 



The second index (from Kume and Joseph 1969) is 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



FISHERY BULLETIN: VOL. 84, NO. 1, 1986. 



where GI = gonad index, 



W = fresh weight of both ovaries in grams, 



and 

 L = post-orbital fork length in centime- 

 ters. 



Because the gonads used in this study were pre- 

 served, and thus subject to shrinkage and loss of 

 weight, it was necessary to estimate their fresh 

 weight using the relationship (from Uchiyama and 

 Shomura 1974): 



Y = e 



In X-0.155 

 0.969 



(3) 



where Y = estimated fresh weight of ovaries, and 

 X = weight of preserved ovaries. 



The estimated weight loss due to preservation was 

 as high as 7%. 



Results and Discussion 



All 90 swordfish collected were mature with fork 

 lengths ranging from 133 to 218 cm. Of these, 23 

 (26%) were males and 67 (74%) were females for a 

 sex ratio of 0.34:1 (M:F). Although the proportion 

 of females varied among months, our sample sizes 

 were too small to demonstrate such variation. 



Female swordfish in our sample all had gonad in- 

 dices that were considerably lower than those of com- 

 parable studies. Uchiyama and Shomura (1974) col- 

 lected 16 pairs of ovaries from swordfish caught near 

 Hawaii and found three pairs to be ripe These had 

 gonad indices (from Equation (1)) of 6.4, 8.4, and 9.8 

 whereas our highest value (from Equations (1) and 

 (3)) was 1.0. Kume and Joseph (1969) examined 362 

 pairs of ovaries from swordfish captured in the east- 

 ern Pacific (east of long. 130°W) and found two ripe 

 specimens whose gonad indices (from Equation (2)) 

 were 10.8 and 11.1. By comparison, the highest from 

 our study (from Equations (2) and (3)) was 1.8. These 

 results indicate swordfish in the Southern Califor- 

 nia Bight during our sampling period were not 

 spawning. 



A histological analysis was performed on a subset 

 of 16 pairs of ovaries from our sample Histological 

 analyses can be used to determine not only if a fish 



185 



