taken. Also in 1970, Japanese longliners provided us 

 with gonads and detailed information of six addi- 

 tional mature striped marlin caught near the Revil- 

 lagigedo Islands Oat. 19°N, long. 111°W). 



Field sampling of specimens involved examina- 

 tion of fishes during the same day in which they were 

 caught. Each fish was weighed and measured (eye- 

 fork length). The body cavity was then opened and 

 the gonads excised. Adhering fascia were removed 

 and the gonads weighed. In 1970 the length and 

 volume of each gonad was measured. During 1969 

 and 1970 ovarian tissue was sampled with a cork 

 borer following a method used by Yuen (1955) 

 wherein two transverse borings through the ovary 

 are made at approximately Vs the distance from each 

 end. These two samples from each fish were pre- 

 served in Gilson's fluid (Simpson, 1951), which ren- 

 dered the ova much easier to measure and handle. 

 This treatment appears to have no obvious differen- 

 tial effect on the ova diameters or shape (Schaefer 

 and Orange, 1956). 



The samples were kept in Gilson's fluid from 2 to 

 18 mo during which time the ova became separated 

 from the ovarian tissue. Each sample was then 

 gently stirred and a random sample of ova was mea- 

 sured with an ocular micrometer at 30 x magnifica- 

 tion. Ova diameter measurements were taken on 

 whatever axis fell parallel to the micrometer gradua- 

 tions. Several authors (Clark, 1925, 1934; June, 

 1953; Otsu and Uchida, 1959; and Yuen, 1955) have 

 concluded that random measurements regardless of 

 the axis produced reliable results. 



Because differential maturation of ova was found 

 in bigeye tuna (Yuen, 1955) we took integrated sam- 

 ples with the cork borer. Later examination of ma- 

 ture striped marlin and sailfish ovaries, however, 

 showed no evidence of either cross-sectional or lon- 

 gitudinal variation in ova size within ovaries. We 

 tested for cross-sectional variation by taking radial 

 subsamples from a 10 mm thick transverse section 

 near the middle of one of the largest, most mature 

 striped marlin ovaries. The ova diameter frequency 

 distributions (Fig. 4) of three samples radiating from 

 the center were similar. Likewise, anterior, middle, 

 and posterior subsamples from two striped marlin 

 and one sailfish ovaries showed no evidence of lon- 

 gitudinal variation (Fig. 5). 



The 95th centile egg diameter was determined 

 from the size frequency distribution of 300 eggs 

 measured at random as described by Schaefer and 

 Orange (1956). "Maximum ova diameter" as used 

 by us was the largest size class interval (0.066 mm 



a. n 301 



b. n-301 

 c . n = 30J 



OVA DIAMETER (mm) 



Figure 4. — Ova diameter frequency polygons of subsam- 

 ples taken near the middle of a mature striped marlin 

 ovary; a — central, b — intermediate, c — peripheral. 



OVA DIAMETER Imml 



Figure 5. — Ova diameter frequency polygons from one 

 mature sailfish and two striped marlin. Samples were 

 taken from the anterior, middle, and posterior areas of the 

 left ovary. 



increments) containing ova from a sample of 50 ova 

 measured at random. 



Description of Gonads 



Detailed description of the gonads and spawning 

 products of billfishes were published by Merrett 

 (1970) and La Monte (1958). In our studies we found 

 strong evidence of gonadal assy me try (Table 1). For 

 striped marlin, the left gonad averaged larger than 



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