WARNER: REPRODUCTIVE BIOLOGY OF PIMELOMETOPON PULCHRUM 



to induce earlier transformations by starving the 

 individuals. Moe (1969) has carefully worked out 

 the age distribution of sex reversal in the serranid 

 Epinephelus morio, and found a rather smooth 

 period of transition from female to male over at 

 least 5 yr (ages 5 to 10), at a rate of about 15% of 

 the individuals in a year class reversing per year. 

 In a less comprehensive survey, McErlean and 

 Smith (1964) estimated that transformation oc- 

 curred at age 10 or 11 in Mycteroperca microlepis 

 (Serranidae), and speculated that the age of the 

 fish had more effect on sex reversal than the 

 length. 



To determine the effect of individual size on sex 

 transformation in P. pulchrum, mean lengths of 

 males and females in each age class were com- 

 pared (Figure 15). If length is closely related to sex 

 reversal, one would expect males to be larger than 

 females of the same age, and this was found in 

 both the Catalina and Guadalupe populations. In 

 every age grouping where sample size permitted 

 statistical analysis, males tended to be larger than 

 females. Five of the seven groups tested (one-sid- 



350 - 



E 

 E 

 -300 



X 



I- 

 d 



z 



LlI 



Q 



< 250 



Q 



Z 



200 



150 Jr 



6UADALUPE IS. 



AGE (YEARS) 



Figure 15.-Mean lengths for successive age classes of males and 

 females of Pimelomefopon pulchrum. Sample sizes are shown for 

 each point, and standard error brackets are given when samples 

 are large enough. For clarity, standard error brackets for males 

 point to the right, and brackets for females point to the left. 



ed ^-test for difference in means) were sig- 

 nificantly different at the 5% level or less, and the 

 remaining two were significant at the 10% level. 



An assessment of the effect of age on sex 

 reversal was made in similar fashion, comparing 

 the mean ages of males and females in successive 

 size groupings (Figure 16). If sex reversal were 

 closely related to the age of an individual, then 

 males would tend to be older than females in a 

 given length group. The relationship between age 

 and sex is less strong (Figure 16). Sample sizes are 

 not large, and the range of ages encountered in a 

 sample is small relative to measured length values, 

 so fewer significant results might be expected. 

 Only one size group was found where males were 

 significantly older than the females. However, the 

 existence of several large negative t values in 

 groups where the age of females is greater than 

 that of males supports the idea that size is more 

 important than age in effecting sex change. 



The high average age of females in the larger 

 size groupings of both populations (Figure 16) was 

 not expected, and suggests that the individual 

 growth rate may also be involved in sex reversal. 

 The large separation between male and female 

 mean ages begins with the 300-mm size grouping 

 at Catalina, and the 200-mm group at Guadalupe. 

 Inspection of Figure 8 reveals that at about these 

 lengths, the proportions of males and females un- 

 dergo an abrupt shift. A large percentage of the 

 individuals in the populations apparently reverse 

 sex at these sizes. Furthermore, the difference in 

 ages between males and females of lengths above 

 these "critical" sizes appears to be significant. The 

 mean age of females larger than 300 mm at Cat- 

 alina is 7.9, a full year older than males in the same 

 size range (^31 = 1.51, P<0.10). Similarly, females 

 larger than 200 mm at Guadalupe have a mean age 

 of 9.5 yr, and males at that size range average 7.0 

 yr (^32 = 2.80, P< 0.001). Thus the females that 

 pass through the "critical" lengths without 

 changing sex appear to be those individuals with 

 relatively low rates of growth, suggesting both 

 that slow growing individuals tend to be refrac- 

 tory to sex change, and that fishes with high rates 

 of growth change sex more readily. The data of 

 Figure 15 support this idea, as males are faster 

 growing (larger) members of each age class. A 

 check of the back-calculation information revealed 

 that the growth rates of the large females were 

 consistently low throughout their lifetime, and 

 those of the small males had been high relative to 

 other members of the age class. 



277 



