188 



Shelby D. Gerking 



Numbers of embryos in the fourth brood were so variable that 

 no relationship with length of the female could be demon- 

 strated. 



The influence of age on fecundity was proved by both field 

 and laboratory observations. Females of similar size col- 

 lected at an earlier date in the summer contained a greater 



Table I 



The effect of age on fecundity of female mosquitofish 



{Gambusia affinis) of the same size. Modified from 



Krumholz (1948) 



number of embryos than those collected later (Table I). The 

 decrease in embryo production was greatest during late 

 summer, near the end of life. Among fish born at approxi- 

 mately the same time there was a decrease in fecundity with 

 age despite an increase in size. One group of females averaged 

 49 mm. in length and yielded a mean of 205-4 embryos on 

 June 9, 1939; on July 13 the females were 52-6 mm. long and 

 gave 155 • 7 embryos; and a few remaining fish of the same age 



