SEX RATIO IN GAMBUSIA. 395 



greater abundance of males which begin to appear in September 

 are the result of young fish that are becoming sexually mature, 

 for among these fish the males are quite as numerous as the fe- 

 males. After the following May or June nearly all of the fish, 

 born the previous year, have become sexually mature and the 

 young of the current season are still nearly all immature fish. 

 Then the very rapid decline in the male population, already men- 

 tioned, takes place. 



Further study has convinced the writer that the main reproduc- 

 tive season of Gambusia is much more limited than stated by him 

 (1917 and 1921). In catching and transporting large numbers of 

 fish while engaged in the study of Gambusia in its relation to 

 mosquito control, it became evident that, although some gravid 

 females are seen in early spring and during the fall, 1 the main re- 

 productive season lasts only about three months, namely June, 

 July and August. A very sudden decrease in the number of 

 gravid females was noticed at Augusta, Ga. (where special atten- 

 tion was given to this matter for several years in succession) 

 during the early days of September and in that locality, at least, 

 the reproductive season may be said to end by Labor Day. The 

 end of the spawning period evidently is not greatly influenced by 

 temperature, as has been the contention of various writers, for the 

 month of September at Augusta generally is one of the warmest 

 of the summer. Furthermore, the writer has for two winters 

 (1925-26 and 1926-217) kept two lots of adult Gambusia, con- 

 taining a fair percentage of males, in the terrapin nursery house 

 at the U. S. Fisheries Biological Station, Beaufort, N. C, which 

 is kept at summer heat. Yet reproduction was not induced dur- 

 ing the winter months. It was noticed, however, that gravid fe- 

 males appeared somewhat earlier in the spring in the lots in the 

 terrapin house than among fish that wintered out of doors. The 

 influence of temperature on reproduction in Gainbiisia, therefore, 

 does not appear to be very pronounced. 



The scarcity of gravid females in " midsummer " was noticed 

 by Barney and Anson (1921). These authors thought this to be 

 due to the scarcity of males, stating that such a " condition would 



1 In the extreme southern parts of the United States, as at Key West, 

 some gravid females are present at all seasons of the year. 



