NOTES ON THE DIFFERENTIAL VIABILITY IN 
GAMBUSIA" 
S. W. GEISER 
Barney and Anson (1921) in writing of the fluctuating sex- 
ratio in the common top-minnow, Gambusia aMnis B. & G., have 
expressed (p. 61) conclusions with respect to a differential death- 
rate for the sexes quite at variance with data of my own. Briefly 
stated, they conclude that in the shipping of Gambusia for stock- 
ing ponds in mosquito-control work, the female has a higher 
death-rate than the males and they explain this upon the assump- 
tion that the male is more resistant to high temperatures than the 
female. 
During the past year, I obtained from the Director of the U. S. 
Bureau of Fisheries Laboratory at Beaufort, North Carolina, 
two lots of these fish, totalling 1489 individuals. They were sent 
to Baltimore in fairly equal installments, and at different seasons 
of the year. On each occasion they were a little more than forty- 
eight hours in transit. One shipment (693 fish) was sent in cold 
table I 
November 12, 1920 | March 22, 1921 
Maees 
Females 
Uncert. 
Total, Males 
Females 
Total 
Number of fish 
shipped 
176 
452 
65 
693 
91 
705 
796 
Percentage of 
population 
25.3 
65.2 
9.4 
99.9 
11.4 
88.5 
99.9 
Sex-ratio 
100.0 
256.8 
100.0 
774.7 
Died in transit . . . 
80 
136 
36 
252 
79 
249 
328 
Percentage of 
dead population . . 
31.7 
68.3* 
100 
24.08 
75.9 
99.98 
Death-rate per 
thousand 
454.5 
300.8 
553.8 
363.6 
868.1 
353.2 
412.0 
Mortality index- 
number for males 
male death-rate 
female death-rate 
1.556 
2.458 
1 Grateful acknowledgements are due to Professor S. O. Mast for help and encour- 
agement in studies on a part of which the present paper is based. 
* Includes the “uncertains,” i. e., young so small that their sex' is not readily ascer- 
tained. Note: The death-rate of males in March, as compared with their death-rate in 
November is as 1.910 to 1. The death-rate for females compared in the same way is 
1.174 to 1. In March, too, most of the females are heavily gravid. 
