MINNOWS GAMBUSIA AFFINIS AND CYPEINODON VAMEGATUS. 5 



OBSERVATIONS ON FEEDING. 



The habit of surface swimming in this species is correlated with the 

 fact that it seeks and acquires most of its food at or near the surface 

 of the water. It feeds very largely upon the larvse of insects when 

 these are available ; accordingly, it has been found to be of great value 

 as an eradicator of mosquitoes, and herein lies its greatest economic 

 importance. For this reason, also, it has been planted in many places 

 where it is not native, and the results have been gratifying. Wliile 

 aquarium feeding does not, as a rule, teach us much about a creature's 

 habits of feeding in nature, a few experiments in this connection are 

 nevertheless worthy of mention. An adult female, about 43 mm. in 

 length, had been held in a battery jar since early spring and regularly 

 fed with finely minced fish. On August 2, 1914, she wa^ fed 140 mos- 

 quito larvse between 11 a. m. and 12.15 p. m. The larvae were all 

 of large size and nearly ready to pupate, being from 6 to 8 mm. in 



^'^^^n 



Fig. 2.—0ambusia affinis. Top minnow. Female. 



length. All except four were eaten by 12.30 p. m. When observa- 

 tion was made again at 5.30 p. m. all the larvge had been consumed. 

 At 6 p. m. 25 additional larvae were supplied. Nearly all of these 

 were immediately eaten, and aU had disappeared by 9 p. m. It was 

 clear, however, that her appetite was satisfied. The abdominal walls 

 were greatly distended and it was evident that she had eaten all that 

 she could hold. 



That its Service in the destruction of mosquito larvae probably be- 

 gins on the day that the fish is bom is evidenced by the fact that 

 fish only a few hours old devoured larvae that were fed to them. 

 At this early age they were unable to swallow large larvae, but the 

 Avriter has seen them swallow larvae more than half the total length 

 of the fish itself. Considerable difficulty is apparently encountei'od 

 in swallowing a morsel of this size, and a portion of the larva is often 

 visible 1 minute after the process of swallowing is begmi. It was 

 sometimes observed that one such morsel did not satisfy the appetite 

 and that a second one was taken. 



