178 



The Philippine Journal of Science 



1917 



are kept busy distributing them to various parts of the Islands. 

 The decrease in the number of mosquitoes is very noticeable, 

 and the Governor of the Islands writes : 



The top-minnows have been a decided success. Where ponds have 

 swarmed with larvae of mosquitoes, the top-minnows have entirely cleaned 

 them out in a few days. 



Letters from other persons in the Islands have been to the 

 same effect. 



When returning to the Philippine Islands from the United 

 States in 1913 I secured two dozen mosquito fish at Honolulu, 

 placed them in a glass jar in my stateroom, and brought them 

 to Manila. The offspring of these fish now number many 

 thousands and are being widely distributed throughout the 

 Philippine Islands and the Orient, as will be seen in the follow- 

 ing report.^ 



DESCRIPTION OF THE MOSQUITO FISH 



The mosquito fish, Gamhusia affinis (Baird and Girard), is 

 very small. The female when full-grown is about 5 centimeters 

 (2 inches) in length; the male is smaller. The general color 

 is light olive, with the belly silvery. The female has a distinct 

 blackish spot on each side of the belly. There is one small fin 

 on the back (dorsal) which has seven rays, three fins on the 

 belly (ventrals and anal), and one fin on each side (pectorals). 



In this species the sex is easily 

 distinguished by the shape of 

 the anal fin; in the male this 

 fin is long and slender and the 

 anterior rays are modified to 

 form an intromittent organ. In 

 the female the anal fin is large 

 and normal in shape, with ten 

 rays. The mouth is small. The 

 eye is large. These fish usually 

 swim near the top of the water. 

 It seems to matter very little 

 whether the water is fresh or 

 brackish, clear or muddy, warm 



Fig. 1. Top minnow, or mosquito fish, Gam- qj. qq]^ They thrlve in all SOrtS 

 busia affinis Baird and Girard ; a, male ; 

 b, female. About actual size. 01 piaCeS. 



*An additional shipment of mosquito iish was ordered from Honolulu, 

 but the fish received proved to be Melinesia latipinnis, and so were not 

 liberated. 



