NOTES ON THE HABITS. MORPHOLOGY OF THE REPRODUCTIVE 

 ORGANS, AND EMBRYOLOGY OF THE VIVIPAROUS FISH 

 GAMBUSIA AFFINIS. 



By ALBERT KUNTZ, PH. D., 

 St. Louis University School of Medicine. 



INTRODUCTION. 



Gambusia affinis (Baird and Girard), according to Smith (1907), "is found along the 

 coast from Delaware to Mexico and reaches inland as far as Illinois. In North Caro- 

 lina it is excessively abundant in the lowlands, in swamps, ditches, creeks, and also 

 in the open waters of the rivers." "■ It is known primarily as a fresh-water species, 

 but occurs also in brackish water. Early in July and again on August i, 191 2, a con- 

 siderable number of these fish were taken along the swampy borders of Mullet Pond, 

 Shackleford Banks. The specific gravity of the water in which they were taken on 

 August I was 1. 008 1. This reading, however, does not represent the normal specific 

 gravity of the water along these swampy borders, as considerable rain had fallen during 

 the preceding 12 hours. At the time the above reading was taken, water from the 

 central part of Mullet Pond showed a specific gravity of 1.0106. On July 24, 1912, a 

 single specimen was caught in the seine in the terrapin pens at the Beaufort Laboratory. 

 This was a large female, bearing mature, unfertilized eggs. The water in these pens 

 is salt, only a very little fresh water entering through small pipes from an artesian well. 



Twenty-four of the fish taken in Mullet Pond on August i were transferred to sea 

 water in a small aquarium, where they remained for a period of 10 days. At the end 

 of this time i was found dead. The remaining 23 were apparently in a normal con- 

 dition; they had, however, lost much of their pigment and their tissues had become 

 slightly transparent. 



During the entire month of July, 1912, these fish were present in abundance in a 

 brooklet emptying into Beaufort Harbor just east of Beaufort. The water in this 

 brooklet is supplied largely by springs. It was reddish brown with organic matter 

 and contained considerable debris. Most of the fish used in this study were taken in 

 this brooklet. 



The generic name Gambusia is derived from the name "Gambusina, " commonly 

 used in Cuba, which means "small" or "of no importance." While of no commercial 

 value, this species has an important economic worth. It feeds largely on insects and 

 insect larvae. Wherever it inhabits waters in which mosquitoes breed the mosquito 

 larvae constitute its principal food. The introduction of these fish into the natural 



o Smith, H. M.: Fishes of North Carolina. North Carolina Geological and Economic Survey, vol. ii, p. 153. 



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