MINNOWS GAMBUSIA AFFINIS AND CYPRINOIX)N VAKIEGATT-S. H 



in the spring of the same year even succeeded in producing two small 

 broods before the arrival of cool weather. 



A female that produced 6 broods during one season, averaging 40 

 young to a brood, would have 240 descendants of the first generation 

 by the end of the season, assuming that all survived. Now, if the 

 sexes in the first brood occurred in the apparently normal proportion 

 of 5 males and 35 females, and if each female produced three young 

 in September, the total number of young of the second generation 

 resulting from this brood would be 105. It appears that by the end 

 of the season the original female would have given rise to a family of 

 240 offspring of the first generation and 105 offspring of the second 

 generation. There are few, if any, fishes whose output of eggs does 

 not outnumber the young of Gamhusia, but the chances of survival 

 for young delivered alive as compared with eggs and young hatched 

 from them, are probably 1,000 to 1. It seems reasonable to conclude, 

 therefore, that under natural and normal conditions no native fish 

 multiplies more rapidly than Gamhusia affinis. 



SUMMARY. 



1. Gamhusia. affinis usually inhabits shallow, stagnant waters, 

 whether fresh or brackish, and it thrives under conditions of rela- 

 tively high temperature if the proper amount of food is available. 



2. It is a very hardy fish, adapting itself readily to many different 

 natural conditions as well as to life in the aquarium. 



3. Its food consists largely of the larvae of insects, but it feeds also 

 upon a variety of other animal and plant substances. It sometimes 

 eats its own kind, even its own offspring, especially in the restricted 

 environment of an aquarium. 



4. One medium-sized female may destroy as many as 165 large 

 mosquito larvae in a single day. 



5. In the region of Beaufort the fish produces its first brood of 

 young for the season during the month of May and continues to breed 

 throughout the summer until as late as October. It may produce 

 during a single season six or more broods, averaging 40 young to a 

 brood. 



6. Females separated from males in the spring shortly before the 

 first brood is born continue to produce young throughout the season. 

 If separated from the male even during late fall no young will result 

 the following spring, but infertile eggs wiU be deposited. 



7. Young are delivered during the day, one, two, or three at a 

 time. Some come head first, some tail first, and others in a coiled 

 position. The period of labor may comprise an hour or the greater 

 portion of a day or even portions of two days. 



8. The modified anal fin of the male, which is the external character 

 that distinguishes the sexes, may be fully developed when the fish 



