340 THE AQUARIUM 



means of a sheet of glass, a narrow space being kept for 

 the passage of the babies, but most experienced aquarists 

 prefer simply to stock the tank thickly with vegetation, 

 and trust to this for protection for the young fishes, rather 

 than risk the life of the mother in unnatural and cramped 

 quarters. When emitted the young are about one-quarter 

 inch in length, and able to take small Crustacea and fine arti- 

 ficial foods almost from the very first. They grow rapidly, 

 and under favorable conditions reach maturity in from two 

 to three months. The adults may be given the dry prepa- 

 rations, with an occasional meal of animal food. 



Next in popularity comes the Sword-tail Minnow 

 {Xiphophorus helleri), a fish which for beauty and hardi- 

 ness is most satisfactory. It is a native of Mexico, and 

 well-grown specimens are from two and one-half to three 

 inches in length. It is brilliantly colored, the sides being of 

 iridescent blue and green, with a red lateral stripe extend- 

 ing the entire length of the fish. The male is characterized 

 by the development of the lower portion of the tail, which 

 terminates in a sword-like projection, about one inch in 

 length and bright green in color. Helleri, as they are popu- 

 larly known among their admirers, are generally inveterate 

 persecutors of their young, and it is necessary to isolate the 

 females if it is desired to breed them. Both young 

 and adults may be treated as with the preceding, but 

 the present species is somewhat more carnivorous in 

 habit. 



The genus Gambusia contains a number of small, pug- 

 nacious fishes, known as top-minnows. G. holbrooki is an 

 excellent tank fish, and very popular among aquarists. It 

 ranges from southern Illinois through the southern states 

 into Mexico. The males of the typical form are whitish, 

 thickly blotched with black, some specimens having the 

 background entirely obscured. The female is considerably 



