CKUSTACEA AS FOOD FOR YOUNG FISH. 



PTIYLLOPODA OR FAIRY SHRIMPS. 



The Phyllopoda, or fairy shrimps, have not been definitely indi- 

 cated as possible food for fishes, althoiio;h they occur in every part of 

 the world, being found from sea level up to more than 10,000 feet. 

 The distribution of all species, however, is apt to be local and their 

 occurrence irregular and uncertain. A certain pool may swarm with 

 them, while they may be entirely absent from near-by pools. A par- 

 ticular species may be abundant one season and scarce or entirely 

 absent for several years, or it may appear regularly season after sea- 

 son. The greater part of the North American species occur in the 

 Great Plains. Several species of Eubranchippus, however, abound in 

 the Central and Eastern States. Most phyllopods occur, often in 

 great numbers, in small fresh-water pools such as are formed by 

 spring rains. Pearse (1918a) relates an instance of nearly half a 

 bushel of dead 

 Apus bodies hav- 

 ing been observed 

 by him on the bot- 

 tom of a shallow 

 dried-up depres- 

 sion about 20 feet 

 in diameter. 



The majority 

 of phyllopods are 

 very small, al- 

 though one spe- 

 cies of Apus attains a length of 70 mm. (something over 2.75 inches), 

 but another species, a common fairy shrimp {Eubranchippus vernalis) 

 grows to about 38 mm. (about 1.5 inches). The smallest species are 

 inclosed in shells, in appearance suggesting tiny bivalve mollusks, 

 and range in size from about 3 mm. (0.117 inch) to 16 mm. (about 

 0.669 inch) in length. 



All phyllopods are of separate sexes and males are usually much less 

 common than females. The eggs of most genera can resist prolonged 

 desiccation ; in fact it is apparently necessary for the development of 

 some species that the eggs should first be dried and afterwards im- 

 mersed in water. The mud of dried-up pools often contains large 

 numbers of eggs which may be conveyed long distances by winds, 

 birds, or other means. Many foreign species have been reared from 

 dried mud brought home by travelers. Many eggs float when placed 

 in water and development takes place at the surface. 



Fig. 1. 



-Fairy shrimp. Branchinccla paludosa, male and female. 

 Enlarged three times. After Ward and Whipple. 



CLADOCERA OR WATER FLEAS. 



The most common of the branchiopods are the so-called water fleas 

 belonging to the order Cladocera. These entomostracans have a wide 

 distribution and some species are cosmopolitan. The majority of 

 species found in this country are also found in Europe. They may 

 occur in various sorts of environment. Some species are purely lim- 

 netic, some intermediate, some littoral, and others indifferent, that 

 is, they may occur in any one of the environments. The cladocerans 

 are plankton organisms abundant throughout the summer. 



