10 U. S. BUREAU OF FISHERIES. 



vary greatly in the nature of their habitats, but while the three just 

 mentioned differ somewhat in this respect, they are very similar in 

 their habits. They are quick and active in their movements, their 

 thoracic legs being adapted for climbing, and their abdominal ap- 

 pendages for swimming and jumping. They dart about among green 

 water weeds, usually keeping well in shelter and swim rapidly when 

 disturbed. 



They are hardy and their habits enable them to maintain their 

 numbers, although they are not as prolific as many other crustaceans. 

 They cany their young in a pectoral brood pouch until well de- 

 veloped, and their agility and ability to conceal themselves serve to 



a considerable degree as pro- 

 tection against predacious ene- 

 mies. Among the enemies of 

 amphipods are fishes, birds, in- 

 sects, Hydra, and the plant 

 Utricularia. (Embody, 1911, 

 states that amphipods are ap- 

 parently able to escape by eating 

 their way out of the " bladders " 

 of Utricularia. 



Fig. 6. — Amphipod ; ♦' scud •' ; Caledonia The food of the f OUr SpecieS 



shrimp. Gammarus limnwus. Enlarged rliopnccprl in fViic ^-.m-ipr tq pqgpit 



twice. After Ward and Whipple. Qiscussea lu inis papei IS essen- 



tially the same for each species, 

 consisting of living and dead animals and plants; but dead animal 

 matter must not be much decomposed. Dead leaves and plant stalks 

 are readily stripped of their softer tissues, and this material probably 

 constitutes the larger portion of their natural food. 



The North American species of most importance as food for fishes 

 in fish-cutural establishments are. Gammarus fasciafus, Gammarus 

 limnwus, Hyalella knicherhockeri, and Eucrangonyx gracilis. There 

 are, however, several species of amphipods besides the above which 

 may be of considerable local importance and which would afford just 

 as good, if not better, results in the particular localities as Miy of the 

 above. The important amphipod of Europe which has received fish- 

 cultural attention is Gammarus fulex. 



Gamviarus fasciatus. — ^This scud has a rather wide distribution, 

 locally governed more or less by the character of the water. The 

 U. S. National Museum records (1907) it from the Hudson River and 

 Niagara Falls, N. Y. ; Ann Arbor, Mich. ; Lakes Superior, Delavan, 

 and Geneva, Wis.; Havana, 111.; Burlington, Iowa; Redfoot Lake, 

 Tenn. ; Brookside, W. Va. ; Washington, D. C. ; and St. Johns River, 

 Fla. 



In the vicinity of Ithaca, N. Y., Embody's observations (1911) in- 

 dicated that it was restricted to Cayuga Lake and its open tributaries, 

 but he stated that it seemed to occur most abundantly where vegeta- 

 tion was thickest and to be associated with thick masses of Massilea, 

 Elodea, Potamogeton, Myriophyllum, and Utricularia. Warm w\ater 

 seemed to be no bar to its distribution, since it was found breeding in 

 cove water where the temperature rose as high as 30° C. (86° F.). 



The larfjest Cayuga specimen measured 15.3 mm. (0.60 inch). The 

 average size of 16 egg-producing females was 8.73 plus mm. (0.34 

 inch), and the smallest of these, which was 39 days old and pro- 



