382 American Fisheries Society 



require considerable modification when applied to young fish 

 within the limits of this study. 



The food of the young gizzard shad may be roughly 

 grouped into the following kinds, in order of their importance 

 as noted in the examination of stomach and intestinal contents : 

 microscopic unicellular plants (algae), microscopic animals, and 

 filamentous algse. Mud usually forms from ten to thirty per 

 cent of the contents, and a similar quantity is unrecognizable 

 plant debris. Mud is often entirely lacking from the stomach 

 contents and it is my belief that it is merely incidental to the 

 manner of feeding. No consideration is given, therefore, to its 

 varying amount in the digestive tract. 



The gizzard shad feeds by swimming through the water 

 with its mouth open in an apparently aimless manner. The 

 presence of such masses of microscopic material in the diges- 

 tive tract is accounted for in part when the feeding apparatus 

 of the fish is examined. The very numerous fine gill rakers 

 on the gill arches oppose the escape through the gill slits of very 

 small objects which enter the mouth of the fish with the water 

 of respiration. Thus like a very fine sieve, these allow the 

 water to pass out through the gill slits as the fish swims along, 

 while the minute organisms are retained and introduced into 

 its alimentary canal. 



The gizzard shad is the most wonderful combination of 

 tow net and centrifuge that one could desire. Wherever this 

 fish was found, it was not necessary to do any towing to get 

 an estimate of the number and kinds of microscopic plants, for 

 the stomach contents represented a concentrated sample of the 

 plankton. The number of different kinds of microscopic algae 

 found in an identifiable condition in the digestive tract of the 

 gizzard shad is markedly large. In a single fish taken at Buck- 

 eye Lake on July 1, fifty species and varieties of algae were 

 found ; from the specimens examined to date from the various 

 localities named above, the number of species exceeds 140 and 

 will doubtless reach considerably higher. The majority of 

 these are unicellular and colonial forms included in the group 



