Feb., 1921] 



Algal Food of the Gizzard Shad 



115 



as being concentrated in one gizzard shad, he will get some idea 

 of the vast number of individuals present at one time in the 

 fish. In fact, the gizzard shad is about the most wonderful 

 tow net that one could desire to get an estimate of the kinds and 

 proportionate numbers of microscopic algae present in a body 

 of water. In a single fish taken at Buckeye Lake on July 1, 

 fifty species and varieties of algae were found; from all the 

 specimens examined to date, one hundred and forty different 

 forms are recorded. 



The presence of such masses of microscopic material in the 

 digestive tract of the gizzard shad 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. Thus, like a very 

 fine sieve, these allow the water to pass out through the gill slits 

 as the fish swims along with its mouth open, while the minute 

 organisms are retained and pass into its alimentary canal. 



Animal vs. Pla^it Food. 



When a comparison of the number of animal and plant forms 

 is made (See Table I below), it is noted that plants make up 

 from seventy to one hundred per cent of the food material of the 

 gizzard shad; animal forms, from zero to thirty per cent, depend- 

 ing upon the particular fish and locality. It should be further 

 noted that even the animal organisms, fed upon by the gizzard 

 shad, depend directly for their food supply on the microscopic 

 algae. The animal forms .include copepods, cladocerans, rotifers, 

 and protozoa. 



TABLE I. 



Maximum and minimum percentages of plant and animal food in gizzard shad, 

 based on examination of fish collected June 15 — September 15. 



The majority of the algal forms belong in the order Proto- 

 coccales. For convenience of comparison each individual identi- 

 fied is placed in one of seven groups: Myxophycece, Peridinece, 

 EuglenidcE, Bacillarice, Desmidiacece, Protococcales, and the 

 filamentous algas. 



