Figure 15. — Enlarged view of the small intestine of the 

 gizzard shad showing three of the longitudinal folds with 

 their transverse lamellae. 



Kraatz (1924) for the gut of Campostoma ano- 

 malum in which somewhat similar folds assume a 

 zigzag arrangement. 



Transverse lamellae were present in a 22.5-mm. 

 shad. Here they were attached circumferentially 

 to the gut only — the longitudinal folds had not 

 yet formed. 



Longitudinal sections of the gut, because they 

 cut across the lamellae, appear to be villous. This 

 fact may account for the statement of Forbes and 

 Richardson that the gut possesses villi. 



Digestive Enzymes 



Only a qualitative study was made of the diges- 

 tive enzymes. Attempts to determine their quan- 

 tity or potency did not yield dependably accurate 

 results. The areas tested were: Pharyngeal 

 pockets, esophagus, gizzard, duodenum (that 

 forepart of the gut bearing the caeca), hepato- 



pancreas, gall bladder, and the first, second, and 

 third portions of the intestine. The materials 

 were prepared in the usual manner and the extrac- 

 tion made with 50 percent glycerol. 



Tests were made for the following enzymes: 

 Pepsin, trypsin, amylase, lipase, maltase, sucrase, 

 and rennin. In addition, I sought enzymes that 

 would act on chitin and cellulose. 



The enzyme giving the strongest reaction was 

 amylase (table 23). It was present in all areas 

 tested. The reactions for pepsin and trypsin 

 were moderate, whereas the reaction for lipase was 

 weak. I am at a loss to explain the significance of 

 the positive test for rennin. 



The presence of enzymes in the esophagus is not 

 restricted to the gizzard shad. Sarbahi (1951) 

 found amylase, maltase, and invertase in the 

 esophagus of the goldfish, and Kenyon (1925) 

 cited Kingsley as reporting gastric glands in the 

 esophagus of the sturgeon. 



FOOD AND FEEDING HABITS 



The young gizzard shad begins to feed about 4 

 or 5 days after hatching. The earliest food is 

 probably Protozoa and unicellular algae. When 

 the shad has attained a length of about 20 mm., 

 it feeds on the smaller of the zooplankters and 

 takes practically no phytoplankton. By the 

 time it is 30 mm. long it has assumed the adult 

 shape, and its gizzard is fairly well developed. 

 The fish now begins to feed more and more on 

 phytoplankton. 



Three opinions have been offered in the literature 

 regarding the nature of the food of adult gizzard 

 shad. Some believe they eat predominately mud ; 

 others insist that they feed almost wholly on 



Table 23. — Digestive enzymes found in the gizzard shad 

 (I( no value is given, a test was not made. The numerical ratings are: 0, negative; 1, not definite; 2, perceptible; 3, small; 4, considerable; 5, strong] 



420 



U.S. FISH AND WILDLIFE SERVICE 



