Table 24. — Monthly record of occurrence of various items in stomach contents of gizzard shad in 1952-55 



'Indicates the more plentiful items. 



phytoplankton; still others maintain that they 

 subsist mostly on zooplankton. All agree, how- 

 ever, that they are "filter-feeders," and this 

 feature alone, I believe, best describes their 

 feeding habits. They filter the water of whatever 

 particulate matter it contains. Shad captured in 

 open waters contained mostly free-floating phyto- 

 plankton; those captured among the attached 

 plants, such as Cladophora, Myriophyllum, and 

 Ceratophyllum, ingested Cladocera, Copepoda, 

 Rotifera, and small aquatic insect larvae; those 

 captured in very turbid waters were filled largely 

 with mud. That they do, however, add to their 

 diet from the bottom debris is evidenced by the 

 presence in the gizzard of sand particles of di- 

 ameters in excess of 0.25 mm. This size of sand 

 is not held in suspension even when the water 

 is highly turbid. Although the bottom is available 

 to the shad at all times, I have not found sand 

 in shad gizzards from December through March. 

 Food particles could not be identified during 

 this period. The taking of sand when food is 

 plentiful suggests its use as an aid in grinding 

 by the gizzard — or it may have been taken 

 accidentally along with food. 



The appearance of the food differs in the three 

 distinct regions of the alimentary apparatus — 

 the pharyngeal pockets, the gizzard, and the 

 intestine (especially the forepart which bears 

 caeca and which is often swollen with ingested 

 material). When reference is made to food in 

 the gizzard shad without regard to a definite 

 region of the digestive tract, I use the term 

 "stomach contents." 



The pharyngeal pockets, suggested by Lagler 

 and Kraatz (1944) to be accessory to the digestive 



system, have, to my knowledge, not been thor- 

 oughly examined in studies of food of gizzard 

 shad. The pouches frequently are empty, but 

 when food is plentiful and the fish's gut is full 

 of food (especially zooplankton), the pharyngeal 

 pockets contain as much food as the gizzard. 

 The contents of these pockets appear straw- 

 colored and consist mostly of Cladocera and 

 Copepoda along with strands of filamentous 

 algae. Here are found the larger items of the 

 shad's diet, and they are, as yet, not broken apart. 

 The zooplankters still have their full complement 

 of appendages and the filamentous algae are in 

 strands. 



The gizzard is frequently empty, and only 

 rarely is it turgid with food. The composition of 

 food in the gizzard is similar to that of the 

 pharyngeal pockets. The zooplankters, however, 

 are more or less dismembered, and the strands 

 of filamentous algae are short. The gizzard 

 contains, in addition, many unicellular algae, 

 rotifers, and some sand along with plant and 

 animal debris. 



The intestine usually contains food, although 

 the amount is scanty in winter. Material from 

 the intestine is fragmented and mostly unrecog- 

 nizable — it has the appearance of bottom debris 

 or mud, especially on gross inspection. 



I have found no compact matter exceeding a 

 diameter of 3 mm. in the stomach contents of 

 gizzard shad, except Tendipedidae and small 

 Leptodora during certain seasons. Nor have I 

 found in them bits of attached aquatic plants, 

 except after severe storms when small fragments 

 were presumably torn loose and were recovered 

 by the filtering apparatus. 



GIZZARD SHAD IN WESTERN LAKE ERIE 



421 



