46 FISHES OP ILLINOIS 



spot behind opercie in the young; fins more or less dusky. Head deep 

 posteriorly and tapering forward, 3.7 to 4.3 in length; width of head 1.9 to 

 2.2 in its length; interorbital greater than eye, 3.6 to 4.3 in head; 

 eye 3.4 to 4.8 in head; nose shorter than eye, 4.9 to 6.1 in head: 

 mouth small, more or less inferior, extending little back of front of 

 eye; maxillary 3.4 to 4.2 in head; lower jaw shorter than upper. Dorsal 

 fin about midway between muzzle and base of caudal, slightly behind ven- 

 trals, of 12 rays; last dorsal ray greatly elongated, extending past middle 

 of anal; anal rays 30 or 31 ; pectorals 1.2 to l.S in head; ventrals half way 

 to front of anal in adults. Scales S6 to 57, transverse series 23; no 

 lateral line; ventral scutes 19 (before ventrals) , 12 or 13 (behind ventrals) . 



This immensely abundant species, although little esteemed as a 

 food fish, is one of the most useful in our waters because of the al- 

 most exhaustless food supply which it offers to all the game fishes of 

 our larger streams and lowland lakes. Living itself mainly upon 

 food derived from the muddy bottoms of our very muddy rivers and 

 lakes, it serves as a means of converting this mere waste of nature 

 into the flesh of our most highly valued fishes. 



For this service it is especially adapted by the posession of a 

 very effective straining apparatus in its gills, by means of which it 

 separates the finest particles of silt from objects large enough to 

 serve it as food, and by the extraordinary development of its diges- 

 tive surface in a long and convoluted small intestine, thickly beset 

 with finger dike villi within, and with tubular casca without, each of 

 which is closed at its outer end and pours into the intestine through 

 its inner opening the digestive juices which it is the function of these 

 organs to secrete. The thick-walled muscular stomach, resembling 

 the gizzard of a bird — whence its name of gizzard-shad — is another 

 adaptation to a kind of food not available to most other fishes. 



It occurs throughout the Mississippi Valley, in brackish waters 

 along the Atlantic and the Gulf as far as Mexico, and in the streams 

 and lakes of the Mississippi Valley. In Illinois the gizzard-shad 

 inhabits all our larger rivers, together with the lakes connected with 

 them, sometimes ascending smaller tributaries during the season of 

 the spawning migration, and it has also made its way, by means of 

 canals, into lakes Erie and Michigan. In summer it is a rather 

 active fish, sometimes darting rapidly about in all directions and 

 often leaping out of the water. When surrounded by the seine, it is 

 likely to escape in schools by skipping lightly over the cork line. 

 In winter it withdraws largely to the deeper waters, where it hiber- 

 nates in a benumbed condition. 



We have found gravid females, and males running with milt, in 

 the central part of the Illinois River in May, and have seen speci- 



