324 FISHES OF ILLINOIS 



grunting noise which it sometimes makes, is one of the more 

 abundant larger species of our principal rivers and lakes. It has 

 been taken by us in 72 collections, ranging from the Ohio at 

 Cairo to the Mississippi at the mouth of Rock River and the Illi- 

 nois at Ottawa. Two collections have come from the Saline 

 River and from a branch of the Big Muddy in southern Illinois. 

 Most of the others are from the Illinois or the lakes of its bottom- 

 lands. Like the two preceding species, this predominates in 

 central Illinois, our frequency coefficient for which is 2.05. 



It is generally distributed throughout the Great Lake basin 

 and the Mississippi Valley between the Alleghanies and the 

 western plains, ranging from Lake Champlain to the Red River 

 of the North, and through the Ohio basin to Alabama, Louisiana, 

 Arkansas, Texas, and Mexico. 



In the Ohio Valley, in the South, and to some extent on the 

 Illinois River, it is known and marketed as the white perch. In 

 the Great Lake region it is more commonly called the sheeps- 

 head, and this is perhaps the name by which it is best known 

 in Illinois. Gaspergou is a name used for it in the southern 

 territories formerly occupied by the French. Thirty years ago 

 the sheepshead was universally rejected by Illinois fishermen as 

 worthless, but at the present time all except the largest are com- 

 monly dressed and sold. It reaches a large size, specimens of 

 fifty to sixty pounds' weight being not uncommon. It becomes 

 tough and strong with age, but is at its best when weighing from 

 three quarters of a pound to three pounds. The market catch 

 of sheepshead from the Illinois River in 1899 was 459,580 

 pounds. This fish is of a sluggish habit, living on the bottom of 

 muddy waters, where it feeds especially on mollusks, the shells 

 first being crushed by the powerful, paved, millstone-like, 

 pharyngeal jaws. Often the stomach contains only the soft 

 bodies and opercula of gastropod mollusks, the crushed shells 

 evidently having been thrown out. Crawfishes are also some- 

 times found in the food. Half-grown specimens feed largely on 

 aquatic insects, especially the larva? of May-flies, mingling larger 

 and larger proportions of mollusks with this food as they increase 

 in size, until they come finally to depend almost wholly upon 

 water-snails and the relatively thin-shelled clams. 



The peculiar grunting sound made by this fish when caught, 

 and also often heard as it moves about under the water, is 

 probably due to vibrations of the wall of the air-bladder caused 

 by the contraction of special " grunting muscles" — an apparatus 



