324 FISHES OF ILLINOIS 



This remarkable species, particularly interesting because of its 

 food and feeding structures, and because also of the peculiar grunt- 

 ing 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 Missis- 

 sippi at the mouth of Rock River and the Illinois 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 coeffi- 

 cient 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 sheepshead, 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 commonly dressed and sold. It reaches a 

 large size, specimens of fifty to sixty pounds' weight being not un- 

 common. 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, pharyn- 

 geal 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 sometimes found in the food. 

 Half-grown specimens feed largely on aquatic insects, especially the 

 larvas of May-flies, mingling larger and larger proportions of mol- 

 lusks 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 vibrationsof the wall of the air-bladder caused 1 >v the contraction 



