24 UNIVERSITY OF COLORADO STUDIES 



the young of C. commersonii sucklii may be recognized and distinguished from the 

 young of C. griseus. It is interesting to note that similar lateral spots, four in 

 number, occur on juvenile specimens of Catostomus nigricans LeSueur, the Hog- 

 sucker of the Mississippi Valley, and often persist as rather distinct blotches on 

 the adult. 



Suckley's Sucker feeds upon algae and diatoms which taken together make 

 up a large portion of the slime on submerged stones, and upon small mollusks, 

 both bivalves and gastropods, insect larvae and small worms. In addition a few 

 adult insects and quantities of debris are taken. When opportunity offers the 

 freshly deposited eggs of other fishes are eaten. All of the food is such as may 

 be found on the bottom or on stones. In the spring suckers are quite active and 

 have been known to take the fly and other moving bait, and in this season they 

 occasionally include some of the surface insects in their food. The food of indi- 

 viduals was found to vary considerably with the habitat and many kinds of small 

 animals which had become water-logged and had sunk to the bottom were recov- 

 ered from sucker stomachs. The data concerning the stomach contents of nine 

 specimens follow: 



West Plum Creek, near Castle Rock, June 8, 191 2. From small streams with rocky bottom, the 

 stones of which were covered with green slime. 



200 mm., vegetable debris and algae, 99 per cent; one small bivalve, Pisidium sp. 



igo mm., vegetable debris and algae, 100 per cent. 



igo mm., vegetable debris and algae, 80 per cent; bivalves, Pisidium sp., 20 per cent. 

 Republican River, Wray, October 26, 1912. From small stream with weedy and muddy bottom, 

 in lowland about one hundred yards from the main stream. 



190 mm., algae, 100 per cent. 



180 mm., midge larvae and pupae, 75 per cent. Stomach not full. 

 Grape Creek, Canyon City, November 8, 1913. Rapid moimtain stream, rocks and bowlders 

 filling stream bed, the submerged stones being heavily covered with a brown slime of diatoms, 

 no shore vegetation. 



150 mm., diatoms, 100 per cent. 



250 mm., diatoms, 100 per cent. 

 Boulder Creek, near Boulder, July 25, 1912. Small stream, gravel bottom, shore vegetation and 

 vegetation in the water near shore. 



170 mm., small gastropods, Physa spp. and Planorbis spp., 50 per cent; vegetable debris, 



50 per cent. 



200 mm., vegetable debris, 50 per cent; small gastropods, Physa and Planorbis, 25 per 



cent; one Dytiscid beetle. Stomach not full. 



This sucker reaches the length of 2 feet, although it is an inhabitant of the 

 smaller streams as well as the rivers. Being a rapid swimmer it is often found 

 in irrigation ditches at a considerable distance from the streams supplying the 

 ditches. The shutting-off of the water in these leaves the suckers stranded in the 

 fields, hence the name "Irrigation Sucker," by which they are popularly known. 



The subspecies C. commersonii sucklii ranges through the western portions 

 of the western tributaries of the Mississippi, east of the Continental Divide. 



