WHITE SUCKER 
179 
Feeding is most continuous on bright warm days. The fear of being exposed 
to view, which seems such a powerful instinct in the adults, does not prevent feeding 
in shallow places in the daytime during the first summer; but after the first winter 
suckers are inhabitants of the deeper places in the stream, except at night or during 
their migrations. 
The food of 57 specimens of this stage was examined with the following results : 
Percentage 
Chironomid larvte and pupae 28 
Diatoms and desmids 22 
Rotifers 4 
Entomostraca 3 
Protozoa (Difflugia) ____ 9 
Algae 2 
Fragments of arthropods 1 
Sand 21 
Unidentified (largely mucus) 10 
Total 
Animals 
Plants 
Sand 
Unidentified 
45 
24 
21 
10 
This is virtually identical with the diet characteristic of the critical period. 
There is no item of food taken near the surface which is not also found at the bottom, 
whereas sand is taken only at the bottom. 
The striking facts here are that up to 3 inches in length (2 years) the sucker con- 
tinues to be limited to microscopic matter and that the indigestible sand is not elimi- 
nated from the diet. The habit of almost continuous feeding (by day at least), and 
the fact that the alimentary canal is seemingly never empty become intelligible 
when we consider how little of the matter eaten is actually available to the fish as 
nourishing food. The following is an attempt to estimate the nonnutritious waste 
matter: 
Percentage 
Sand 21 
Protozoa (shells of Arcella and Difflugia) 5? 
Entomostraca (chitin) 2? 
Rotifera (chitin) 2? 
Diatoms (silicon) 10? 
Chironomids (chitin) 12? 
Total. 
52 
This estimate may be far from exact, but it is not without significance. 
To test whether suckers can, after the critical period (17 millimeters), catch 
floating organisms in sufficient quantity to maintain life, a number (12 to 15) of 
them, measuring 22 to 25 millimeters, were placed in a hatching tray with screen 
bottom and ends. This was set in one of their favorite haunts but 8 inches off the 
bottom. For a control, dace of equal size were placed with them. The latter sur- 
vived well upon particles floating in through the screening of the ends and bottom 
of the tray, but the suckers all died within eight days (two in five days). Examina- 
tion showed the alimentary canal to be nearly empty (a few diatoms only), and the 
fish were very thin. 
