182 
BULLETIN OF THE BUREAU OF FISHERIES 
In the aDOve table is presented a comparison of the constituents of the diet 
during the three principal periods. The figures given are percentages of the volume 
of the food, and it is important to bear this in mind in obtaining a picture of the role 
played by the sucker as a consumer. The number of chironomids eaten is enormous. 
It was estimated that one sucker, 5 inches long, contained 1,200, and in addition 
to this 800 caddis-fly larvae and 60 May-fly nymphs were eaten. A daily ration of 
1,200 chironomids means that 36,000 are consumed in a month, or 216,000 in six 
months. 
It is possible to suggest some reasons that may account for the three following 
periods in the feeding habits — namely, the yolk-food period, the top-feeding period, 
and the bottom-feeding period. 
The first is obviously determined by the amount of food stored in the egg when 
laid. Factors external to the egg, such as temperature, will determine the rate of 
development of the larvae, and hence the length of time before the yolk is exhausted. 
The top-feeding period presents a greater problem. The air bladder is relatively 
very large at this time, and up to a length of 14 millimeters it is connected to the 
gut. It may be that control of the gaseous content of the air bladder is not possible 
to the fish during this period, and that they are actually unable to submerge them- 
selves below a depth of 6 inches. 
Bottom-feeding is related to the metamorphosis of the mouth, but implies also 
that the content of the air bladder permits swi mm ing at lower levels. 
The separation of sand from insects, etc., and its elimination before the insects 
are swallowed may be merely a matter of the relative size of food and sand. As 
long as the food consists of microorganisms it can not, apparently, be separated 
from the sand; but when such insects as caddis-fly larvae are taken they are held in 
the mouth. while the sand is ejected. The following organisms were identified in the 
food of the white sucker (210 specimens): 
Algae: 
Mougeotia. 
Spirogyra. 
Desmids: 
Closterium. 
Cosmarium. 
Diatoms: 
Gomphonema. 
Diatoma. 
Cymbella. 
Navicula 
Surirella. 
Nitzchia. 
Epithemia. 
Stephanodiscus. 
Fragilaria. 
Protozoa: 
Difflugia. 
Arcella. 
Euglena. 
Copepods: 
Cyclops. 
Canthocamptus. 
Cladocera : 
Chydorus. 
Scapholeberis. 
Alona. 
Alonella. 
Daphnia. 
Eurycercus. 
Ostracoda: 
Gypris. 
Cypridopsis. 
Malacostraca: 
Gammarus. 
Cambarus (fragment only). 
Rotifera: Various species. 
Nematoda: Ascaris (?) 
Annelida: Setae only. 
Mollusca: Sphaerium (?). 
Cestoda: Proteocephalus (?). 
Trematoda: Crepidostomum (?). 
Insecta: 
Chironomid larvae and pupae. 
Chironomus. 
Tanytarsus. 
