40 U. S. BUREAU OF FISHERIES 



in the diet of the bullhead apparently did not depend on the depth 

 of the water but upon other factors discussed elsewhere in this paper. 



INFLUENCE OP ENVIRONMENT 



In many places bullheads are looked upon as scavengers of unclean 

 food habits. This is mainly because in those localities unclean animal 

 wastes are dumped into the water. As noted in the introduction, 

 Porbes and Richardson (1920) found distillery slops making up a 

 part of the diet of the bullheads they examined from Wisconsin 

 lakes. The type and quantity of the vegetation in the water in- 

 fluence the insect life, the crustaceans, and in like manner the kind 

 of food taken by the fish. Pollutions of the sort just mentioned tend 

 to kill the clear-water vegetation and to drive out the forms of 

 animal life dependent upon it. Under these conditions bullheads 

 liave no choice of foods but must take what they can get. This 

 study shows that there is such a slight variation in the environment 

 of the lakes of eastern South Dakota that it does not affect the 

 diet of the bullheads materially. 



The evidence gained from the investigations described would 

 indicate that as long as our South Dakota lakes are kept clean 

 (that is, not allowed to become polluted with refuse, sewage, and 

 trade wastes) the bullheads in these lakes will continue to be of the 

 same fine quality enjoyed at present. 



INFLUENCE OF SEASON 



The season of the year influences the food available to the bull- 

 liead to a marked degree. Nearly all the vegetation in these lakes 

 is of the annual type — that is, it dies in winter. To the present 

 time no study has been made of the food consumed by bullheads in 

 the fall and winter seasons. 



The first fish obtained for this study were taken at Lake Andes 

 on June 18, 1926. Besides chironomus larvae and pupae, these fish 

 were found to have eaten damsel-fly nymphs, Mycetobia larvae, and 

 the merest trace of plant material. At this season water plants were 

 just beginning to appear. At Poinsett, 3 weeks later, vegetation 

 was very abundant, and examination of specimens showed that one- 

 fourth of the diet of these fish was composed of plant tissue — Chara, 

 Spirogyra, Ruppia, and (Edogonium. Insects, their larvae, pupae, 

 and nymphs, and crustaceans were of greater variety. There were, 

 besides the forms already named for Lake Andes, Amphipoda, both 

 Gammarus and Hyalella, bivalves, Corixidae, Diptera, dragon flies, 

 Ephemeridae nymphs, Nais,Ostracoda, Sisyra, snails, and Trichoptera. 

 A small amount of clam flesh had been eaten by one fish, and two other 

 specimens contained a few fish eggs and fish scales. Fish taken from 

 Lake Kampeska on July 7 and from Lake Cottonwood on July 10 and 1 1 

 Iiad eaten about the same foods as had those taken earlier in the sea- 

 son, with the addition of the plant form, Chaetophora, beetles and beetle 

 larvae, and Cyclops viridis. The last catch of the season was at Lake 

 Oakwood on August 11, 1926. There was little change in the diet of 

 the bullheads in the various lakes during the intervening weeks. 



