FOOD OF BULLHEADS 39 



FOOD HABITS 



The bullhead is referred to m general as a bottom feeder. It does 

 feed upon many forms of life at the bottom, it is true, but it has 

 also been seen to feed at the surface and at varying depths wherever 

 food is to be had. Food found in both the stomach and the intes- 

 tines of many specimens were grouped or sorted as to kinds, as 

 though the fish had eaten of one kind for a time and then passed 

 on to another. 



There was a greater proportion of vegetable matter in the intestines 

 than in the stomach. Examination of stomach contents revealed 

 the fact that the majority of the fish had taken into the stomach 

 proportionately larger quantities of animal food than plant food. 

 Even granting that the bullheads took equal amounts of plant and 

 animal foods, this would indicate that animal food was digested 

 early, probably in the stomach, and was absorbed rapidly upon 

 reaching the small mtestine. Very little food ever was found in the 

 duodenum. It passes through quickly into the lower part of the 

 small intestine. 



Quartz sand grains were present often. The question arises 

 whether sand particles are incidental to bottom feeding or are taken 

 for other reasons, such as aiding in digestion; data at hand do not 

 indicate. Some stomachs examined contained snails and bivalves^, 

 without sand and others sand and no snails and bivalves. 



RELATION TO SIZE 



Schools of fingerlings, usually accompanied by an old bullhead, 

 feed near the surface. At a short distance they resemble a dark 

 shadow on the water. Fourteen specimens, 1}4 inches in length, 

 w^ere taken in a minnow net at North Red Iron Lake the latter part 

 of July. Examination showed that the stomachs of these tiny 

 bullheads contained 42.1 per cent Cyclops viridis, 29 per cent young 

 Cladocera, 5.4 per cent Cladocera eggs, and some insect eggs, beetle 

 larvae, Amphipoda, colonial Protozoa, Trichoptera, and a trace of 

 plant tissue. 



Though of the same kinds, the animal forms eaten by these bull- 

 heads were younger and much smaller than those eaten by the adult 

 fish. The Cladocera were about one-half the size of those found in 

 the stomachs of the adult fish at Lake Cottonwood, and the Cyclops 

 viridis could be seen only under the binocular microscope. Larvse 

 were those that had riot attained full size. 



DEPTH OF WATER 



Bullheads are shore fish. Parent bullheads usually are found in 

 shallow, weedy water, and others in deeper water, though, as a 

 general rule, none are far from shore — in other words, not far from 

 the source of their food supply. The greatest depth recorded from 

 which specimens were taken for this study was 12 feet. Other 

 depths ranged from 12 feet at Lake Poinsett to 3 or 4 feet in Cotton- 

 wood, 13/2 feet in Sand Lake, and 1 foot in Lake Byron. 



Cladocera and chironomus larvse and pupae were found to have 

 been eaten by fish at all these depths and in nearly all the lakes. 

 Other forms w'ere common in a number of the lakes. Their quantity 



