FOOD OF THE SHORE FISHES OF CERTAIN WISCONSIN LAKES. 28 1 



to earthworms and leeches. Some of the small fishes Qohnny darter, stickleback) show 

 little change. Others which attain larger size (crappie) are versatile and sometimes 

 feed as adults on the same foods used when young. The two fishes which are largely 

 vegetarian when adult (carp, sucker) both make their first food largely from entomos- 

 tracans, then change to insect larvae, and finally to plants. 



Though the data from which these conclusions are made are by no means full 

 enough to make very definite generalizations, the general course of events is indicated. 

 The most important foods for young fishes are entomostracans, insects and their larvas, 

 and amphipods. Forbes " discussed changes in foods correlated with increase of age fully. 



V. INFLUENCE OF FOOD ON THE SELECTION OF HABITATS. 



Shelford (1911a) said "An animal should be associated, first, with breeding condi- 

 tions; second, with the feeding conditions; third, with conditions affording shelter." 

 Of course no species of fish could persist in a body of water that did not have places 

 suitable for breeding. Most fishes during the breeding season give up feeding more or 

 less and become more bold, thus being less protected. If there must be a choice between 

 reproductive activities and something else, reproduction usually comes first. There is 

 considerable variation in the length of time during which breeding activities dominate 

 all others. Many species lay their eggs and take no more care of the young; some even 

 eat their own eggs or young. Other fishes look after the young until they are able to 

 shift for themselves. A cisco finishes its spawning in a few days; the young of the 

 dogfish are watched by the parents for a couple of months. Aside from, the actual 

 time spent in breeding, some antecedent activities are doubtless influenced by prepara- 

 tion for reproduction, but in any of the fishes discussed in this paper breeding and its 

 associated activities do not occupy more than a fourth of each year, usually much less. 



Reproductive activities are, then, transitory, but food and shelter are more or less 

 constant necessities. During the greater part of the year the dominant activity of a 

 fish is finding food, and habits of feeding play a considerable part in keeping fishes in 

 particular habitats. Any organism must have a continued supply of materials to 

 furnish substance and energy. If shelter is close to the food supply, so much the 

 better; but if it is not, food must still be sought. 



According to the data discussed in section II of this paper, the habitat that affords 

 the largest and most varied food supply is the aquatic vegetation along the shore, and 

 it also furnishes good shelter. More species of fishes frequent the shore vegetation than 

 any other habitat, and they together take a greater variety of food than those in any 

 other place. The habitat most favored by fishes next to the general shore vegetation 

 is the weedy mouths of streams; the third choice is sand and pebble beaches; the fourth, 

 rivers and small streams; and the fifth, the little weedy ponds along shore. The number 

 of fishes occurring in different habitats and their chief foods are shown in Table 6. 



The habitats having the greatest variety of food and shelter have the most species 

 of fishes. If there must be a choice between food and shelter, the former is taken. 

 For example, a pebble and sand beach has less shelter and more available food than a 

 rocky beach and is visited by five times as many species of fishes. Forbes (1888) has 

 discussed the dependence of the food of fishes on their structural equipment in a mas- 



o Forbes, S. A.: On Ihe food relations of freshwater fishes: A summary and discussion, pp. 492-497, 1888. 



