6 PLANTS IN PONDFISH CULTURE. 



young fish. An inventory (Table 1) was taken of the plant popula- 

 tion in certain ponds,'^ covering all forms, the larger rooted aquatics, 

 the floating forms, including the filamentous algae, and the plankton. 

 Simultaneously with the inventory an examination was made of the 

 food found in the digestive tracts of the young fish taken from the 

 ponds at regular intervals. By this means it has been possible not 

 only to identify the food but to determine the character of the forage 

 grounds of the fish and to consider the various plants and the animal 

 associations of importance in the economy of the pond. 



Collections of fish were made at weekly intervals and, if not ex- 

 amined at once in their fresh condition, were kept in an alcohol- 

 formalin preserving fluid until needed. In examining the food the 

 method of Peai-se (1918) was employed, that is, the food content of 

 the digestive tract was pressed out upon a glass slide, moistened, 

 and examined under the dissecting and compound microscopes. All 

 figures in the tables referring to food content represent volumetric 

 percentage estimates. Measurements in lengths are given in milli- 

 meters and exclude the caudal fin. 



A brief and general description of the ponds under investigation 

 will assist in making the interpretation. The accompanying map 

 from an earlier publication of the Bureau shows clearly the position 

 and arrangement of the ponds at the Fairport station. They are 

 gi'ouped in six series, A, B, C, D, E, and F, respectively, the ponds 

 in each series being numbered independently. The investigations 

 here recorded were concerned only with series B and D, the former 

 composed of six small, the latter of nine somewhat larger dirt ponds. 

 The areas of the specific ponds studied, that is, 16B and 1,2, 3,8, and 

 91), vary from 0.22 to 0.85 acre. Water is supplied to each 

 through inlet pipes connected Avith a large reservoir, which in turn 

 is supplied from the Mississippi River. The depth varies from 

 about 6 inches near the inlet pipes to 7 or 8 feet at the outlet. Plants 

 common to the ponds of the region have been introduced; marsh 

 plants such as cat-tails, Sagittaria, Bidens, and Eleocharis occupy 

 the shallower portions; sedges bind the borders of the deeper por- 

 tions; and floating and rooted aquatics flourish within the pond 

 area. Various aquatic insects and other animal forms have found 

 their way into the ponds, and practically natural conditions prevail. 



BASS, CHIRONOMID, AND ALGAL RELATIONS. 



It is shown in Table 2 that the chironomid larvae are among the 

 most important single items of food taken by the young of the 

 largemouth black bass during the summer. The larvae of a certain 

 species of the chironomids removed from the digestive tract were 

 identifiable and later checked up with specimens taken from the ponds. 

 These proved to be Orthocladius nivorkmdus Fitch., a species com- 

 mon in the ponds and the one upon which the bass chiefly fed. The 

 body walls of this larva are thin and transparent, and when lightly 

 crushed under a cover glass the food content can be readily deter- 

 mined with the microscope. It was this identification of the alga 

 in the crushed specimens taken from the bass that gave the clue 

 to the chain of food relations subsequently to be described. 



" See accompanying map showing topography of the ponds under investigation. 



