PLANTS IN PONDFISH CULTURE. 13 



by seining during the breeding period, but the large size of the 

 fingerlings (Table 5) at the date recorded seems worthy of note and 

 readily explainable in terms of an abundance of desirable natural 

 food. 



The succession of causes, physical and physiological, which have 

 led to the remarkable acceleration of growth in tlie alga, Aphani- 

 zomenon, and the accompanying culture of daphnids is not easy to 

 explain ; yet it is desirable to record the method of treatment of the 

 pond which has produced this extraordinary development. The pond 

 covers an area of 0.66 acre and is free from floating plants. In the 

 shallow portions there are submerged aquatics such as Naias and Pota- 

 mogeton pusUlus; and around the edge, a little of the blanket-form- 

 ing alga, Cladophora crispata. In general it is an open pond free 

 from the larger aquatics or their accumulations. It could easily have 

 become " seeded down " by spores of Aphanizomenon through inlet 

 waters from the supply reservoir which in turn receives the river 

 water. This alga is common in the supply waters and is distributed 

 in season to the ponds. Daphnia pulex are also connnon in the ponds. 

 A contributing cause of the great " wave " of Daphnia is possibly 

 due to the fact that the pond has been wintered dry during successive 

 seasons, the freezing and drying processes affecting the winter eggs 

 of the daphnids beneficially. 



MAYFLIES IN THE FOOD OF BASS. 



Reference to Table 2 indicates the importance of mayfly larvae in 

 the food of the young largemouth black bass. The mayflies are 

 herbivores. The researclies of Needham (1905), Morgan (1913), 

 and Clemens (1917), on the life histories of these insects have shown 

 that they subsist on a variety of plants in our lakes and streams, the 

 familiar articles of diet being diatoms, unicellular and filamentous 

 algse, and the larger aquatic plants, the latter generally in a partial 

 state of disorganization. Unfortunately, time has not permitted in- 

 vestigation of the plant associations of this group of insects in 

 small ponds. From the few records of examination, however, it may 

 be forecasted that an important habitat preference of some species of 

 the larvae is among the larger potamogetons. 



THE DIRECT FUNCTION OF PLANTS IN FISHPONDS. 



The tables show a forage value of plants which can not be regarded 

 as merely accidental. By reference to Table T it becomes evident that 

 the young of the buffalofish favor an admixture of animal and plant 

 substance. The absence of grit in the digestive tract and the presence 

 of plant materials, such as the staminate flowers of Elodea, for ex- 

 ample, which are found only at or near the surface of the ponds, illus- 

 trate the wide range of their feeding habits. The high percentage 

 in the food content of the flagellate plants, Pandorina, Eudorina, and 

 Pleodorina, is suggestive of the value of the small things among the 

 pond plants. 



The most conspicuous function of plants in the fishpond is found 

 in their indirect relations, in their contribution to the forage of 

 myriads of animal forms upon which fish feed. This paper has 

 emphasized this function of plants in its consideration of animal- 



