AQUATIC PLANTS IN POND CULTURE. 19 



ducing algae, but it has been generally recognized by fisli-culturists 

 that spirogyra is an oxygenator. Further investigation may show 

 that all of the algae contribute to the sustenance of young fish. The 

 recognized food-producing value of some species of algae suggests 

 great possibilities in supplying food to the young fish during the 

 first two or three Aveeks, and especially so at pond-culture stations 

 like the one at Bullochville, Ga., where the water is so soft that it 

 has been difficult to maintain an adequate amount of plant life. A 

 definite knowledge of the relations of all of the various species of 

 algae to fish production is much to be desired. 



METHODS OF CONTROLLING AQUATIC VEGETATION. 

 ELIMINATION OF UNDESIRABLE PLANTS. 



Plants that are in themselves objectionable should, of course, be 

 eliminated for all time. There is, however, no known method of 

 eradicating the higher forms of vegetation from ponds without de- 

 stroj'ing the fish, unless it be possible first to draw off the water. 

 When this is done, certain forms of plants die from exposure and the 

 roots of others can be grubbed out. Cat-tails have a root stalk habit 

 of growth. If the plants are constantly cut, the root stalks will be- 

 come weaker and weaker due to the loss of the food manufacturing 

 leaf surface. If constant cutting is persisted in, the root stalks will 

 starve out after two seasons. 



In view of their recently recognized importance as food pro- 

 ducers, it may be assumed that, until seining operations commence, 

 the presence of certain species of algae will be encouraged, and that 

 in fishponds generally the removal of algae will not be attempted 

 until after the young of basses or sunfishes are a month old. How- 

 ever, there are times and places where it is desirable to destroy the 

 more obnoxious forms, and this may be accomplished by means of 

 copper sulphate, according to the method of Moore and Kellerman 

 for the disinfection of municipal water supplies.^ This method has 

 been successfully adapted, not only to pond culture but also to waters 

 containing trout, as is set forth in a report of experiments at the 

 "S^Hiite Sulphur Springs station of the Bureau of Fisheries.^ The 

 latter application of the method is of especial interest, for the reason 

 that trout are more than ordinarily susceptible to the toxic prop- 

 erties of copper. 



CHECKING SUPERABUNDANT OR UNDESIRED GRO\\T7I. 



To prevent superabundance of some vegetation or to make less ob- 

 jectionable the presence of troublesome species that can not be eradi- 

 cated, it is sometimes desired to check the growth of the plants. Mr. 

 Kellerman states, in a letter, that in water not unusually hard the 

 waterweed {Philotria canadensis)^ Chara, and several species of 

 Potamogeton may be considerably checked in growth by treating the 



•Moore and Kellerman: Copper as an Algicide and Disinfectant in Water Supplies. 

 Bulletin 70. P.ureau of Plant Industry, Department of Agriculture. (See p. 12.) 



' Mar.sh and Uobin.soii : The Treatment of I<Msh-Cultural Waters for the Removal of 

 Algae. Bulletin, U. S. Bureau of fisheries. Vol. XXXVIII, 1908 (1910), part 2, pp. 

 871-890. 



