AQUATIC PLANTS IN POND CULTURE. 3 



Through the necessity for natural food, then, comes the primary 

 importance of aquatic plants in pond culture. All animal life is 

 dependent, directly or indirectly, upon plant life, the minute forms 

 as well as many of the larger feeding directly upon plants, and the 

 herbivorous species in turn serving as food for the carnivorous. In 

 the beginning the young fishes feed upon water lice, nymph larvae, 

 and other minute forms. As they develop in growth they feed upon 

 small crustaceans, insect larvae, and other forms that are not ordi- 

 narily abundant except in an environment with abundant vegetation. 

 Aquatic plants are therefore the food-producing agency in pond cul- 

 ture and are accordingly indispensable. It is also obvious that by 

 a judicious selection of j^lants the quantity of food can be maintained 

 at the maximum, with corresponding results in the production of 

 young fish. 



It is the consensus of opinion among pond culturists that plants are 

 essential also for the proper aeration of the water. At a trout hatch- 

 ery the fish are supplied with the necessary air by means of a con- 

 stant flow of water; in pond culture the volume of water supply is 

 often little, if any, more than enough to compensate for evaporation 

 and leakage, and the oxygenation from this source is limited. The 

 balanced aquarium is a well-recognized illustration of the value of 

 plants as oxygenators. Although there are many factors entering 

 into the aeration of the waters at a pond-culture station that do not 

 apply to the balanced aquarium, and it may be assumed that the 

 larger the body of water the more must other factors than those of 

 the balanced aquarium be considered, there can be no doubt as to the 

 role of vegetation in the aeration of shallow ponds of limited area. 



It is perhaps superfluous to add that submerged plants bind the 

 bottom soil together, thus acting as a deterrent to turbidity from that 

 source; and that plants doubtless facilitate clarification when the 

 water of a pond has become turbid with surface drainage after a 

 rain or from other external causes of a temporary character. As 

 an evidence of this the numerous reservoirs or " tanks " in the 

 West, which are devoid of vegetation and in which the water is 

 constantly roiled, may be cited. It is possible that in some instances 

 the absence of vegetation is due to the constantly roily water, a 

 condition elsewhere referred to; but control tests in aquaria dem- 

 onstrate that in an aquarium containing Cabomba the water is 

 clarified much more quickly than in one in which there is no vegeta- 

 tion. 



Some other advantages of aquatic plants that are of more or 

 less importance may be mentioned, such as shade, shelter from 

 predacious birds, and refuges for the smaller fishes from the larger 

 ones and from each other. The ornamental feature of some plants in 

 some places is of minor importance from the viewpoint of the 

 fish-culturist, but all of these have been given consideration. 



OBJECTIONABLE ASPECTS OF POND VEGETATION. 



Notwithstanding their essential importance in fishponds, however, 

 and the careful effort requisite to the securing of suitable vegeta- 

 tion, in one aspect nearly all aquatic plants are to the pond culturist 

 wholly a nuisance and a necessary evil. The seining of the ponds, 



