AQUATIC PLANTS IN POND CULTURE. 7 



are accordingly indispensable. It is also obvious that by a judi- 

 cious selection of plants 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 

 also essential 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 suj)erfluous 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 ]3ond has become turbid with surface drainage after a 

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

 superintendent of the Tupelo, Mississippi, station, Mr. C. W. Burn- 

 ham, cites 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. It is possible that in some instances the absence 

 of vegetation is due to the constantly roily water, a condition else- 

 Avhere referred to; but control tests in aquaria demonstrate that in 

 an' aquarium containing Cabomha the water is clarified much more 

 quickly than in one devoid of vegetation. It is believed that if many 

 of the so-called '' tanks '' of the Western States now devoid of vege- 

 tation could be stocked with water plants, these would not only pre- 

 vent turbid water by binding the bottom soil together, but would 

 under certain conditions prove an aid to clarification. 



OBJECTIONABLE ASPECTS OF POND VEGETATION. 



Notwithstanding their essential importance in fish ponds, how- 

 ever, and the careful effort requisite to the securing of suitable vege- 

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

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

 to obtain the young fish for distribution to waters they are intended 

 to stock, or for other purposes, can not be accomplished while thick 

 plant growth is present to entangle the fish and interfere with the 

 operation of the seine, and there is thus a periodical necessity of clear- 



