eral references such as Schaeperclaus (1933) and Wiesner (1937) contain 

 great detail on many phases of pond enrichment. Smith (1932b) considered 

 two cultural concepts of fertilization; (1) Production of zooplankton in 

 greatest possible amounts for removal and feeding to fish; (2) production 

 of food directly in rearing ponds and natural waters. Many early experi- 

 ments were conducted in accordance with the first conceptj mainly because 

 plankton are able to tolerate abnormal amounts of f ertilizer. This view 

 has been super SBded in recent years by the second concept, the direct 

 fertilization of fish ponds. 



The Pond and Enrichment Procedure 



Physical characteristics, such as depth, size, and bottom type, exist 

 optimally in the culture pond. Many environmental variables (vegetation, 

 rate of exchange, temperature, sunlight, nutrient loss, and population 

 composition and density) are controllable, often to a large degree. Regu- 

 lation of the inflow and outflow affects water temperature, oxygen con- 

 tent, and nutrient retention. Pond-draining facilitates complete crop 

 removal. Small size and shallowness permits effective seining and control 

 of emergent border vegetation. The latter, in turn, determines the amount 

 of direct sunlight reaching the water. For these reasons, a drainable 

 culture pond represents the ultimate in potential aquatic production. 



Advantages of f ertilizing such an environment were given by Wiesner 

 (1937) s it is less expensive than artificial feeding^ the resultant 

 natural feeding causes rapid growth and low losses due to disease and nu- 

 tritional deficiencies; fish can then tolerate grt^ater population densities. 

 The rearing of brood trout in fertilized ponds, Wiesner added, is uniquely 

 advantageous. Initially there is a plankton bloom upon which fry feed and, 

 as the season progresses, larger food organisms produced correspond to 

 changes in diet of the growing fish. Meehean (1933) further concluded that 

 large fish can be produced at earlier maturity, and the shortened growing 

 season saves space and overhead. 



Fertilizers are selected to suit the needs of the pond after considera- 

 tion is given to the quality of the water and bottom soil. Swingle and 

 Smith (19^0) recommended 100 pounds of 6:8:U and 10 pounds of sodium nitrate 

 per acre-application. Schaeperclaus (1933) suggested using 35 pounds of 

 phosphate (T^Or) per acre alone, or with h^ pounds of potash (KpO) ,. Wiesner 

 (1937) advised similar araounts of phosphate (l80 to 270 pounds of super- 

 phosphate per acre) as effective and economical. Surber (19li7) tabularly 

 listed amounts of some single inorganic fertilizers needed to prepare vari- 

 ous NsP:K combinations. A list of fertilizers and the papers in which they 

 were reported is given in the appendix. Fertilizers are spread over the 

 bottoms of drained ponds before spring filling. They are applied to filled 

 ponds by broadcasting from shore or boat over shallow areas. American 

 theory recommends periodic applications throughout the growing season at 

 intervals governed by temperature, plant growth, and oxygen conditions in 

 the ijater. This maj'' be each 2 weeks in spring and at monthly intervals 



17 



