buffer effect and pH of water; provides calcium for nutrition; 

 and aids in detoxification, amelioration, and nutrient release. 

 Correct stocking as to species composition and number is essen- 

 tial. Proper fertilization and accessory techniques usually 

 boost fish yields to 100 percent or more over unfertilized ponds. 



15. The numerous pond-fertilization reports duplicate or parallel 

 each other in many instances, but indicate two aspects of pond 

 enrichments Cultural fertilization deals strictly with produc- 

 tion of fish by varying the type^ quantity <, and rate of applica- 

 tion in order to arrive at consistently high yields. Experimental 

 fertilization considers intricate problems of hydro-chemistiy 

 and biota-nutrient relations which can be explained only through 

 careful experimental studies o 



16. Sport-fish yields from cultural efforts in this country, comparable 

 to the high production of food fish from fertilized Asiatic and 

 European ponds, cannot be expected. High cost of fertilization 

 and lack of assured success call for the d evelopment of better 

 enrichment techniques in our pisciculture. 



17. Farm fish ponds are not discussed in detail, to avoid repetition 

 of information considered elsewhere in the report. Since these 

 ponds are established for a recreational fishery and may not be 

 cropped properly, a question is raised about the practical value 

 of fertilization involving cost. 



18. As aquatic habitats increase in size and depth, they become more 

 complex and less practical to f ertilizeo The average fish yield 

 in lakes is only a fraction of that in culture ponds. Besides 

 dimensional drawbacks, features of lakes that discourage fertili- 

 zation are lack of control, established populations, nondrainabil- 

 ity, thermal stratification, and indefinite harvest. 



19. Conclusions drawn from 11 lake-fertilization trials indicate 



that fish may have benefited from enrichment in only three experi- 

 ments. Effects of fertilization were more pronounced on lower 

 organisms, especially single species of plankton. Stimulated 

 growths of waterflora have caused winterkill upon decay. Although 

 the fertilization of lakes has increased their productive capacity, 

 its practical success in terms of net fish yield to anglers is 

 doubtful. End effects of lake enrichment must be viewed cautiously 

 with regard to the many variables of the environment. 



20. Sport-fishing returns of lakes are not comparable in monetary 

 value to the yield of fish flesh in pond culture. Lake fertili- 

 zation, at present, can be a method of studying water metabolism 

 with results possibly applicable to a future program of enrich- 

 ment that would raise the productive capacity of some lakes. If 

 clear-cut, significant data are to be obtained, such scientific 

 studies need sound experimental design. 



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