fertilizer effectiveness. Time, experimental design^ or nature of the 

 environment often necessitates the use of other indices » Moyle (19U9) 

 considered several such measures of lake productivityo Quantitative 

 determinations of plankton and bottom fauna^ creel returns, fish length 

 and- weight increment, relative plant growth, and plankton turbidity are 

 some biological evaluations » Changes in pH may be significant. Surber 

 (I9U7) and Zeller (19$2) suggested that an inverse relation exists between 

 water nitrate and fish growth, Meehean and Marzulli (19h5) contended that 

 huraus loss and C:N ratio of the substrate may demonstrate fertilizer effec- 

 tiveness. Their experiments indicated that lowest humus loss and highest 

 C:N ratios were associated with highest productivity. The authors concluded 

 that humus loss is more reliable, while CjN ratios were valuable because of 

 ease in determination. Many of these secondary indexes are valuable at times, 

 and occasionally necessary, but their reliability when applied to fish pro- 

 duction is questionable. The many variables in operation subject these 

 indexes to extreme critical evaluation. 



Wiebe (1929) described aquatic fertilization as "intentional pollution", 

 implying that it may cause unwanted or, perhaps, detrimental changes. 

 According to Hasler (19li7), fertilization involves eutrophication. Many 

 workers have experienced undesirable increases in vegetation, resulting in 

 higher water temperatures and oxygen depletion. Wiebe (I93I4.) pointed out 

 relations between oxygen content and temperature-flora conditions, indi- 

 cating that reasonable amounts of fertilizer \-jill not cause oxygen deple- 

 tion so long as vegetation is alive. Measurements for minimal oxygen 

 should be made at dawn (Hcgan _, 1933) ^ Smith (193lia) noted the extreme 

 chemical and physical conditions tolerated by lower organisms in heavily 

 fertilixed water. Swingle and Smith (1939a) found that ammorium sulfate 

 lowered pH values significantly in moderate to heavy doses „ while sodium 

 nitrate tended to increase the hj'-droxyl-ion concentration,. Certain elements 

 (Cu, Zn, As, etc.) are especially toxic to fish in soft waters, Wiesner 

 (1937) cautioned a,-,ainst the use of large amounts of fertilizers containing 

 toxic substances such as cyanide and ammonia. Undesirable effects of fer- 

 tilization are not limited to chemical toxicity and objectionable flora, 

 but mayresult from the growth of competitive fish or other injurious fauna. 



FERTILIZATION AND POND CULTURE 



Fertilization had become a part of Eurasian pond cultiire long before 

 it was accepted in this country^ This early development was stimulated by 

 extensive fish-cultural enterprises and their importance In Eiorasian 

 economy Therein is symbolized the basic difference in fish culture be- 

 tween the two continents. In Europe and Asia, the primary aim of aqui- 

 culture is to produce quantities of protein foodc Here, most cultural 

 efforts are concerned with a recreational fishgry. Tha European approach 

 to scientific pond fertilization has been meticulous. Consequently, gen- 



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