tary. Schaeperclaus (1933) treated the important physical factors in pond 

 culture^ particularly depth. He established optimum depth for assinilative 

 plant functions at 1 to 2 meters., since shallower areas fluctuate readily in 

 temperature and oxygen content, Schaeperclaus further pointed out the in- 

 creased nutrient release from bottom soils per unit water volume in shallow 

 waters, and in ponds with large shore development „ Rounsefell (19U5) in- 

 dicated a straight-line logarithmic relation between fish productivity and 

 size of water bodies | smaller lakes had the greater yield per unit area. 

 Rate of water exchange was considered by Schaeperclaus (1933) ^ Lawson (1937), 

 Ifiesner (1937) ^ and others, who concluded that a small exchange is usually 

 necessary for temperature and oxygen control, but that a large outflow re- 

 moves nutrient materials „ Nutrients may also be lost by seepage or by 

 settling through sandy or rocky bottom tyr^es, which are noticeably unpro- 

 ductive (Lawson, 1937j Province of Quebec, 19h3) , Many authors discuss 

 light and heat requirements as affected by shade and turbidity of the water. 



In all waters, light and heat are the physical essentials for photo- 

 synthetic activity which, in turn, is basic to productive capacity. Water 

 temperatures, in general, depend upon climate, sunlight, and depth, 

 Probst (1950) found an avera^^e increase in carp ^deld of 22 kilograms per 

 hectare for each 1* C rise in mean temperature in unfertilized oonds over 

 a period of 32 years. Light intensity and penetration are affected by 

 border vegetation, floating aquatic plants, and turbidity. The latter may 

 be caused bj/ plankton blooms., silt, particulate organic matter, or by pig- 

 ments and suspensoids as in bog waters. Excessive turbidity, according to 

 Smith (i93lja), has a pronounced effect in confining ddily heat gains to 

 the surface layer of water. Plankton turbidity, while often indicative of 

 oroductive waters, limits heat and light penetration, thus reducing the 

 depth and effective volume of the trophogenic zone. On the other hand, 

 such turbidity aids in the control of soft water flora (Surber, 19U8^ 

 Swingle and Smith, 19^0) and improves angling success (Smith and Swingle, 

 19h3) - Excessive shade caused by aquatic plants is a similar hindrance 

 to heat and light exposure of the water and results in lowered production 

 ('.fiesner, 1937). Temperatures, optimum for growth of the desired fish 

 species, plus time give the grovdng season which is also relevant to fertil- 

 ization. Lastly, water movement can be added inasmuch as it affects the 

 distribution of heat and nutrient materials viathin the environment. 



Generalizations may be drawn concerning the physical characteristics 

 of waters vjith respect to fertilization; 



1, Dimensional increase of the environment (beyond that of the 

 highly productive culture pond) decreases its possibility for 

 successful fertilization. This limitation involves economical 

 impracticability, lack of control and manipulation, and chemi- 

 cal-biological complexities which will be considered in the 

 following text, 



2. Increasing depth decreases the relative productive potential. 



