Fish Population Adjustment 163 



the production of fish in ponds for commercial sale is limited. Most ponds 

 and artificial lakes are for sport fishing. 



The primary exponents of pond fertilization for the improvement of 

 sport fishing are located in the southeastern United States where soils 

 are often infertile. Swingle and Smith ^^^' ^"^ stated that fertilized ponds 

 in Alabama support 4 to 5 times as great a weight of fish as unfertilized 

 ones; and consequently, the former give mucli better fishing. They recom- 

 mended the use of 100 pounds of 6-8-4 ( N-P-K ) and 10 pounds of nitrate 

 of soda per acre of pond for each application, with a seasonal schedule of 

 8 to 14 treatments, beginning March or April and extending to September 

 or October. 



In Alabama such a fertilization program produces a "bloom" of plankton 

 algae that prevents the developm.ent of filamentous algae and shades out 

 any rooted submersed aquatic vegetation. It will not control water-lilies, 

 lotus, or spatterdock; but these may be killed by removing the leaves 

 several times during the summer. ^^^ The first leaf cutting should be made 

 early in June and later ones every three weeks until no new leaves appear. 



According to Swingle,^^^ the algae produced by inorganic fertilization 

 were largely genera of the Chlorophvceae: Scenedesmus, Ankistrodesnius, 

 Chlorella, Staiirastriim, Pandorina, Cosmarium, Chlamydomonas, Nan- 

 nochloris, Pediastrum, Coelastrum and others. Euglenophyceae were also 

 abundant and occasionally dominant. Dinophyceae were often present 

 but usually not in large numbers. The bluegreen algae, Coelosphaerium 

 and Microcystis, occasionally became abundant for limited periods. Varia- 

 tions in kinds of algae were observed in various types of ponds. 



Swingle recognized the competition between plankton algae and fila- 

 mentous algae for dominance. He stated that either 6-8-4 or cottonseed 

 meal applied in clear ponds in cold weather will stimulate the growth of 

 filamentous algae on the bottom which will rise to the surface and shade 

 out plankton algae. However, if these substances are applied when the 

 water is "warm," plankton algae will be produced. Most organic material 

 encourages the growth of filamentous algae unless it colors the water and 

 thereby shades the bottom. 



There is no question but that the application of balanced inorganic 

 fertihzers will increase the production of fish in a pond or lake by in- 

 creasing the phytoplankton and, in turn, the aquatic animals at various 

 trophic levels between the phytoplankton and fishes.'^ 



Not only do potassium, phosphorus, and nitrogen function as fertilizer 

 materials in an aquatic environment, but some other elements such as 

 manganese may produce chemical changes that release inorganic ferti- 

 lizers from insoluble chemical compounds in the substrate of a pond or 

 lake,^" giving an end eflFect similar to that obtained by direct fertilization. 



