290 



Nutrients 



manures have been supplied to fish ponds in the Old World for cen- 

 turies, but in the 1930s the use of chemical fertilizers was begun on 

 an expanding scale in the United States. By broadcasting fertilizer, 

 such as "6-9-2" to "12-9-2," over the pond from the shore (Fig. 8.2), 

 or from a boat, the concentration of nutrients is maintained continu- 

 ously at such a level that phytoplankton can flourish through the warm 



Fig. 8.2. Broadcasting commercial chemical fertilizer over a pond in Belmont, 

 Mass., to supply nutrients to the phytoplankton at the beginning of the food chain. 



season of the year. The thick growth of planktonic plants provides 

 abundant food for copepods, cladocerans, and other types of zoo- 

 plankton and for the bottom fauna, among which chironomids are 

 particularly prominent. The resulting increase in the abundance 

 of these invertebrates stimulates the growth of fish such as the blue- 

 gill sunfish that feed upon them, and the enlarged population of 

 these "forage" fish furnishes a rich food supply for predatory species 

 such as the bass. In this way the production of pan fish or sport fish 

 in the pond is significantly improved (Edminster, 1947; Meehean, 

 1952 and succeeding articles in the Symposium on Farm Fish Ponds 

 and Management). Similar augmentation in the growth of marine 

 fish by the use of commercial fertilizer to stimulate the development 

 of phytoplankton and subsequent links in the food chain has been 

 demonstrated in Scottish sea-lochs (Gross, 1947; Raymont, 1950). 



