174 American Fisheries Society 



three weeks by a flow of clean water and without sew- 

 age. After this preliminary period, the sewage is 

 admitted to the ponds and its purification begins. The 

 Crustacea and other plankton multiply tremendously on 

 this continuous influx of sewage which avails them as 

 an unlimited food supply. In turn the young fishes find 

 this minute life an abundant food suitable for their own 

 rapid growth. The many forms of both animal and vege- 

 table life which attain greater size are eaten by the 

 older fishes. The species most commonly utilized have 

 been the carp, tench and pike (Esox), but cat-fish, black 

 bass, a flat fish and even the rainbow trout were con- 

 templated as desirable food fishes which further experi- 

 ment might show to be susceptible to this new method 

 of fish culture. 



The effect of the purification process can be seen very 

 soon after the entry of the sewage. An appreciable 

 cloudiness is caused in the water about the inflow end 

 of the pond, due to the turbid sewage. This affects only 

 a small portion of the pond, the turbidity soon disap- 

 pears and the contents of the rest of the pond are clear 

 enough to show plainly the vegetation and other organ- 

 isms on the bottom. Progressively toward the outlet 

 the water is more and more relieved of its sewage char- 

 acter until the effluent is said to be potable. The series 

 of ponds and the disposal plant as a whole present a 

 sightly appearance and resemble any well conducted fish 

 cultural station. The process can not be said to involve 

 a nuisance. 



The purification process is rather delicately balanced 

 and its successful and continuous operation depends on 

 foresight and constant care. The various reactions are 

 interdependent and must proceed with reasonable quan- 

 titative adjustment to each other, without which a pre- 

 ponderance of any one is able to disturb the co-operation 

 of all. The most important index is the dissolved oxygen 

 in the pond water, and daily estimations by color tests 

 are made. Additional control is obtained by other 

 chemical and bacteriological tests carried out every two 

 weeks. The absolute and relative quantities of sewage 



