THE TREATMENT OF FISH-CULTURAL WATERS FOR THE 



REMOVAL OF ALG/E. 



By M. C. MARSH and R. K. ROBINSON, 

 United States Bureau of Fisheries. 



A great annoyance encountered at fish-cultural establishments, or in any 

 ponds where fish are held, is the presence in the water of mossy or slimy plant 

 growths consisting of forms known to botanists as different species of algae. 

 These appear usually as green or bluish green masses or strands of filaments, 

 which clog the screens of ponds and supply canals and accumulate in the ponds 

 themselves. The clogging of the intake screens or supply pipes endangers the 

 life of the fish by reducing or entirely shutting off the water supply, while the 

 clogging of the outlet screens prevents the water from escaping through the 

 proper channel and allows the pond to fill and overflow, carrying away the 

 young fish; in either case a loss of fish is likely to result, and the trouble of 

 frequent cleaning of screens is inevitable. This sometimes requires the regular 

 attention of the watchman all night or the special services of an extra laborer. 

 The formation and accumulation of algse within the pond containing fish, espe- 

 cially if there are fry or fingerlings, prevents proper feeding, greatly interferes 

 with the operation of nets in handling fish, and occupies valuable space. The 

 latter tends to crowding and retardation of growth, while frequently fry become 

 entangled in the filaments and strands of the algse in such a manner that many 

 are lost from this cause alone. 



It is true that the green filamentous algae which are mechanically so annoy- 

 ing are oxygenators in sunlight and often add materially to the amount of dis- 

 solved oxygen in the water. In ponds without a rapid circulation they have 

 been observed to superaerate the water with oxygen, and this sometimes occurs 

 in flowing streams;" that is, the algse add oxygen to water which already has 

 absorbed its full or normal supply from the atmosphere. Under these condi- 

 tions oxygen gas must have been passing slowly from the water into the atmos- 

 phere. The objectionable features of algse, however, usually far outweigh the 



oMarsh and Gorham: The gas disease in fishes, Report Bureau of Fisheries, 1904. p. 357. 1905. 



B. B. F. 1908— Pt 2—13 87 1 



