BLACK BASS CULTURE 181 



=!ubmerged type, including both rooted plants and filamentous algiP, 

 and are usually so abundant that they must be removed before the 

 fish can be recovered when the ponds are drained in the fall. 



FERTILIZATION OF PONDS 



In Europe fertilizers have been used for a number of years to in- 

 crease fish production in ponds, especially in connection with the 

 rearing of carp {Cyprinus carpio) and the Schleihe {Tiiwa vul- 

 garis). Although we are concerned chiefly with other species of 

 fish, it may still be of interest to refer to some of the results obtained 

 by European investigators. Kuhnert (1909) reports that fertilized 

 ponds produce from 18 to 96 kilograms per hectare more carp than 

 ponds that were not fertilized. Experiments conducted during 1909 

 and 1910 confirmed the results obtained in 1908 (Kuhnert, 1910). 

 Hofer (1915), in a series of papers devoted largely to the discussion 

 of the effects of fertilizer on the chemical constituents of the water, 

 concludes that fertilizing the ponds increases fish production. 

 Czensny (1919) found that as a result of fertilizing the ponds the 

 total 1914 fish production was increased 28.2 per cent, carp produc- 

 tion alone was raised 35.7 per cent. Demol (1920) observed an ap- 

 preciable increase in fish production in 1919 at the Hofer Institute, 

 Wohlgemuth (1922) reporting on fertilizer experiments extending 

 over a period of seven years, 1915-1921, states that in every year the 

 fish production in the fertilized ponds exceeded that in the controls. 

 In 1918 and 1919 the increase in the fertilized ponds exceeded that in 

 the controls by more than 100 per cent. Fisher (1924) found that 

 the use of superphosphate at the Bavarian Pond Fishery Experiment 

 Station increased carp production from 20.8 to 22.9 kilograms per 

 2,000 m^ of water area. Walter (1925) on the basis of experiments 

 extending over a period of eight years states that with various phos- 

 phate fertilizers the fish production was increased by from 200 to 300 

 per cent. The same writer (Walter, 1927) reports that in 1926 the 

 increase in fish production resulting from the use of fertilizers 

 amounted to 61 Irilograms per hectare in one instance. The idea that 

 fertilizing fishponds is an economically sound practice seems to be 

 fairly generally accepted among fish-culturists in Europe. 



While European fish-culturists agree that the addition of ferti- 

 lizers has a beneficial effect on fish production, there exists among 

 them considerable difference of opinion as to what elements should 

 be supplied through the fertilizer. Their experimental work has 

 centered chiefly around the three elements — potassium, phosphorus, 

 and nitrogen. When all three elements are present in the fertilizer, 

 the fertilization is spoken of as complete; when only one or two ele- 

 ments are added, it is called partial fertilization. The partial ferti- 

 lization with potassium alone seems to have very little effect on pro- 

 duction. This conclusion is almost unanimous. Partial fertilization 

 with phosphorus, however, has produced large increases in produc- 

 tion. This is shown by Kuhnert (1909), Czensny (1919), and espe- 

 cially by Fisher (1924) and Walter (1925). Czensny (1919) obtained 

 interesting results when fertilizing with phosphorus and potassium; 

 namely, the fish production was much less when both potassium and 

 phosphorus were used than when the latter was used alone. Czensny 



