2 U. S. BUREAU OF FISHERIES. 



the young, and therefore the pond is the direct object of attention 

 in order to produce the maximum number of fish. Fish culture 

 under these conditions is consequently intensive pond culture, and 

 in the United States the term " pond culture " distinguishes this 

 branch of fish culture from the propagation of all fishes whose eggs 

 can be expelled and fertilized artificially or which are incubated in 

 hatching houses by the use of special apparatus and equipment. 

 The species to which it is ^applied are chiefly the black basses, 

 crappies, sunfishes, and catfishes. 



The propagation of the Salmonidae, notably the trouts, approaches 

 pond culture in the fact that several species are often reared in 

 ponds, whereas the other fishes hatched in special equipment are 

 usually distributed as fry as soon as the yolk sac is absorbed. How- 

 ever, although the cultivation of the trouts in this country may re- 

 quire ponds in which to rear the young, the different service the 

 ponds perform and the different management required place Ameri- 

 can trout-rearing methods outside the proper definition of pond cul- 

 ture.^ In Europe the case is not wholly similar ; although in a few 

 instances American methods have been adopted, the term " pond 

 culture " usually embraces the rearing of trout by much the same 

 methods as are in the United States pursued only with fishes that 

 can not be artificially spawned; that is, the young trout may not 

 be fed artificially but often subsist in large part upon the natural 

 food supply induced by culture of the ponds. 



IMPORTANCE OF AQUATIC PLANTS IN POND CULTURE. 



Since the young of the species of fishes to which pond culture is 

 applied in the United States can not be successfully confined in 

 the troughs or small ponds of the American trout breeder and do 

 not accept artificial food, they must depend for sustenance upon 

 minute forms of animal life found in the waters and upon one an- 

 other. At a very tender age they develop cannibalistic tendencies, 

 and even where there is apparently an abundance of natural food 

 they may reduce their own numbere 60 to 80 per cent within a month 

 or six weeks from the time of hatching. It is therefore necessaiy 

 in pond culture to provide not only sufficient natural food to satisfy 

 the physiological requirements of the young fish, but, so far as pos- 

 sible, an abundance that will divert them from the tendency to 

 devour one another. 



2 It may not be amiss here to point out the distinction, between trout culture by 

 American methods and pond culture proper by reference to the procedure and the con- 

 ditions at an American trout hatchery. Trout are not dependent upon natural food and 

 do not require a natural environment. It is customary to rear them in wooden troughs 

 or in small rectangular ponds of earth, wood, or concrete, through which there is a con- 

 stant flow of water containing no visible plant or animal life. The water supply may 

 come directly from a spring or from an artesian well. At many of the most successful 

 commercial trout establishments in the United States the troughs and rearing ponds are 

 supplied with water from artesian wells from 25 to 100 feet in depth. As the daily 

 feeding of a large number of flsh in a confined area necessitates frequent cleaning, any 

 seeds or spores of vegetation introduced by the water supply have little or no oppor- 

 tunity to obtain a foothold. The trout fry will eat artificial food from the time the 

 yolk sac has been absorbed, and by a judicious arrangement of troughs, tanks, or small 

 ponds the trout raiser can maintain a very large number of flsh within a comparatively 

 small compass until they are of satisfactory size for distribution or for market. His 

 dependence is artificial food or the artificial introduction of natural food, and without 

 these means he would be powerless to conduct operations on an extensive scale. In 

 American trout culture aquatic vegetation, so essential in pond culture, is but a negative 

 factor. 



