FEEDING FISH 215 



IX. Feed for Fish 



Among the cultivated or artificially reared food fish, the carp is the 

 most important. It is used as the basis in the following discussion. 

 Fish feeding is conducted along two distinct lines : 



A. Indirect feeding, or so-called "fertilization," which has for its 

 object the providing of favorable conditions, including food material, for 

 the growth and development of the forms of life which constitute the 

 natural food of fish, or, to go a step farther, to provide these condtions 

 for the still lower forms of life upon which the latter are dependent. 



B. Direct or artificial feeding, as for instance, supplying lupines or 

 fish meal, which are consumed directly by the fish. 



A. Fertilization 



The object of fertilization is to favor or encourage the development 

 of the natural animal or vegetable food material. 



1. Plankton, or pelagic life, constitutes a very important group of 

 these natural foods. For practical purposes this is divided into two 

 subgroups. 



Group 1. 



a. The lower plants, of which the most important representatives are: 

 a^. Bacteria, which, as everywhere in nature, live on waste animal 



and vegetable matter, convert it into carbonic acid, water and ammonia, 

 which in turn serve as food for algas and higher plants. Bacteria also 

 serve as food for Infusoria and similar minute forms of life. 



b^. Algce. — These are the most important oxygen generators in the 

 water, and, like the bacteria, serve as food for low, minute forms of 

 life. Among this group the common green fresh-water algse are the 

 most common. They occur on the bottom of ponds in long, thick masses 

 of interlaced threadlike forms or entwining higher plants. The gases 

 which they liberate tend to raise them to the surface in the form of 

 brownish layers or scum. The diatoms should also be mentioned here. 

 They are unicellular algas with a delicate silicious covering. Large 

 masses of bacteria live on the surface of the algae and serve in their turn 

 as food for Infusoria, etc. 



b. Infusoria, Amebce and Rotalia. These live on bacteria and them- 

 selves serve as food for higher forms. 



Group 2. 

 a. Small Crustaceans, or Entomostracans 



a^ Daphniidce, Daphnids, or water fleas, characterized by their mar- 

 velous power of reproduction (according to Rahmdohr one individual 

 may produce one thousand million oflFspring in 60 days). In the spring 

 of the year the single hard-shelled winter tgg hatches into a female, in 

 the dorsal brood organ of which a large number of small fertile sum- 

 mer eggs develop in the course of two days. In a few days the latter 



