Part III.] Pond Fish Culture. 141 



bonic acid gas) and give off oxygen. Decaying matter in the 

 ponds uses up oxygen and gives off carbon dioxide, and grow- 

 ing plants take up the latter and use it in the manufacture of 

 plant food and new plant tissues, at the same time setting the 

 oxygen free once more for the use of both growing plants and 

 animals which use oxygen in respiration. Thus a pond that 

 is well stocked with growing plants that are good "oxygen- 

 ators," so to speak, has a chemical laboratory for using up 

 some of the products of this dead waste in the pond, and re- 

 liberating the life-giving oxygen. It is possible to have an 

 aquarium or a pond so stocked with growing plants that there 

 is an equilibrium in nature between life and growth on the 

 one hand and death and decay on the other ; and the water can 

 be kept in good condition for weeks or even months without 

 the addition of any fresh supply. Therefore it is not neces- 

 sary to have a stream of water running through a pond in 

 order to keep it pure and in good condition for fish. If the 

 original supply is good and is sufficient to offset the leakage 

 and evaporation, the water in such a pond can usually be kept 

 in very good condition by the use of growing plants. 



FEEDING FISH. 



This is a suljject that is continually being discussed by fish 

 culturists. Many factors, such as kind, size and number of 

 fish, enter into the problem, which must be solved under many 

 and varied conditions. Many trout culturists have the busi- 

 ness pretty well in hand as applied to the particular locality 

 and conditions they have to contend with. However, the whole 

 subject seems to be open for debate, amendment and further 

 consideration. 



Feeding Fish at the State Hatchery. 



What we have done along this line has been more in the way 

 of experiments for the purpose of finding out certain things 

 than to get actual results from any system of feeding. The 

 subject has been discussed at various places in this bulletin, 

 and especially in Part III, in connection with the consideration 

 of the habits and culture of each kind of fish. 



Feeding fish at the State Hatchery, where there are ninety- 

 nine ponds, is a proposition that can not be entertained except 

 on special occasions and in ponds where a number of fish are 

 being held for a definite purpose and for a definite length of 

 time. The fish that we most commonly raise, such as the bass, 

 crappie, sunfish, catfish and goldfish, can be fed with any avail- 

 able food suitable to their tastes. These fish soon learn to 

 come to places near the shores of ponds where food is thrown 

 to them. After the fish become accustomed to these feeding 

 places it is surprising how regularly they will appear for their 

 food, and how tame seme of them will become. 



