OPERATING THE HATCHERY 



ter to kill the diseased fish, disinfect 

 the ponds, and start over with 

 healthy stock. 



In case of an outbreak of a disease 

 in one part of a hatchery, the in- 

 fected part should be isolated and 

 quarantined. All of the equipment 

 used in this part of the hatchery 

 should be disinfected. Ponds, also, 

 should be disinfected as soon as the 

 fish are removed. 



Disinfecting equipment 



For disinfection of tools and 

 utensils, any good disinfectant can 

 be used. Chlorine in the form of 

 hypochlorite is generally available, 

 inexpensive, and easy to use. The 

 concentration used in hatcheries is 

 200 p. p. m. of free chlorine. The 

 quantity of hypochlorite that has to 

 be used to obtain this concentration 

 can be calculated from the contents 

 of available free chlorine as indi- 

 cated on the product's label. Hypo- 

 chlorite in open containers and ex- 

 posed to moisture and light loses its 

 strength rapidly. 



Roccal, another widely used dis- 

 infectant, is recommended for dis- 

 infection of hands, boots, nets, and 

 other equipment. It is sold as a 10- 

 percent solution. The disinfecting 

 solution can be obtained by diluting 

 1 part of commercial roccal with 100 

 yjarts of water. Roccal is colorless, 

 odorless, and harmless, if not taken 

 internally. 



Disinfecting ponds 



Ponds can be disinfected by the 

 addition of hypochlorite, or liquid 



gaseous chlorine, to water. The 

 concentration of free chlorine 

 should not fall below 100 p. p. m. 

 during disinfection, which should 

 last at least for 1 hour. Water con- 

 taining chlorine is very toxic to fish 

 and other life. If water with chlo- 

 rine is kept in ponds for 2 or 3 days, 

 all chlorine will disappear. If, 

 however, water with chlorine must 

 be released sooner to a stream with 

 fish, the free chlorine should be 

 neutralized w i t h photographer's 

 hypo (sodium thiosulfate). Chlo- 

 rine will also kill fish parasites pres- 

 ent in water, as well as snails which 

 often act as intermediary hosts to 

 some fish parasites. 



Drying and liming of ponds are 

 also good practices; however, ponds 

 so treated must remain completely 

 dry for several months to make this 

 practice entirely effective. 



CONTROLLING PREDATORS 

 AND PESTS 



INSECTS 



Minnow ponds may become over- 

 populated with aquatic insects that 

 prey on fish fry. Of these, the bee- 

 tle larva called the water tiger and 

 the adult insect known as the back- 

 swinnner {Nofonecta) are the most 

 destructive. As both come to the 

 surface of the water for air, they can 

 be controlled by covering the ponds 

 with a film of oil. Kerosene, fish 

 oil, No. 2 fuel oil, and cod-liver oil 

 can be used for this purpose, as they 

 are not injurious to fish. The cod- 

 liver oil must be mixed with gaso- 



62 



