Because eggs are tender during the early stages of development and 

 require extremely careful manipulation^ it is highly desirable that 

 disinfection with sulfo-merthiolate be effected either verj' soon after 

 the eggs are water-hardsned or after they are eyed. Eggs not in the 

 tender stage can be disinfected in several vays: (1) they can be poured 

 into a pan or tub mth a solution of sulfo-merthiolate and stirred virith 

 a feather or by hand during disinfection. After disinfection, they 

 should be drained and placed in fresh water. (2) Eggs can be 

 distributed in hatching trays and then immersed with the trays in the 

 disinfectant. After disinfection, they can be placed in the hatching 

 troughs ;vithout rinsing (Snieszko and Friddle 1943). 



According to Gee and Sarles (194-2) sulfo-merthiolate in dilution 

 of 1:7500 kills B. salmonicida in the presence of trout eggs within 10 

 minutes. As this drug is not toxic to trout eggs even in much lower 

 dilutions, 1:5000 dilution gives better assurance of thorough 

 disinfection. In wiiichever manner eggs are disinfected, they should be 

 exposed to the action of the disinfectant for no less than 10 minutes. 

 During that time eggs, except in the sensitive stage, should be moved 

 at least once every 2 minutes to expose all surfaces to the disinfectant 

 (Sniesako and Friddle 194S). 



As many as 50,000 eggs can be disinfected in 10 liters of 

 disinfectant solution. Several small batches of eggs can be treated in 

 the same batch of sulfo-merthiolate, providing that the solution is well 

 aerated and not more than a few days old. Sulfo-merthiolate does not 

 attack metal, but because even traces of zinc are toxic to fish, it is 

 safer to dip eggs in a painted enamelled or glass vessel. This drug 

 should never be exposed to direct sunlight (Snieszko and Friddle 1948). 



Regardless of the disinfectant used, all damaged, clouded, and 

 spotted eggs should be discarded and destroyed as B. salmonicida or 

 other pathogenic bacteria may be within the eggs, and these organisms 

 might not be reached and destroyed (Snieszko and Friddle 1948). 



Care of Fish- Immunization and Selective Breeders 



Besides the construction of hatcheries designed to reduce the 

 possibility of disease transmission, disease prevention requires the 

 establishment of conditions which will maintain the vitality of fish 

 (Belding 1927). 



In order to m.aintain a resistant stock of trout Belding (1927) 

 suggested the follcaving rules: 



(1) Do not crowd fish. Keep the stock below the maximum number 

 v^iich may be accommodated. 



(2) Do not overfeed. Use no raw food. 



63 



