the tissues of a brown trout possessing a blood-sulfonamide level which 

 is nonprotective^ this pathogen can remain in tissues in a state of 

 temporary arrested virulence. The state of arrested virulence can 

 continue to ejdst despite the subsequent establishment of a "protective" 

 blood-sulfonamide level. Consequently^ an active infection could 

 develop when the blood-sulfonamide level drops to a nonprotective value. 

 On the other hand^ when B. salmonicida enters the tissues of a brown 

 trout possessing a protective blood-sulfonamide levels the organism can 

 be retained in the host without producing an active infection. It was 

 observed that active infection did not develop even after the blood 

 level had dropped below the protective range (found to be below 7 mg. 

 per 100 ml. of blood). 



Satisfactory therapeutic results were obtained by Outsell and 

 Snieszko (1949a) with dosages of 8,8 and 13.4 mg, per 100 gra, of trout 

 per day (4 and 6 gm, , respectively^ of sulfamerazine per 100 pounds 

 of fish per day). Flakas (1950b) found that the therapeutically 

 effective dosage of sulfamerazine in the treatment of furunculosis in 

 adult brown trout was 17.6 mg. per 100 gm. of fish per day (8 gm, of 

 drug per 100 pounds of fish per day). After 4 days of such treatment, 

 the blood level rose to 7 mg, percent. 



Results of Snieszko and Friddle (1951) indicate that absorption 

 of those sulfonamides which are most effective in the treatment of 

 furunculosis is somewhat slower in fishes than in warm-blooded animals 

 (Litchfield 1939), In order to bring about a fast, therapeutically 

 effective blood concentration of sulfamerazine ^ trout should receive 

 during the first 3 to 4- days of treatment 20 to 30 gm. of the drug per 

 100 kilograms of fish per day (10 to 15 gm, per 100 pounds). After this 

 initial period, dosage can be reduced by 25 to 50 percent without 

 lowering the blood concentration of sulfonamides below the minimum 

 effective level. 



According to Flakas (1950b), about one-third of sulfamerazine 

 should be replaced by sulfaguanidine, Sulfaguanidine exerts its effect, 

 for the most part, in the intestinal tract and since the intestinal 

 tract of trout carries B, salmonicida during active infection, this 

 affords a good source of infection by which the disease may be spread. 

 Flakas (1950b) felt that sulfamerazine alone was not totally effective 

 as a means of ridding a trout hatchery of B. salmonicida . 



Outsell and Snieszko (1949a) and Snieszko and Friddle (1951) 

 outlined the following general recommendations for sulfonamide treatment 

 of ifurunculosis., and possibly other infectious diseases of fishes: 



1. Treatment should be started as early as possible, because 

 fish in the advanced stage of the disease cannot be saved, 



2. Bacteriological examination of diseased fish should be 

 carried out as soon as possible. Other diseases, which in their 



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