28 tr. S. BUREAU OF FISHERIES. 



fish, brine, salt piles, and fish agar saturated with salt. No growth 

 appears on media containing less than 15 per cent salt, by weight. 

 Due to their sensitiveness to changes in density, staining of these bac- 

 teria for microscopical examination is very difficult. The morphol- 

 ogy or shape of the organisms depends upon the concentration of salt 

 in the medium, varying from the largest form (14-16 micra), found 

 in heavily saturated media, to the spherical form (2 micra diameter) 

 in media of 16 per cent concentration. Likewise all intermediate 

 forms are present in the concentrations between 15 per cent and sat- 

 uration. The amount, character, and pigmentation of the colonial 

 does not seem to be affected by the varying changes in the concen- 

 tration of salt. 



The most favorable temperature for the growth of both the spiro- 

 chete and the bacillus is between 50 and 60° C., indicating the salt 

 lagoons of the Tropics as the probable source of the infection. Sun- 

 light is not germicidal to these organisms, and this also points to 

 their tropical origin, where the pigmentation is required as a pro- 

 tection against the bright sunlight; ordinary bacteria are killed by 

 10 minutes' exposure to bright sunlight. Influenced by age, by the 

 accumulation of their own metabolic products, and particularly by 

 low temperatures, both organisms suffer a temporary loss of pigmen- 

 tation. During this loss the formation of the so-called " coccoid 

 bodies " is noted in the pink spirochete. No change in the shape of 

 the bacillus during the absence of pigment has been noted. After 

 transplantation, both pigmentation and the regular vegetative form 

 is resumed. 



All results indicate that the causative agents of this troublesome 

 and costly coloration have been discovered and that their original 

 source is the solar evaporated sea salt in which the fish are cured. 

 Both European and American sea salts are infected. Mined or do- 

 mestic salt seems to be free of their presence. Any method devised 

 for the elimination of this reddening of salted fish must be based 

 upon either the proper disinfection of the sea salt before use or the 

 substitution of mined or domestic salt which is free of infection. In 

 either case a thorough disinfection of the salt fish plants and equip- 

 ment is essential, since at the present time all are highly infected. 

 It would be useless to dump sterilized salt or even mined salt into a 

 highly infected plant or to bring unsterilized salt into a thoroughly 

 disinfected plant. 



With this knowledge of the life history of the organisms, the con- 

 ditions essential for their growth, and the sources of infection, the 

 Bureau already has under way experiments to determine the best 

 and most practical means of eradicating a most troublesome factor 

 from the salt-fish industry. During the entire series of experiments 

 the Bureau has had the hearty cooperation of the salt-fish industries. 



LOCATION OF FISH FROM AIRCRAFT. 



In July, 1919, in cooperation with the Naval Aviation Service, 

 W. W. Welsh, a scientific assistant in this Bureau with naval experi- 

 ence, made a flight at Cape May, N. J., to determine the possibilities 

 of scouting for schooling fish with the aid of aircraft. The results 

 of this trial were very favorable, but, since the development of the 

 method and its application to the fisheries lies properly within the 



