Yellow food coloring (Brand A) was light in color, lacking the con- 

 trast necessary to make it readily distinguishable. For this reason it was 

 regarded as unsuitable. 



Shrimp stained with green food color (Brand B) showed good color- 

 ation of the gastric mill and gut. Immediately after staining, signs of distress 

 were noted and heavy mortality occurred overnight. This stain was therefore 

 regarded as unsatisfactory. 



Red food color of Brand B demonstrated the same qualities as those 

 of Brand A. 



At concentrations of 1,000:1 by weight, the Easter egg dye was 

 neither toxic nor did it stain. 



Neutral red medium at the lower concentrations failed to stain and 

 at the higher concentrations proved to be toxic. 



The color imparted by Nile blue A, although faint at the higher con- 

 centrations, showed promise in that it was not toxic. The color within the ab- 

 dominal tissue persisted throughout the observation period. 



Neutral red was not toxic and demonstrated good staining qualities 

 at the higher concentrations and longer time intervals. The digestive tract 

 was colored a dark red and the abdominal tissue a lighter red. This color 

 persisted throughout the observation period. 



Bismarck brown Y was not intense enough nor was there enough 

 contrast to make it easily detectable. Mortality was low. 



In addition to the standard tests, two groups of postlarvae were 

 stained and held for 2 weeks in 15 -gallon aquaria. The aquaria bottoms were 

 covered with sand, and Mysidacea were introduced as food. Group 1 was 

 stained with Brand B red food color, while neutral red was used in group 2. 



Although mortality was low, the intensity of the stain in group 1 

 diminished each successive day until on the 3d day many of the shrimp had 

 lost their color entirely. On the 4th day, we examined each individual and 

 found that only 7 of the 50 originally stained had retained enough color to 

 make them easily distinguishable with the unaided eye. Twenty -three others 

 bore enough stain to be distinguishable under the binocular microscope. Sev- 

 eral digestive tracts contained sand, suggesting that the dye had been elim- 

 inated in the feces. 



In group 2, some color had faded, but enough color was retained 

 in the digestive tract and abdominal tissue at the end of the 2d week to nnake 

 it distinguishable with the unaided eye. 



As previously indicated, the work presented here is preliminary. 

 Indications are, however, that additional work will yield a suitable stain. 



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