Immersion Staining of Postlarval Shrimp 

 Ray S. Wheeler 



The purpose of this preliminary inn^mersion staining study was to 

 find a nontoxic substance that would stain postlarval shrimp vividly enough 

 to render them easily detectable with the unaided eye and would persist for 

 an extended period. Postlarval shrimp are so small that neither tagging nor 

 injection of biological stains is feasible. 



Eleven stains have been screened as possible larval shrimp stains. 

 These include six liquid food colors (Brand A green, red, blue, and yellow; 

 Brand B red and green), an Easter egg dye, and four biological stains (neu- 

 tral red medium, Bismarck brown Y, Nile blue A, and neutral red). 



The postlarval shrimp used in this study measured 10 t 1 mm. 

 They were held in recirculating sea-water tanks or aquaria until they had be- 

 come adjusted to these conditions, after which they were immersed in the 

 various stains. During the testing period, the animals were not fed. 



The effectiveness of the stains was observed at varying time inter- 

 vals of 1, 3, 5, and 10 minutes with different stain concentrations. Two indi- 

 viduals were stained simultaneously in each combination and afterward placed 

 in separate petri dishes. The results of each experiment were observed for 

 7 days. Control animals were handled in the same manner, except that no 

 stain was added. Liquid food colors were used at concentrations of 100, 50, 

 25, and 12^ percent of the commercial stock solution. Sea water was used in 

 making dilutions. Solutions made from dry biological stains, and the Easter 

 egg dye varied from 333:1 to 1,280,000:1 by weight. 



Stains were found to differ in persistency, intensity, and toxicity. 

 The uptake of stain varied between individuals even though they were stained 

 simultaneously in the same container. 



Liquid food colors (Brand A) were found to be nontoxic at 100 per- 

 cent concentration for the maximum time interval of 10 minutes. Shrimp 

 stained with the red, blue, and green colors appeared quite brilliant at the 

 higher concentrations, although color intensity diminished at the lower con- 

 centrations and shorter immersion intervals. Even at the lower concentra- 

 tions, stained shrimp were easily distinguished when released among a group 

 of unstained shrimp. Color was concentrated in the digestive tract with only 

 little staining noted in the thoracic or abdominal tissue. Of the three colors, 

 red seemed initially to be the most conspicuous and stood out with the great- 

 est brilliance. Although each of these colors faded toward the end of the 7- 

 day test period, fading was most noticed in the brilliant red coloration, which 

 became pinkish red. This faded shade of red could be confused with the nat- 

 ural red pigmentation that occurs near the base of the appendages of some 

 small shrimp. 



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