controlled experiment (table 4), total mortality 

 of injected shrimp was 6 percent less than that 

 of the controls. 



If a blue marking agent is desired, the 

 choice is about equally divided between Trypan 

 Blue and Niagara Sky Blue 6B. Trypan Blue ap- 

 pears to cause slightly less mortality, but 

 abdominal coloring associated with Niagara 

 Sky Blue 6B is retained for several weeks and 

 m.ight prove an asset in short-term marking 

 programs. 



Injection with Trypan Red, National 

 Aniline or Harleco, results in distinctive red 

 branchial coloring which has remained fast for 

 245 days and through at least two ecdyses. In- 

 jection usually results in an immediate general 

 pink coloration which is followed by branchial 

 concentration within 24 hours and subsequent 

 variable abdominal fading. 



A 1 -percent solution prepared with one 

 part of distilled water and nine parts of sea 

 water has proved most satisfactory. Glycerine 

 was used in one experiment in place of the dis- 

 tilled water, but this offered no advantage. 

 Overinjection causes a high mortality which may 

 continue for several days, and losses of equil- 

 ibrium occurring more than a month after 

 staining can probably be attributed to excessive 

 injections. Individual injections should cease 

 as soon as a general pink coloration is observed, 

 and should not exceed a volume of 0.03 cc. with 

 medium shrimp. 



With the exception of deaths attributed 

 to overinjection, total mortalities have been 

 low considering the long holding periods . There 

 is Uttle doubt that some deaths have resulted 

 from the suspected environmental deficiency as 

 previously noted. 



A number of stains tested by the feeding 

 technique produced various degrees of tempor- 

 ary abnormal coloration, but only Trypan Red 

 caused lasting and distinct coloring suitable for 

 field identification. Feedings stained with Try- 

 pan Red resulted in a bright-red branchial color 

 which remained fast for more than 233 days and 

 throu^ a minimum of three ecdyses. Marking 

 was successful in all sizes of shrimp from 30 

 mm. through 175 mm. 



Excessive feeding, indicated by various 

 degrees of pink to red general staining, results 

 in high mortality with deaths frequently preceded 

 by loss of equilibrium . With controlled staining, 

 however, mortality compares favorably with 

 that of normal shrimp. Staining of individual 

 shrimp usually accomplished in one or two feed- 

 ings over a like number of days. Since aggres- 

 siveness and appetite vary with the individual, 

 it is impossible to stain a group of shrimp simply 

 on the basis of a predetermined number of stained 

 feedings. Before each stained feeding, shrimp 

 should be examined for the presence of the char- 

 acteristic bright -red branchiae, and individuals 

 so colored should receive no further stained 

 food. With a minimum of experience it is soon 

 possible to separate properly marked shrimp 

 with facility. 



Staining is equally pronounced with solu- 

 tion concentrations of 1 percent and 2 percent, 

 but the 1 -percent solution is favored as a further 

 check against over staining. Since no advantage 

 was found in using sea -water solutions, distilled 

 water is the preferred solvent. Although differ- 

 ences were inconsistent, the Harleco stain ap- 

 peared to produce a slightly brighter color than 

 the National Aniline product. 



All of the so-called fast stains described 

 above exhibit a slight tendency to fade, but in 

 every case the remaining color is quite distinct 

 over the period indicated. Whether stained 

 shrimp will retain abnormal coloration over 

 similar periods under natural conditions cannot 

 be ascertained without field testing. 



Under the conditions of the experiments, 

 captive shrimp did not exhibit normal growth . 

 Stained and normal shrimp held for extended 

 periods showed little observable size increment 

 even after several shedding cycles . Under con- 

 ditions of normal growth, it is doubtful whether 

 a 30- or 40-mm. shrimp could retain sufficient 

 stain to enable identification as an adult. 



Despite these questionable factors, the 

 use of the recommended stains and procedures 

 offers a new and useful tool for shrimp fishery 

 investigations. Marking by injection is a rapid 

 method applicable to either sea or shore -based 

 operations. The feeding technique, though 

 probably restricted to use at shore stations, 



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