Comparisons of P. setiferus fed the artificial diet with those fed 

 a variety of natural foods (liver, shrimp, oatmeal, and wheat germ) indicated 

 that the animals fed artificial food had only a slightly increased laboratory 

 life span. Of more significance was the decrease in frequency of the patho- 

 logical condition shown in the figures. Fifty percent of the animals fed nat- 

 ural foods developed these dark, blistered areas on the ventral portion o^ 

 the carapace; less than half as many cinimals fed the artificial food showed 

 the change. Microscopic examination of this lesion showed it to be between 

 the layers of the carapace itself--a dark fluid-filled blister which did not 

 harden after the completion of the molt. Animals usually died within 24 hours 

 after the development of the blister. The lesion was found in both P. setiferus 

 and P. aztecus, but it occurred with less frequency in P. aztecus. 



White and brown shrimp showing a dark blister on the ventral area of the 



carapace. 



47 



