A Device for Measuring Live Shrimp 



Donald M. Allen 



Growth studies of shrimp using the nnark -re capture method require 

 a rapid and accurate method of measuring large numbers of the living animals, 

 Previous experience using vernier calipers to measure carapace length and 

 conventional fish-measuring boards to measure total length showed these 

 methods to be unsuitable. The grip required to secure a live shrimp for meas- 

 urement may injure the animal, and the time involved is prohibitive. These 

 problems are magnified when dealing with very small shrimp, which are both 

 agile and fragile. 



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DOWL PLUG TOP VIEW 



Shrimp measuring de- 

 FRONT VIEW vice made of plastic 



tubing. 



A simple device to measure live shrimp w^ith none of the above dis- 

 advantages was developed. The device, essentially a calibrated trough with 

 a handle, is constructed of clear plastic tubing having a 1/8-inch wall. The 

 length and diameter of the tubing are- determined by the sizes of the shrimp to 

 be measured. For shrimp ranging from about 60 to 140 mnn. total length, an 

 1 1 -inch length of 3/4-inch tubing is used. Five inches of tubing is retained as 

 a handle. The trough is formed by removing, lengthwise, one-half of the re- 

 maining 6 -inch section of the tube. A short, slightly tapered plastic dowel is 

 forced into the tube where it joins the trough and cemented. The exposed end 

 of the secured dowel forms a base line for calibration and measuring purposes. 

 To determine absolute total lengths, a strip of millimeter paper, appropriately 

 numbered, is taped to the convex surface of the transparent trough where it 

 can be easily read but not become worn. To rapidly separate large numbers 

 of shrimp into preselected size groups, variously colored strips of plastic 

 tape, each representing a narrow size range, are affixed to the trough at 

 appropriate distances from the base line. 



In use, the device is held by the handle in one hand. A shrimp is 

 laid in the trough with the tip of the rostrum touching the exposed dowel end. 

 The trough restricts movement and holds the shrimp in an extended position 

 so that an accurate total -length measurement can be made with a minimum 

 of handling or pressure. Using this device, several hundred live shrimp can 

 be measured per hour with practically no mortality. 



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