Abstract.A device for self‐separating newly metamorphosed post‐larvae prawns from larval culture tanks was designed based on the rheotactic activity exhibited by freshwater prawns after metamorphosis into post‐larvae. The performance and effectiveness of the post‐larvae selector were evaluated under (a) 24‐h periods, (b) four water flows and (c) at two tank depths. A high migratory response (90 confidence level) during the dark period with a water flow range of approximately 11 pm was found. Thus the device has shown to be highly efficient in separating post‐larvae in mixed population tanks. The avoidance of excessive handling stress, and the continuous automatic removal of post‐larvae immediately following metamorphosis into juveniles are two of the most important advantages of this design as compared to other separ
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