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Abstract
The study used Holt's method (1963) to determine the selectivity for the length of chinese gizzard shad (Clupanodon thrissa) caught by 5 gillnet samples with different mesh sizes: 45, 50, 55, 60 and 65 mm. 120 trial batches were collected with a total of 1,789 samples of chinese gizzard shad from November 2021 to October 2022 in the coastal waters of Nghi Loc district and Cua Lo town, Nghe An province. The results showed that the optimum total length of captured chinese gizzard was 135.4; 150.4; 165.5; 180.5; 195.5 mm and the optimal fork length is 112.9; 125.5; 138.0; 150.6; 163.1 mm with mesh sizes of 45, 50, 55, 60 and 65 mm, respectively. The overall selectivity coefficient for total length was 3.0 and fork length was 2.5. The minimum mesh size from 67 mm is considered suitable for catching chinese gizzard shad with a total length of 200 mm in the studied waters.