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Abstract
The giant freshwater prawn, Macrobrachium rosenbergii, was assessed as a migratory aquatic species directly affected by Phuoc Hoa dam on Be river. The purpose of this study was to propose a suitable operation regime of water velocity for M. rosenbergii to migrate on Phuoc Hoa fish-passage. The research contents included: (1) Surveying the current conditions of the water velocity operation and design parameters of the fish-passage; (2) Monitoring the prawn ratio and speed of passing through an open-flume at water velocities; (3) Observing the prawn ratio of maintaining at the head of the flume at water velocities for extended periods of time. The study was conducted on the two prawn's sizes of 7.5-9.5 cm (Prawn size I) and 13.5-15.5 cm (Prawn size II), with an 18 m long flume creating water velocities in hydraulic laboratory. The results recorded that the average water velocities in the dry and rainy seasons and the maximum water velocity in the rainy season in Phuoc Hoa fish-passage were 0.26, 0.59 and 0.90 m/s respectively, as a basis for three levels of water velocity arrangements (0.3, 0.6 and 0.9 m/s) under experimental conditions. The monitoring results showed that the prawn ratio of moving through the 18 m flume for 10, 20 and 30 minutes at the water velocity of 0.3 m/s was 13.33, 68.33, 94.17% for Prawn size I; and 21.66, 76.00, 98.33% for Prawn size II respectively; at the water velocity of 0.6 m/s was 2.50, 50.83, 79.16% for Prawn size I; and 9.16, 61.66, 90.83% for Prawn size II respectively; at the water velocity of 0.9 m/s, the prawn ratio of moving through the 18 m channel was 0%. The prawn speed of moving through the 18 m channel at the water velocities of 0.3 and 0.6 m/s was 1.15 and 0.92 m/min for Prawn size I; 1.18 and 0.96 m/min for Prawn size II respectively, showing that Prawn sizes I and II need at least 11.81 and 11.51 hours at the water velocity of 0.3 m/s; 14.76 and 14.15 hours at the water velocity of 0.6 m/s to move between the farthest resting pools on the fish-passage. The prawn ratio of maintaining at the head of the flume for 5, 10 and 15 hours at the water velocity of 0.3 m/s was 88.33, 69.17, 30.83% for Prawn size I; and 91.67, 83.33, 47.50% for Prawn size II; at the water velocity of 0.6 m/s, it was 70.83, 36.67, 0% for Prawn size I; and 82.50, 48.33, 12.50% for Prawn size II respectively. The results of the study were practically linked to Phuoc Hoa fish-passage with the proposed operating regime of the surrounding water velocity of 0.6 m/s and the addition of resting pools along Phuoc Hoa fish-pass to increase the movement efficiency of M. rosenbergii through the fish-passage.
Key words: Moving performance, water velocity, the giant freshwater prawn, fish passage, Phuoc Hoa