This research aims to determine the best currents speed and utilization of venturi to increasing survival, growth of Cyprinus carpio L. and reducing the infection rate of A. hydrophila bacteria. fingerlings. This research used an experimental method completely randomized design (CRD) with four treatments and four replications. The treatments used were the use of currents and venturi on the maintenance media with currents velocities of 0 m/s (A), 0.06 m/s (B), 0.1 m/s (C), and 0.14 m/s (D). Maintenance of the test fish for 40 days then followed by a challenge test for 14 days. Koi fish fingerlings tested to use A. hydrophila with a density of 108 CF /ml. The parameters observed included white blood cells, red blood cells, clinical symptoms, survival, daily growth rate, feed conversion ratio and water quality. The results showed that the use of currents and venturi with a flow rate of 0.14 m/s was effective in improving the performance of the koi fish’s immune system and reducing the infection rate of A. hydrophila bacteria. During the flow administration during the 40 days maintenance period, the white blood cell count increased by 20.51% from a value of 9.19 × 104 cells/mm3 to 11.56 × 104 cells/mm3. Red blood cells increased by 40.65% from 1.60 × 106 cells/mm3 to 2.69 × 106 cells/mm3. Currents treatment with a speed of 0.14 m/s produced the highest survival rate after challenged with a value of 86.7%. Also this treatment was effective in preventing infection of A. hydrophila bacteria, it can be seen from the macroscopic clinical symptoms that appear less than the treatment current. The best results of daily growth rate and feed conversion ratio provided in currents treatment with a speed 0.1 m/s.
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