The purpose of this study is to development an underwater low-frequency RFID system for management and live monitoring of broodfishes by hardware construction, software programming and some actual POC (Proof of Concept) works. Results are summarized as follows:1. Because of RFID magnetic-field characters itself, sensing distance will reach the longest range while paralleling the reader antenna magnetic line of force and tag coil. In other word, put the directions of long-axis of tag and plane of reader antenna vertically as possible.2. The best choice RFID tag, considering for underwater and large sensing area, are products from TI (Taxes Instrument Co. Std.). With new design of 4 types of RFID reader antenna, the successful reading rate will be up to 97% in maximum reading distances (50cm in water, 39cm in air).3. After integrated the low-frequency anti-collision RFID reader SDK, related designed adaptive device and 20cm square antenna, 10 RFID tags can be identified in the same time (within 1 second).4. Advantages of injecting RFID tags are high sensing rate, low fall-off rate and low damage to fish, but harder for operating. In the other hand, mounting RFID tags are easier to use but easier to fall off in a high density culture pool and fish-body collisions situation.5. Whatever injecting or mounting RFID tags on fishes, the readable coverage will be good than 90% in an actually case for constructing 12 underwater 60cm*80cm antennas in a 3m-diameter, 1m-depth FRP aquacultural tank. Basically, cultural ecology and moving character of broodfishes can be observed and analyzed successfully.