Passage efficiency and fish behavior of Laokou navigation junction fishway using passive integrated transponder (PIT) telemetry

Passive integrated transponder (PIT) radiofrequency (RF) chip tracking has been widely used to monitor the fish migration movement, and then quantify fish passage efficiency. The present study aims to determine the fish passage efficiency and the behavior at the Laokou transportation hub of the Yujiang River. The test site of passage was selected as the total length of 718 m, where the design slope of the pool chamber was 1:60. The upstream and downstream water levels varied from 75.46 to 75.53 m, and 67.00 to 67.07 m, respectively, in the test period. The exit and entrance depths of the fishway were 1.8 and 3.1 m, respectively. The dominant specie of Cirrhinus molitorella was used as the test object. The full length of the test fish ranged from 16.00 to 23.50 cm, with a mean value of (19.05±1.49 cm). Half-duplex (HDX) PIT-tagged RF chip tracking system was constructed with the dorsal muscle implantation of PIT tags in the test fish. The behavior of tagged fish was then characterized in five monitoring sections of the fish passage. A quantitative evaluation of passage efficiency was carried out on the fish passage. The flow velocity and water temperature were measured to determine the dissolved oxygen and pH during monitoring. A total of 1 136 signals were collected from the five antennas. The results showed that the tagged test fish passed through the fish passage for an experienced duration of 648 to 5 359 min with a total passage efficiency of 50.79%. According to the ANOVA, there was no significant difference (P>0.05) in the total length of fish passing in the five sections. In addition, specific patterns were found in the fish behavior; The test fish was more active in the fishway at all times during the day (06:00 to 18:00), while at night (18:00 to 06:00) no detection was recorded for 7 h. Furthermore, 80.95% of the individuals rapidly passed up or swam out of the fishway through the monitoring cross-sections, whereas, 19.05% of the individuals experienced a stopover when passing. Passage speeds varied considerably between the two transects, with the slowest speed (0.75±0.32 m/min) through the first transect. Eight fish showed a downward movement in this test. Therefore, the test fish was the most active from 05:00 to 09:00, while there was basically no detection signal at night, indicating that the test fish was in a resting condition at night. There was a basically reasonable flow rate and the residence time of fish passing through the section at Laokou. The duration of passing fish was more than 10 h, most of which was to swim from release to the first section. The slow flow velocity was the important influencing factor in the downstream section of the fish passage. Subsequent experiments also need to enrich the test fish species and number, in order to supplement the fish passage entrance on the entry efficiency. This finding can provide a strong reference to quantify the fish passage efficiency and behavior in crossing facilities.