A preliminary study on monitoring of stock-enhanced and released fish in Wuzhizhou Island based on environmental DNA (eDNA) metabarcoding

Fish stock enhancement release is one of the core methods in the construction of marine ranches. The environmental DNA (eDNA) metabarcoding technology has advantages such as convenient sampling and accurate species identification. Moreover, it can well reflect the species biodiversity of fish and has a good correlation with the relative biomass of fish. Exploring the dispersion pattern of eDNA from the enhanced fish in the release area can facilitate the future use of eDNA technology to assess the effectiveness of fish stock enhancement releases. We conducted an experiment at Sanya Wuzhizhou Island Marine Ranch, having collected the water samples one day before (D1) and 1 (D2), 4 (D3), 7 (D4), 16 (D5) and 45 (D6) days after the fish stock enhancement. We applied eDNA metabarcoding technology to track the diffusion dynamics of Lutjanus sebae, L. erythropterus, and Epinephelus coioides. The results show that no enhanced fish were detected before the release, and L. sebae was only detected in water collected at IN2 site in the core area on D3, while the other two species were not detected at any time or site. There was no significant difference in the fish community structure obtained on D2 and D3 after the stock enhancement compared with D1 (p>0.05, r<0.08), while the fish community structure on D4, D5 and D6 differed significantly from that on D1 (p<0.05, r>0.7). The study indicates that the low detection rate of stock-enhanced fish in the area and the poor effect of stock enhancement may be related to the lack of domestication of the fish or the influence of environmental factors on the eDNA concentration of the released fish.