Trophic fractionation in an integrated multi-trophic aquaculture off Tongyoung Coast: A stable isotope approach

Abstract This study investigated trophic fractionation of fish-derived waste materials by co-cultured species in an integrated multi-trophic aquaculture (IMTA) practice off Tongyoung Coast. Additionally, this study was aimed to identify suitable extractive species based on stable isotope analysis. Red sea bream (Pagrus major) was cultured along with sea cucumber (Apostichopus japonicus), suspension feeding bivalves (Crassostrea gigas and Mytilus galloprovincialis) and seaweeds (Ulva sp., Undaria pinnatifida and Sargassum fulvellum). Stable isotope ratios namely δ13C, δ15N and δ18O were determined. The δ13C, δ15N and δ18O values recorded in P. major were − 21.50 ± 0.20‰, 13.18 ± 0.17‰ and 17.52 ± 0.88‰, respectively. The δ13C, δ15N and δ18O values among the extractive species were ranged as (−19.90) – (−15.55) ‰, 6.14–10.82‰ and 15.14–23.17‰, respectively. The sea cucumber Apostichopus japonicus was directly consuming finfish waste for their food and proved to be most important extractive co-cultured species in this IMTA system. Crassostrea gigas is the second most important species followed by Mytilus galloprovincialis. Cultured seaweeds are least responsible to reduce waste loads within IMTA system. However, the lack of isotopic consistency between IMTA and control feeders suggested that least contribution of aquaculture waste into neighboring coastal environment. Therefore, Apostichopus japonicus, Crassostrea gigas and Mytilus galloprovincialis should be considered as extractive organism in commercial IMTA system to reduce the waste load in ambient environment.