Effects of fish-shellfish-algae polyculture on growth of large yellow croaker (Larimichthys crocea) and water quality regulation

Filter-feeding shellfish and macroalgae play a significant role in food production and ecological regulation within integrated multi-trophic aquaculture (IMTA) system. To investigate the effects of polyculture of oysters (Crassostrea rivularis) and macroalgae (Gracilaria verrucosa) on the aquaculture performance of large yellow croaker (Larimichthys crocea), we compared the impacts of monoculture (Fish-only) and different IMTA modes (Fish-shellfish, fish-algae, and fish-shellfish-algae polyculture) on the water quality and growth of L. crocea. The results show that IMTA model significantly improved water quality and promoted the growth of L. crocea. The contents of ammonia nitrogen ( ${\mathrm{N}\mathrm{H}}_4^{+}\text{-N}$), nitrate nitrogen ( ${\mathrm{N}\mathrm{O}}_3^{-}\text{-N}$), nitrous nitrogen ( ${\mathrm{N}\mathrm{O}}_2^{-}\text{-N}$) and active phosphate ( ${\mathrm{P}\mathrm{O}}_4^{3-}\text{-P}$) in the fish monoculture system increased significantly along with time, while the IMTA systems (Especially the fish-shellfish-algae polyculture) reduced the accumulation of nutrients in the water through the synergistic effect of oysters and Gracilaria. Among them, the contents of ${\mathrm{N}\mathrm{H}}_4^{+}\text{-N}$ and ${\mathrm{N}\mathrm{O}}_3^{-}\text{-N}$ at the mid-to-late culture stages of fish-shellfish-algae (LOC212 group) were (1.94±0.11) and (2.83±0.28) mg·L⁻¹, compared with the monoculture systems [(3.40±0.31), (6.51±0.98) mg·L⁻¹] were significantly reduced by 42.76% and 56.49% (p<0.05). Additionally, the dissolved oxygen and water transparency in IMTA system were significantly higher than those in the monoculture systems during the mid-to-late culture stages. In terms of growth performance, the survival rate [(98.33±2.89)%] and body mass gain rate [(5.91±3.31)%] of L. crocea in fish-shellfish-algae polyculture were significantly higher than those in monoculture group (p<0.05), indicating that the synergistic effect of fish-shellfish-algae was more conducive to the growth of L. crocea. In conclusion, the IMTA model achieves the dual goals of water quality regulation and growth optimization through the synergistic effect of multiple trophic levels, providing an ecologically efficient aquaculture strategy for L. crocea in southern regions.