Comparison of water quality, planktonic community, and volatile organic compounds in the seawater from five cage culture areas of large yellow croaker

Abstract

The rapid development of marine fish cage farming has led to ecological damage, adversely affecting fish quality. Significant regional quality differences in large yellow croaker under similar farming conditions suggest that the water environment plays a crucial role in fish quality. Using full-length18s/16 s rRNA sequencing with bacterial absolute quantity and headspace solid-phase microextraction coupled with gas chromatography mass spectrometry (HS-SPME-GC–MS), we investigated the planktonic community and volatile organic compounds (VOCs) in seawater from cages housing large yellow croaker at five major mariculture sites in China, including ND (26.627°E, 119.638°N), NJ (27.479°E, 121.052°N), DT (27.981°E, 121.196°N), NC (28.470°E, 121.907°N), and DJ (30.198°E, 122.698°N). Notably, three dominant ciliates, Mesodinium rubrum, Strombidium sp., and Pseudotontonia simplicidens, were identified in NJ as bioindicators for water quality. Additionally, NJ cages had the highest bacterial biomass with 54 % Synechococcus CC9902, and the lowest abundance of bacteria with pathogenic activities. These may explain NJ's optimal water quality parameters and the highest eukaryotic biodiversity. In contrast, DT and DC contained only the core ciliate M. rubrum, with no dominant ciliate in ND. Styela gibbsii, a filter feeder, predominated in ND cages, adhering to the net. The occurrence of red tide-causing species and pathogenic bacteria or fungi was notable in DJ, DC, DT, and ND, including Akashiwo sanguinea, an unclassified Dinophyceae, Gyrodinium fusiforme, Pirum gemmate, Candida parapsilosis, Hortaea werneckii, and Pseudomonas juntendi. Bacterial functional analysis showed that ND cages harbored unique strains linked to ureolysis and various pathogenic activities. Co-association networks suggested that 2,4-Di-tert-butylphenol and pentadecane might play roles in communication within plankton communities. A rise in pleasant VOCs such as acetyl valeryl, pentadecane, butyl butyrate, tetradecane, and 5-butyldihydro-2(3H)-furanone was observed in DJ, DC, DT, and NJ, compared to ND. The results provide valuable insights for improving aquaculture practices and mitigating environmental impacts. The results provide valuable bioindicators for monitoring water quality using microbial communities and VOC profiles.