Cage-based mariculture as a vector of antibiotic dissemination: Evidence from seasonal and multi-compartment surveillance in a coastal mariculture bay.

Intensive cage mariculture is an important source of antibiotic contamination in semi-enclosed coastal bays. This year-round study quantified 47 antibiotics in seawater, sediments, and cultured Larimichthys crocea tissues in Ningde Sansha Bay, China, to characterize aquaculture-associated antibiotic contamination and potential ecological risks. Antibiotics were ubiquitously detected across all environmental compartments. Total aqueous antibiotic concentrations were substantially higher in December (up to 465.42 ng/L) than in May (up to 109.14 ng/L), with seasonal shifts in dominant antibiotic classes from sulfonamides/quinolones to quinolones/tetracyclines. Sediments exhibited greater antibiotic accumulation than overlying waters; in December, they showed higher antibiotic diversity and total concentrations, ranging from 21.56 to 930.27 ng/g, with quinolones consistently dominating sediment profiles. Cage aquaculture areas represented localized contamination hotspots, in which total antibiotic concentrations in cage-adjacent surface waters peaked in October at 1033.71 ng/L. Conversely, antibiotic concentrations in sediments beneath cages reached a maximum in March at 183.16 ng/g, where quinolones predominated. For cultured fish, bioaccumulation was tissue- and stage-specific. Liver burdens during the fry-rearing stage ranged from 7.43 to 636.79 ng/g, significantly exceeding those in muscle levels (p < 0.05). Muscle quinolone concentrations peaked at 294.97 ng/g, yielding a maximum log BCF of 4.52. These findings quantitatively demonstrate the significant influence of intensive cage aquaculture on the localized multi-compartment distribution of antibiotics. Although direct human health risks are limited, substantial bioaccumulation in edible tissues highlights a critical pathway for the propagation of antimicrobial resistance through the food web, warranting targeted mitigation through rational antibiotic administration.