Quinolone antibiotics (QNs) contamination in the aquatic environment is a global public health issue considering their resistance and mobility. In this study, a simple, efficient, and sensitive method was developed for the accurate quantification of fifteen QNs in water using automated disk-based solid-phase extraction (SPE) coupled with ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS). By utilizing a 3M SDB-XC disk to enrich QNs from a 1000 mL water sample, the detection limits were improved to 0.008–0.055 ng/L due to the satisfactory enrichment factors of 897−1136, but only requiring about 60 min per six samples. The linearity of the method ranged from 0.05 to 100 μg/L for the 15 QNs, with correlation coefficients of 0.9992–0.9999, and the recoveries were in the range of 81–114%, with relative standard deviations of 0.2–13.3% (n = 6). The developed method was applicable for the quantification of trace QNs at low ng/L levels in drinking and environmental waters. The results showed that no QNs were detected in tap water, while three and four QNs were detected in the river water of Zhoushan and the seawater of Daiquyang and Yueqing Bay, East China, respectively, with a total concentration of 1.600–8.511 ng/L and 1.651–16.421 ng/L, respectively. Among the detected QNs, ofloxacin (OFL) was the predominant compound in river water, while enrofloxacin (ENR) was predominant in seawater. The risk quotient (RQ) results revealed that QNs posed a low risk to crustaceans and fish, but a low-to-medium risk to algae, and OFL presented the main ecological risk factor in river water, while ENR and CIP in seawater. Overall, the proposed automated disk-based SPE–UPLC–MS/MS method is highly efficient and sensitive, making it suitable for routine analysis of QNs in drinking and environmental waters.

This study investigated the monthly variations of bacterial communities in the surface seawater of the Wenzhou coastal area and their influencing factors, while exploring the ecological functions of microbial communities. The results indicated that the surface seawater bacterial communities in this region exhibited high diversity, with significantly higher diversity observed in the winter half-year compared to the summer half-year. The bacterial community structures showed distinct monthly variations, with high similarity between adjacent months, particularly from June to September. The dominant bacterial taxa primarily included Proteobacteria represented by the SAR86 clade, OM43 clade, and Rhodobacteraceae; Bacteroidota represented by Flavobacteriaceae; and Cyanobacteria mainly composed of Cyanobium PCC-6307 and Synechococcus CC9902. Temperature and nitrate ions were identified as the environmental factors most strongly correlated with monthly bacterial community variations, while dissolved oxygen, nitrite ions, and total organic carbon also showed significant correlations with relative abundances of certain taxa. Predictions of the bacterial community’s ecological functions revealed that chemoheterotrophic functions were most abundant throughout the year, whereas photoautotrophic functions were primarily enriched in summer. Denitrification and other nitrogen cycling-related functions also displayed obvious monthly variations. Collectively, this study provides valuable insights into the temporal changes in coastal microbial communities and their interactions with different environments.

While the detrimental effects of high temperature stress on fish growth and disease resistance have been widely reported, its impact on muscle quality has received limited attention. In this study, largemouth bass Micropterus salmoides with an initial body weight of 45.73 g were subjected to a 60-day growth trial (~25 °C), followed by a 5-day acute warming phase and a subsequent 30-day chronic high temperature exposure (32 °C). Through integrated analyses of morphological parameters, texture characteristics, TUNEL assay, gene expression analysis, and metabolomics in muscle, the effects of high temperature stress on the meat quality of largemouth bass were systematically examined. The results showed that high temperature stress significantly upregulated key genes in the ubiquitin-proteasome pathway (trim13, foxo1α) and key genes in the autophagy-lysosome pathways (lc3α, lc3β, bcl2l1, ctsl2), induced apoptosis in muscle cells, and led to significant reductions in myofiber diameter and density. In terms of textural properties, high temperature stress significantly decreased parameters such as springiness, adhesiveness, and cohesiveness, as well as water holding capacity. Metabolomic analysis further revealed that high temperature induced remodeling of energy metabolism and significant reprogramming of purine and amino acid metabolic pathways, resulting in decreased levels of key flavor compounds, including IMP, GMP, flavor amino acids (glutamic acid, alanine, methionine, arginine, proline), and peptides (glu-glu-lys and glu-cys-gly), thereby adversely affecting muscle flavor quality. The findings of this study provide a theoretical basis for understanding the impact of thermal stress on the eating quality of farmed fish.

The replacement of fishmeal (FM) in aquafeeds for carnivorous fish remains challenging due to reduced palatability and adverse effects on liver health and intestinal microbiota. Marine by-products-based additives containing fish protein hydrolysates and seaweed polysaccharides have shown potential to overcome these limitations. This study evaluated the effects of graded supplementation of Haiweisu (HWS), a multi-marine by-product formulated with squid viscera hydrolysate, small-molecule components from fish protein hydrolysate, seaweed polysaccharides, and seaweed residue as a carrier, in a FM-free diet for juvenile largemouth bass. Four isonitrogenous and isolipidic diets were prepared: a FM-free control diet (CON) and three diets supplemented with 10, 20, or 30 g/kg HWS (designated S10, S20, and S30, respectively). Each diet was fed to triplicate groups of fish (29.26 ± 2.61 g) for 56 days. Results showed that HWS supplementation linearly increased final body weight, weight gain rate, and feed intake, while significantly reducing the feed conversion ratio (p < 0.05). All HWS-supplemented groups exhibited markedly lower hepatic lipid accumulation and plasma total cholesterol levels compared with the CON group, accompanied by alleviated hepatocellular steatosis and inflammatory infiltration as revealed by Oil Red O and H&E staining. Moreover, HWS significantly enhanced intestinal microbiota alpha diversity (Ace, Chao, Sobs, and Shannon indices), decreased the relative abundance of the dominant genus Mesomycoplasma, and enriched potentially beneficial genera including Methylobacterium, Delftia, and Sphingomonas (p < 0.05). In conclusion, dietary HWS supplementation effectively improved growth performance, alleviated hepatic steatosis and inflammation, and beneficially reshaped the intestinal microbiota in juvenile largemouth bass fed a FM-free diet. These findings support HWS as a promising functional additive for sustainable FM-free aquafeeds in carnivorous fish species.