Food Safety considerations of animal welfare aspects of husbandry systems for farmed fish - Scientific opinion of the Panel on Biological Hazards

Simultaneous determination of antibiotic residues in edible tissue of farmed fish (Oncorhynchus mykiss) from the Umbria and Marche regions

Aquaculture is one of the fastest-growing sectors in global food production, and its expansion has driven the adoption and consolidation of intensive and semi-intensive production methods, which can increase the risk of infectious diseases. The use of various antibacterial compounds for therapeutic purposes has become increasingly common. Monitoring the presence of antimicrobial substances in aquaculture is of the utmost importance to prevent antibiotic resistance and ensure food safety. A multi-residue method was applied to investigate the incidence and the concentration of antibiotic residues in fish flesh collected from Umbria and Marche aquaculture farms over the 4-year period 2020-2023. Due to its rapidity and reliability, this method allowed for the evaluation of 70 antimicrobial molecules in fish flesh and the verification of European Union legislation compliance. Overall, 102 samples were analyzed, and only three antibiotic substances were detected, namely, sulfadiazine, oxytetracycline, and trimethoprim, with a variable presence of positive samples and residue concentration through different seasons, with higher values in winter. The highest value of positive samples was registered in 2021, with 63.2%, followed by 62.2% in 2022 and 51.7% in 2020; 11.1% was registered in 2023. Non-compliant samples were recorded for sulfadiazine (only one at the concentration of 222 μg/kg) and trimethoprim (the concentration ranged from 10 μg/kg to 226 μg/kg). The results indicated that 53.9% of the samples contained residues of authorized substances, with a 6.9% above the respective maximum residue limits.

A novel portable label-free electrochemical immunosensor for ultrasensitive detection of Aeromonas salmonicida in aquaculture seawater

Infectious diseases caused by Aeromonas salmonicida (A. salmonicida) have a huge impact and produce significant losses in aquaculture and fish farming. Fish pathogen early detection is a critical step for the rapid identification and prevention of these problems. This work presents a novel portable label-free ultrasensitive electrochemical immunosensor for A. salmonicida detection in seawater. It consists of a fluidic integrated electrochemical-cell-chip (ECC) with independent chambers enclosing three electrochemical cells (ECs). Anti-A. salmonicida (AbSalm) antibodies were covalently attached to the gold surface of the microfabricated electrodes and were used for the sensitive detection of A. salmonicida. The antibody-antigen immunoreaction was studied by enzyme-linked immunosorbent assay (ELISA), and the surface functionalization was characterized by using quartz crystal microbalance (QCM), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). The performance of the developed immunosensor, in terms of sensitivity, repeatability, and specificity, was also studied. The linear working range varied between 1 and 10⁷ CFU mL^-1, with a limit of detection (LOD) as low as 1 CFU mL^-1. The suitability of the immunosensor for real sample detection was successfully demonstrated via recovery studies performed in spiked seawater samples. The proposed technology supports the use of low-cost and portable instrumentation that concedes the ultrasensitive, simple, and fast quantification of the A. salmonicida. To the best of our knowledge, this is the first portable sensing system for the detection of A. salmonicida in seawater samples, which provides a promising online monitoring platform for the detection of this bacterium in aquaculture facilities.