One major source of antibiotic contamination in the sea is from aquaculture. We monitored concentration of commonly used antibiotic classes and antibiotic resistance genes (ARGs: tet(M), sul1, sul2 and sul3) in seven main aquaculture production stations in Peninsular Malaysia and detected twenty-three antibiotics. Tetracyclines, sulfonamides and quinolones were the most frequently detected antibiotic classes, 2 indicating a wide distribution of antibiotics in Malaysian aquaculture farms.Oxytetracycline, tetracycline and minocycline were the common tetracyclines (LOQ-2.45× 10 2 ng/L) detected, while sulfamerazine and sulfathiazole were commonly detected sulfonamides (LOQ-2.82× 2 ng/L) among the farms. For quinolones (LOQ-9.58 × 10 5 ng/L), enrofloxacin, nalidixic acid, and ofloxacin were the most 31 common. Relative to Asian aquaculture farms, the residues detected here were at low 32 or moderate levels except for quinolones. The dendrogram and heatmap revealed 33 three groups of antibiotic concentration patterns but with no differences in the types of antibiotics usage among aquaculture farms were observed. The ARGs (10 -3 copies/16S) were detected in more than 90% of the sites except for sul3. There was also high ecological risks of ciprofloxacin, enrofloxacin, norfloxacin and lincomycin for cyanobacteria and algae in Kelantan, Perak and Pahang. This is the first study to shed light on the antibiotic contamination, ARGs in aquaculture systems and its potential ecological risk in the coasts of Malaysia. This study will be useful to develop effective management of aquaculture wastewater in order to mitigate antibiotic pollution and transmission of ARGs to humans through the food chain.

The indiscriminate use of antibiotic in aquaculture and leaching of antibiotic from aquaculture to the environment may led to the emergence and spread of antibiotic resistant bacteria and their resistant genes which is a public concern. Five tetracycline antibiotics (minocycline, doxycycline, chlorotetracycline, oxytetracycline and tetracycline) and 14 types of tetracycline genes, tet[(A), (B), (C), (D), (E), (G), (K), (L), (M), (O), (S), (P), (Q) and (X)], were investigated in waters from five marine aquaculture farms in Peninsular Malaysia. Tetracycline was detected in low concentrations from <LOQ to 25.6 ng/L. A total of 93 isolates of bacteria were isolated whereby Vibrio (n=29) and Pseudoalteromonas (n=7) were the predominant bacteria. Forty-eight of the isolates carried tet genes with 22.9% encoded multiple tet genes and 72.9% encoded a single tet gene. tet(A) (n = 20, 42%) was the most prevalent gene followed by tet(B) (n = 14, 29%) and tet(K) (n = 13, 27%). A few common tet carriers (Enterobacter, Vibrio, Photobacterium, and Pseudoalteromonas) carrying tet genes that have not been reported were identified. The values of the risk quotients (RQs) of tetracycline in Matang was 0.28 which posed a medium ecological risk to algae. Thus, the antibiotic residues in the aquaculture farm in Matang need to be monitored closely.