Preliminary investigation on the occurrence and health risk assessment of antibiotics in cultured tilapia retailed at a commercial outlet in Tema, Ghana.

In Ghana, Nile tilapia is one of the most commonly cultivated fish species. Bacterial infections, which mostly occur in intensive fish farming, are considered to be the most significant health issue facing these culture systems in Ghana's aquaculture industry. To prevent, and treat bacterial infections and promote fish growth, antimicrobials are often used, and in most cases at unregulated doses. However, this misuse and neglect of withdrawal durations for such antimicrobials may result in drug residues showing up in fish edible tissue, posing a risk to human consumers. To evaluate the risk to consumers, this study screened for antibiotic residues in popular tilapia fish sold at a retail outlet in Tema. Using ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC/MS/MS), the study analysed the levels of 12 antibiotics present in 24 tilapia samples sold at a retail outlet in Tema. Erythromycin, tetracycline, oxytetracycline, and amoxicillin were detected at varying levels, with frequencies of 20.8 %, 62.5 %, 58.3 %, and 54.2 %, respectively. The highest concentration of 3.521 ± 0.32 µg/kg was found for oxytetracycline, while erythromycin had the lowest concentration (0.276 ± 0.11 µg/kg) in the samples. According to the study, the levels of antibiotics detected in the sampled tilapia were lower than the maximum residue limits (MRL) recommended by the WHO. Additionally, both the hazard quotient (HQ) and hazard index (HI) values were less than one. Therefore, consuming retail farmed tilapia purchased from the commercial outlet in Tema metropolis was deemed to pose no significant risk to human health. However, regular monitoring of antibiotics and other contaminants is necessary to minimise their potential impacts on human health.

16S rRNA Gene Sequence Identification of Cultivable-Bacterioplankton Between Ambient Water and Gastrointestinal Tract (GIT) of Resident Teleost.

This study was conducted to evaluate the ambient water bacterial dynamics and its influence on the gut of resident teleosts; Oreochromis niloticus. The bacterial communities in the ambient water and the gastrointestinal tract (GIT) of O. niloticus were profiled using a culture-dependent method and followed by the 16S rRNA gene sequencing. The results indicated bacterial phyla of Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes respectively between the two microbial consortia. However, the relative abundance among the bacterial phyla notably differed between the two consortia. The relative abundance of Proteobacteria (≤ 67%) was dominant in both consortia, but contrarily, Actinobacteria and Bacteroidetes were higher in the ambient water relative to the GIT which indicated Proteobacteria and Bacilli as the highest diversity. Nevertheless, the relative abundance of γ-proteobacteria and Bacilli remarkably dominated both consortia at the class level, with Bacillus and Pseudomonas being the most abundant operational taxonomic units (OTUs).

Antibacterial activity of Mallotus japonicus (L.F.) Müller Argoviensis on growth of Aeromonas hydrophila, A. salmonicida, Edwardsiella tarda and Vibrio anguillarum.

AIMS: The present study evaluated the antimicrobial activities of the medicinal plant Mallotus japonicus against the fish pathogenic bacteria, Aeromonas hydrophila, Aeromonas salmonicida, Edwardisella tarda and Vibrio anguillarum, and also describes the antimicrobial activities of the major and minor active compounds present within the plant extract. The synergistic effects by way of combination of these compounds were also evaluated and described. Chemical constituents of the plant extracts were analysed using the liquid chromatography-mass spectrometry (LC-MS) and described. METHODS AND RESULTS: The diethyl ether-extract of the plant elicited the strongest antibacterial activity against the challenged bacterial species, followed by ethanol- and methanol-extracts. The major active compound of the extracts, bergenin, demonstrated no antibacterial activity, but other compounds in the extracts did. CONCLUSION: Mallotus japonicus could be used as a prophylaxis to treat bacterial disease infections of fishes and its diethyl ether-extract has the potential of an alternative to antibiotic treatment in aquaculture. SIGNIFICANCE AND IMPACT OF THE STUDY: Mallotus japonicus diethyl ether-extract has the potential of an alternative to antibiotic treatment in aquaculture.