Introduction
Lettuce (Lactuca sativa), pak choi (Brassica rapa subsp. chinensis), and cherry tomato (Solanum lycopersicum var. cerasiforme) were cultivated in greenhouse aquaponic systems at Sultan Qaboos University. Tilapia (Oreochromis niloticus) reared in the system were also analysed. Equivalent market samples were purchased for comparison. Crop and fish samples were analysed for microbiological quality, heavy metals, pesticide residues, and macro- and micronutrient composition. Additional analyses of fish feed, source water, aquaponic water, and hydrostones were conducted to better understand nutrient pathways and possible contamination sources.
Materials and methods
Lettuce (Lactuca sativa), pak choi (Brassica rapa subsp. chinensis) and cherry tomato (Solanum lycopersicum var. cerasiforme) were cultivated in greenhouse aquaponic systems. Tilapia (Oreochromis niloticus) from the aquaponic system were also analysed. Market samples of the same products were purchased for comparison. Crop and fish samples were analysed for microbiological quality, heavy metals, pesticide residues, and macro- and micronutrient composition. Supporting analyses were also conducted on fish feed, source water, aquaponic water and hydrostones to better understand nutrient dynamics and possible contamination pathways within the system.
Results and discussion
Across all vegetable samples, Escherichia coli, Salmonella, and Listeria monocytogenes were not detected, while Staphylococcus aureus occurred only in lettuce at very low levels, not associated with toxin formation. Heavy metals were below detection limits and pesticide residues were below the limit of quantification in all crop samples. Nutritional differences were crop-specific. Aquaponic lettuce contained higher magnesium, calcium, potassium, sulphur, and iron, whereas market lettuce contained higher nitrogen, phosphrous and nitrate. In cherry tomato, aquaponic fruits had higher Phosphrous but lower calcium, zinc, and iron than market fruits. Pak choi showed the fewest differences, with only magnesium and total nitrogen differing significantly between sources. Tilapia from both aquaponic and market sources showed a favourable microbiological profile. Supporting analyses further showed that fish feed contained no detectable heavy metals and no quantifiable pesticide residues, while source water and aquaponic water showed no detectable heavy metal or pesticide contamination. Source water also showed a favourable microbiological profile, and hydrostones contained high iron but no detectable arsenic, lead, cadmium or mercury.
Overall, aquaponics produced foods with strong microbiological and chemical safety and nutritional profiles broadly comparable to market products. The findings further suggest that leafy vegetables may be better suited than fruiting crops to low-input coupled aquaponic systems, where nutrient supply may not fully match the higher demands of fruit production. These results support the potential of aquaponics as a sustainable food-production strategy for arid and water-limited regions.
Acknowledgment
We gratefully acknowledge Dr. Ahmed Al-Souti for his support and Mr. Said Al-Harthi for assistance in the greenhouse. We also thank Mr. Saleh Mohammed Al-Shargi and Mr. Akbar Khan for greenhouse maintenance.
References
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