Aquaponics of the water caltrop (Trapa natans L.) with African catfish (Clarias gariepinus Burchell, 1822) using sheep's wool in a novel submerged gravel pot cultivation system

Aquaponics is a sustainable agriculture method in which aquaculture-derived nutrients support plant growth, thereby addressing food security and promoting resource efficiency. This study aimed to evaluate the potential of the European water caltrop ( Trapa natans) as a novel aquaponic crop using African catfish ( Clarias gariepinus ) as the nutrient source. A new submerged throughflow gravel pot hydroponic system, with local sheep wool as substrate, was developed. Three nutrient treatments were applied, namely sheep wool with tap water (SW+KW), sheep wool soaked in fish faeces (SW+FF) and sheep wool with aquaculture process water (SW+FW). SW+FW initially developed but died early, resulting in reproductive failure. SW+FF produced the highest rosette numbers, largest rosettes, heaviest fruits and tended to yield more fruits per rosette and compartment, whereas SW+KW showed lower growth and reproduction. Minor differences in water temperature and dissolved oxygen were observed among treatments. Nutrient concentrations, conductivity, and salinity varied strongly, being lowest in SW+KW, intermediate in SW+FF, and highest in SW+FW, with values increasing over time. Plant performance reflected these treatment-specific hydro-chemical conditions. SW+FF supported optimal growth and reproduction due to balanced nutrient availability and tolerable salinity, SW+KW was constrained by nutrient limitation, and SW+FW, the most nutrient-rich and more saline treatment, failed. Overall, this approach enabled successful indoor cultivation of T. natans under aquaponic conditions, completing a full reproductive cycle from germination to fructification, demonstrating the species’ potential for aquaponics. Recommendations for future system optimization are provided, and key hydro-chemical requirements are highlighted to inform conservation and management strategies.