Impact of biofilm support media on microbial dynamics, rocket (Eruca vesicaria subsp. sativa) growth, and antioxidative content in aquaponics

Aquaponics integrates aquaculture and hydroponics into a recirculating system where fish-derived nutrients sustain plant growth. The efficiency of this process relies heavily on the biofilm support media that facilitate microbial activity and nutrient transformation. This study evaluated the performance of biochar and clay pebbles as biofilm substrates in a Nutrient Film Technique (NFT) aquaponic system cultivating rocket (Eruca vesicaria subsp. sativa) with tilapia (Oreochromis niloticus). Over a two-month trial, biochar significantly enhanced nitrogen mineralization, increasing nitrate concentrations from 0.24 to 0.34 mg·L⁻¹. Microbiological assessments confirmed the absence of pathogenic bacteria in both systems, while biochar promoted higher populations of nitrifying microorganisms. Plant physiological and biochemical traits were strongly influenced by the substrate type: biochar increased dry biomass, nitrogen content, photosynthetic pigments, soluble proteins, and sugars, whereas clay pebbles favored the accumulation of carotenoids and secondary metabolites including phenolics, flavonoids, and tannins. Overall, biochar improved water quality and nutrient availability, resulting in enhanced rocket productivity, while clay pebbles contributed to superior nutritional and antioxidant properties. These findings highlight the importance of biofilter media selection for optimizing both yield and nutritional quality in aquaponic production systems.