Abstract
The sustainability of aquaponic systems, particularly regarding Anguilla marmorata productivity and water quality, is strongly influenced by stocking density. This study investigated the effects of different stocking densities on water quality, growth performance, and the proximate composition of A. marmorata in a media-based indoor aquaponics system cultivated with Brassica rapa var. pekinensis. The 8-week trial tested stocking densities of 10 (T(1)), 15 (T(2)), and 20 (T(3)) eels 250 L(-1), each with three replicates. Significant differences (p < 0.05) were observed in water parameters and nutrient accumulation, with higher densities linked to greater nutrient availability. Growth performance indicated that T(2) achieved the best overall results, with significantly higher weight gain, specific growth rate, and feed efficiency and the lowest feed conversion ratio of A. marmorata and enhanced plant growth (p < 0.05). T(1) showed the highest protein efficiency ratio, while T(3) yielded the highest biomass per volume. Moisture and crude protein contents were highest in T(3), whereas crude lipid and ash contents were highest in T(1) and T(2), respectively (p < 0.01). These findings suggest that a moderate stocking density (15 eels 250 L(-1) of water) optimizes fish and plant growth, system sustainability, and nutrient utilization in small-scale aquaponic systems.