Sustainable Development of Water Quality, Growth, and Production Efficiency of the Giant Mottled Eel (Anguillamarmorata) at Different Stocking Densities in the Indoor Media-Based Aquaponics System

The sustainability of aquaponic systems, particularly regarding <i>Anguilla marmorata</i> 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 <i>A. marmorata</i> in a media-based indoor aquaponics system cultivated with <i>Brassica rapa</i> var. <i>pekinensis</i>. The 8-week trial tested stocking densities of 10 (T₁), 15 (T₂), and 20 (T₃) eels 250 L^-1, each with three replicates. Significant differences (<i>p</i> < 0.05) were observed in water parameters and nutrient accumulation, with higher densities linked to greater nutrient availability. Growth performance indicated that T₂ achieved the best overall results, with significantly higher weight gain, specific growth rate, and feed efficiency and the lowest feed conversion ratio of <i>A. marmorata</i> and enhanced plant growth (<i>p</i> < 0.05). T₁ showed the highest protein efficiency ratio, while T₃ yielded the highest biomass per volume. Moisture and crude protein contents were highest in T₃, whereas crude lipid and ash contents were highest in T₁ and T₂, respectively (<i>p</i> < 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.