WITHDRAWN: A comparison of the effect of starting nitrate concentration on fish growth, plant production and water quality within a research-scale, recirculating aquaponics system

Abstract

Abstract Murray Cod, Maccullochella peelii peelii, and Green Oak lettuce, Lactuca sativa, were used to determine the effects of three different starting nitrate concentrations, in a research-scale aquaponic system using gravel bed hydroponic components: control (initial nitrate = 0 mg/L), medium nutrient (initial nitrate = 25 mg/L) and high nutrient (initial nitrate = 50 mg/L), where plant nutrients were supplied from fish wastes while the plants removed nutrients from the water before it was returned to the fish tanks (25.9 g of fish feed/m2 of plant growing area/day). Murray Cod had FCR's and biomass gains that were statistically identical in all systems (mean SGR = 1.16%/replicate/day; mean FCR = 0.84). Lettuce, in terms of biomass gain and yield, within both the medium and high nutrient treatments (medium yield of 4.28 kg/m2 and high yield of 4.41 kg/m2) had superior results when compared to the control (yield of 3.47 kg/m2). In terms of nitrate removal (nitrate accumulation: control = 5.60 mg/L; medium nutrient = - 0.50 mg/L; high nutrient = - 1.57 mg/L) and phosphate removal (phosphate accumulation: control = 0.92 mg/L; medium nutrient = - 5.53 mg/L; high nutrient = - 9.04 mg/L), conductivity accumulation (control = 237 μS/cm; medium nutrient = 186 μS/cm; high nutrient = 189 μS/cm), pH, buffer additions (control = 0.7 g/day; medium nutrient = 0.9 g/day; high nutrient = 0.9 g/day) and water use (control = 1.15 L/day; medium nutrient = 0.98 L/day; high nutrient = 1.04 L/day), no statistical difference was observed between any treatments. Overall, results demonstrate that starting nitrate concentrations (with nutrients derived from fish wastes) between 25 mg/L and 50 mg/L provided improvements in the research-scale aquaponic system for plant yield. This study demonstrates nutrient levels should be allowed to accumulate in coupled aquaponic systems by feeding fish for a few weeks before plants are introduced.