Ammonia Excretion Dynamics in Juvenile and Adult Freshwater Prawn Macrobrachium caementarius Reared Under Recirculating Aquaculture Conditions

In this study, total ammonia nitrogen (TAN) excretion rates were quantified in juvenile (mean weight: 1.79 ± 0.17 g) and adult (mean weight: 15.91 ± 0.63 g) prawns (Macrobrachium caementarius) reared under recirculating aquaculture system (RAS) conditions representative of small-scale farming operations. Prawns were fed a commercial dry pelleted diet (48.5% crude protein) at a daily ration equivalent to 5% of total biomass. Water quality parameters were maintained within species-specific tolerance ranges to ensure normal physiological and metabolic function. TAN excretion rates were estimated using a mass balance approach under closed-flow batch conditions. A significant difference in TAN excretion was observed between life stages (p = 0.008): juveniles excreted 0.009 ± 0.006 mg TAN g−1 h−1 (0.22 ± 0.18 mg TAN g−1 day−1), whereas adults excreted 0.03 ± 0.01 mg TAN g−1 h−1 (0.73 ± 0.06 mg TAN g−1 day−1). Distinct diel postprandial patterns were evident in both life stages, with peak TAN release occurring 1–2 h after each feeding event, followed by a gradual decline. These life-stage differences have direct implications for RAS design and biofilter management and should be interpreted in the context of the dietary conditions used. The quantified excretion rates provide baseline bioengineering parameters for sizing biofilters, estimating nitrogen loading, and optimizing water quality management for this emerging aquaculture species.