Abstract

Optimizing oxygen supply and nitrogen removal in recirculating aquaculture systems (RAS) requires species-specific metabolic benchmarks. This study quantified the effects of body size and stocking density on oxygen consumption and total ammonia nitrogen (TAN) excretion in the silverside Odontesthes bonariensis under controlled RAS conditions. A 2 × 2 factorial design was used to compare small (48–140 g) and large (>140–250 g) fish stocked at low (3.2 kg m−3) and high (6.2 kg m−3) densities. Oxygen consumption was significantly influenced by both factors, with mean routine rates ranging from 146.12 ± 35.07 mg O2 kg−1 h−1 in high-density large fish to 226.31 ± 50.71 mg O2 kg−1 h−1 in low-density small fish. Smaller fish exhibited higher mass-specific rates, and individuals held at lower densities consumed more oxygen, consistent with allometric scaling and density-dependent metabolic suppression. In contrast, TAN excretion was unaffected by size or density, with mean values ranging from 4.59 ± 0.77 to 10.81 ± 3.76 mg TAN kg−1 h−1 across treatments, indicating stable protein catabolism under a uniform feeding regime. Both parameters displayed pronounced diurnal fluctuations, with postprandial peaks associated with specific dynamic action: oxygen consumption fluctuated between 61.75 and 333.03 mg O2 kg−1 h−1, while TAN excretion ranged from 0 to 78.63 mg TAN kg−1 h−1 over 24 h cycles. These findings demonstrate that oxygen demand in O. bonariensis is strongly modulated by bioenergetic scaling and stocking density (ranging from 146 to 226 mg O2 kg−1 h−1), whereas ammonia excretion (4.6–10.8 mg TAN kg−1 h−1) is primarily driven by dietary input. These results provide species-specific baseline benchmarks for aeration sizing and biofilter design, thereby supporting the sustainable intensification of silverside aquaculture in RAS.

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