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.

The aim of this study was to investigate the effect of different carbon sources on the water quality, microorganisms, proximal composition, floc size, and growth performance of Cryphiops caementarius in the biofloc system. In each treatment, carbon sources (molasses and chancaca), and control were randomly assigned in triplicate. Shrimp with an initial body weight of 24.28±0.44 g were stocked in 9 rectangular fiberglass tanks with a water volume of 150 L for 142 days. They were fed a commercial diet containing 48.5% crude protein at a rate of 5% of their body weight. A C/N ratio of 15 was maintained across all treatments. Water quality parameters remained within suitable concentration ranges for C. caementarius throughout the study. Overall, the results indicated that both molasses and chancaca can be used as carbon sources for the control of nitrogenous compounds without affecting production indices. However, these carbon sources may have a significant effect on the composition of the microbial community and the size and composition of the biofloc, suggesting that the choice of carbon source used in biofloc technology (BFT) plays a significant role. BFT appears to be an effective tool for freshwater shrimp producers due to its water efficiency, particularly in arid regions.

Biofloc technology (BFT) is based on the reutilization of nitrogenous waste generated by cultured organisms through the biotransformation of these compounds primarily into microbial biomass, allowing a reduction in water exchange. The aim of this study was to evaluate BFT as a water-saving culture strategy, using two carbon sources (chancaca and molasses), and to assess its effects on water-use efficiency, growth performance, digestive enzyme activity, and physiological responses in juvenile northern river shrimp (Cryphiops caementarius). The experiment was conducted in triplicate using 400 L fiberglass tanks, with an initial stocking density of 75 shrimp m⁻² and an average individual weight of 0.85 ± 0.65 g, over a 157-day rearing period. Water quality parameters were maintained within suitable ranges throughout the study. Significant differences were observed in the composition of bacterial and plankton communities among the biofloc treatments, whereas no significant differences were detected in growth performance or digestive enzyme activities. Heat shock protein 70 (Hsp70), a stress-related biomarker indicative of physiological responses, exhibited higher levels in the biofloc treatment supplemented with molasses. Overall, BFT treatments reduced water exchange by 81.6% while maintaining comparable biological performance to the control, indicating that biofloc technology represents a water-efficient and environmentally sustainable culture approach for juvenile Cryphiops caementarius, an endemic freshwater shrimp species, particularly in water-limited regions of northern Chile.

The Chilean silverside (Basilichthys microlepidotus) is an endemic freshwater species considered Vulnerable, and the species-specific bioengineering parameters needed to design efficient recirculating aquaculture systems (RAS) for this species, particularly oxygen consumption, remain unknown. A factorial experiment (2 × 2) was conducted to evaluate how body size and stocking density affect the routine oxygen consumption of B. microlepidotus. The study considered two body-size groups and two stocking-density treatments, each represented by three replicate tanks. Oxygen uptake rates were determined from mass-balance calculations in a static closed respirometry system during sequential 24 h periods. Body size significantly influenced mass-specific oxygen consumption, with smaller fish exhibiting higher rates than larger fish, consistent with allometric metabolic scaling, whereas no significant independent effect of stocking density was detected; however, with only three tanks per treatment and two similar densities, the test had low power and this result is inconclusive. A pronounced diurnal pattern was evident in all treatments, with the main oxygen consumption peak near 14:00 h, approximately three hours after the single daily feeding (11:00 h), which is consistent with, but does not demonstrate, a specific dynamic action (SDA) response because no unfed control was included; a smaller peak near 08:00 h preceded feeding and may reflect routine laboratory activity at the start of the working day. These results provide the first species-specific reference values of routine oxygen consumption for B. microlepidotus, offering a preliminary basis, within the size and density ranges tested, for estimating the oxygen demand of fish in RAS designed for this species, with direct relevance for both conservation-oriented restocking and its development as a candidate for freshwater aquaculture diversification.