This study aimed to evaluate and compare the effects of biofloc technology (BFT) and clear water (CW) on water quality physiological and productive performance of juvenile freshwater Northern River shrimp, Cryphiops caementarius under three stocking densities (100, 200, and 400 shrimp m⁻²). Shrimp with an initial body weight of 0.44 ± 0.07 g were stocked in 18 rectangular fiberglass tanks with a water volume 150 L for 290 days. During the experiment, water quality parameters stayed within acceptable ranges for shrimp growth. The highest survival rate was recorded in BFT treatments; however, the growth performance of shrimp in the treatments with the lowest stocking density was higher than that with the highest stocking density, regardless of whether BFT or CW was used. Transcriptional levels of heat shock protein (Hsp70) and superoxide dismutase (SOD) showed significant differences (p < 0.05) between treatments, particularly in BFT. These results indicate that an initial stocking density of 200 shrimp m⁻² appears to be appropriate for shrimp juveniles cultured in a BFT system. Thus, this technology emerges as an effective tool for river shrimp farmers looking to increase their stocking densities and improve the efficiency of their production systems in arid zones.

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.

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.