The expanding global demand for sustainable aquaculture underscores the need for efficient water quality management, particularly in controlling harmful nitrogenous compounds like nitrites. This study explores the effectiveness of Pantoea sp. A5, a nitrite-degrading bacterium isolated from food waste, reduces nitrite levels in aquaculture systems, focusing on the role of carbon sources like glucose and glycerol. The experiments showed that these carbon sources, especially glycerol, significantly enhanced the bacterium's ability to degrade nitrites across a range of temperatures without promoting growth, suggesting a cost-effective alternative to glucose. Unlike acetic acid, which did not enhance nitrite degradation, glycerol and glucose regulated metabolic pathways, evidenced by reduced malate dehydrogenase (MDH) activity and increased glutamate dehydrogenase (GDH) levels, facilitating efficient ammonia assimilation. These findings highlight the potential of using targeted carbon sources to manage nitrite levels in aquaculture, improving sustainability and contributing to global food supply efforts.

Nitrite accumulation is a major water quality problem in intensive aquaculture because it impairs oxygen transport and threatens the health and survival of cultured organisms. The denitrification performance of Shewanella algae MB-1 was evaluated under seawater conditions, with particular attention to the effects of ionic composition on its activity. MB-1 completely removed 20 ppm nitrite in LB medium over a broad salinity range from 0.5% to 7% NaCl, whereas both growth and denitrification activity were severely impaired at 0% and 9% NaCl. Most ionic compounds tested at 0.5% and 1%, including K2HPO4, NaH2PO4, KH2PO4, MgCl2, KCl, Na2HPO4, Na3C6H5O7, and NH4Cl, supported substantial growth and complete denitrification, whereas CaCl2 and Ca(CH3COO)2 did not. Under seawater conditions, resuspension chemistry strongly affected functional performance. MB-1 cells resuspended in 1×PBS reduced nitrite after 24 h and completely removed it after 48 h, whereas cells resuspended in 0.5%, 1%, or 2% NaCl showed no detectable denitrification activity. Intracellular nitrite measurements showed that cells resuspended in 1×PBS accumulated substantially more intracellular nitrite than NaCl resuspended cells, particularly after 48 h. Consistently, nrfA expression was detected only in the 1×PBS resuspended group. Together, the results show that ionic composition strongly influences denitrification by MB-1 and that intracellular nitrite availability is closely associated with activation of the nitrite reduction pathway. These findings provide a mechanistic basis for developing MB-1 as a functional bacterium for sustainable water quality management in seawater aquaculture.

Red coloring determines the commercial value of blood parrot cichlids (Vieja melanurus × Amphilophus citrinellus). While synthetic astaxanthin (SA) is commonly used to improve hue, its expensive cost has prompted the quest for more sustainable alternatives. This 60-day study looked at shrimp waste extract (SWE) as a dietary supplement for color improvement. Fish were assigned to five diets: basal control (G1, 0 mg/kg SA: 0 mg/kg SWE), SWE alone (G2, 0 mg/kg SA: 7.7 mg/kg SWE), high SA (G3, 90 mg/kg SA: 0 mg/kg SWE), moderate SA (G4, 45 mg/kg SA: 0 mg/kg SWE), and mixed SA with SWE (G5, 45 mg/kg SA: 7.7 mg/kg SWE). Growth and CIELAB skin pigmentation were evaluated. Growth performance was consistent across all treatments. Colorimetric study found that while the SWE alone (G2) significantly improved pigmentation compared to the control, it was less effective than the high-SA diet. However, incorporating SWE into the moderate-SA diet (G5) resulted in a promising complementary response. Despite having half the SA concentration, G5 achieved pigmentation that was comparable or superior to the G3 diet by the end of the feeding trial. These data revealed that, while SWE has lower independent activity, it is an effective complementary additive for shortening the feeding period required to achieve a similar redness. Finally, SWE enables the partial substitution of synthetic astaxanthin, providing a cost-effective and environmentally sustainable nutritional strategy for the ornamental aquaculture business.