The use of bacterial and microalgal consortia to remove nitrogen from wastewater has garnered attention as a potential alternative to conventional systems. This approach not only reduces energy consumption but also aids in nutrient recovery. Light is essential for algae photosynthesis; however, nitrifying bacteria are also influenced by light radiation. This mini-review summarizes the current knowledge concerning photoinhibition, the light stimulation of ammonia-oxidizing bacteria (AOB), resistance to light radiation, the implementation of microalgal–bacterial systems, and the possible mechanisms involved. Nitrosomonadaceae AOB and Nitrospiraceae nitrite-oxidizing bacteria (NOB) often coexist in a microalgal–bacterial system. Studies have suggested that AOB can tolerate light radiation at 200 μmol m⁻²·s⁻¹ in microalgal–bacterial systems, whereas NOB are almost completely suppressed, which can result in partial nitrification in the bioreactor. An appropriate light level can stimulate AOB growth in microalgal–bacterial granular reactors and may improve algae metabolic activity. Granular sludges or artificial “light-shielding hydrogel” could effectively protect nitrifying bacteria from light intensities up to 1600 μmol m⁻²·s⁻¹ in wastewater treatment reactors. Microalgal–bacterial systems along with the associated “algal shading effect” have been widely used in pond aquaculture. This approach minimizes the need for costly mechanical aeration through photo-oxygenation and facilitates nutrient recovery by filter-feeding fish.

Pond aquaculture is an important aquacultural model worldwide in which ammonia-oxidizing bacteria (AOB) are crucial for the removal of ammonia from water. The influence of light irradiation on AOB in an aquaculture pond was studied using artificial simulation wastewater under dark/light cycles of 24 h/0 h (L0), 12 h/12 h (L12), and 0 h/24 h (L24). The ammonia oxidation rates (AORs) in groups L0, L12, and L24 were 9.88 ± 0.19 mg h⁻¹, 6.01 ± 0.32 mg h⁻¹, and 1.85 ± 0.09 mg h⁻¹, respectively. Long-term exposure to light had a serious impact on the AOR and decreased the abundance of Nitrosomonas spp. and their ammonia monooxygenase genes. To determine the protective effect of microalgae on AOB, different doses of freeze-dried Chlorella spp. powder were added to the nitrifying bacteria community. The photoinhibition rate of chlorophyll a (Chla) in the groups with 300 and 1300 µg L⁻¹ of added Chlorella were 32.85% and 28.77%, respectively, while the Chla in the 2200 µg L⁻¹ Chlorella-added group was only 0.01%, with no significant differences (p > 0.05) in AOR between the dark/light treatment subgroups. Fluorescence in situ hybridization showed that AOB, nitrite-oxidizing bacteria, and algae coexist and grow together without free AOB in the nitrifying bacterial community. It was suggested that microalgae enhance the resistance of AOB to light irradiation in a pond through the shading effect provided by algal chlorophyll and the close symbiotic relationship between microalgae and AOB.

The existing vacuum fish pump is too large and difficult to move, which is difficult to apply to small fishing vessels. However, the development of a small vacuum fish pump is not a single scaling of the existing vacuum fish pump but requires the support of relevant experiments and simulation theories. In this study, a vacuum fish pump suitable for small fishing vessels was developed. Firstly, a numerical model of the internal flow field during the vacuum fish pump’s working process was established using computational fluid dynamics (CFDs) and verified its effectiveness by physical experiments. It is found that the VOF model can well predict the variation of the volume fraction of the liquid phase in the whole calculation area with time during the suction or drainage process of the vacuum fish pump. Then, the internal flow field characteristics of the fish pump under different working conditions were simulated, and the rationality of the design of the fish pump was evaluated according to the numerical results. Finally, a separate physical experiment was carried out on grass carp, carp, crucian carp, silver carp, and bighead carp, respectively, and the capture efficiency and corresponding fish damage rate for different fish were analyzed. The experimental and numerical results show that the vacuum suction fish pump can achieve efficient and automatic suction and transport of live fish.

Aquaculture effluent commonly contains residual suspended solids, inorganic nitrogen, reactive phosphorus and algal biomass, creating a need for low-cost ecological treatment strategies. This study evaluated the effects of Bellamya stocking density on water quality and bacterial community responses in aquaculture effluent. A no-snail control (CON) and four Bellamya stocking-density treatments (LD, MD, MHD and HD) were established with three independent replicates per group. Suspended solids (SS), NH₄⁺-N, NO₂⁻-N, NO₃⁻-N, PO₄³⁻-P and chlorophyll-a (Chl-a) were measured, and bacterial communities were characterized by 16S rRNA gene sequencing of the V3–V4 region. Bellamya stocking-density treatments significantly reduced NH₄⁺-N and NO₃⁻-N, while the HD and MHD treatments also showed lower PO₄³⁻-P and Chl-a. SS showed a downward tendency, whereas NO₂⁻-N tended to increase, suggesting possible transient accumulation of a nitrogen-transformation intermediate. Alpha diversity differed among treatments, and Bray-Curtis NMDS demonstrated a marked treatment-related shift in bacterial community structure (PERMANOVA R² = 0.62, P = 0.001; stress = 0.0822). At the genus level, Rhodobacter, Ahniella, Novosphingobium, Sphingobacterium and Silanimonas displayed distinct treatment responses, consistent with LEfSe-based biomarker analysis. Spearman correlation and redundancy analysis further showed that selected bacterial genera were closely associated with nitrogen, phosphorus and Chl-a gradients. Overall, Bellamya stocking-density treatments improved several eutrophication-related water-quality indicators and reshaped the effluent bacterial community. The results support Bellamya stocking-density management as a potential ecological component of aquaculture effluent management, while the microbiome results should be interpreted as community-level associations rather than direct evidence of microbial causality.

Aquaculture effluent commonly contains suspended solids, inorganic nitrogen, reactive phosphate and algal biomass, creating a need for low-input ecological treatment approaches. This study assessed endpoint water-quality and bacterial-community responses to Bellamya stocking density in aquaculture effluent. A no-snail control (CON) and four stocking-density treatments (LD, MD, MHD and HD) were established with three independent tank replicates per treatment. Suspended solids (SS), NH₄⁺-N, NO₂⁻-N, NO₃⁻-N, PO₄³⁻-P and chlorophyll a (Chl-a) were quantified, and bacterial communities were characterized by 16S rRNA gene sequencing of the V3–V4 region. At the 60-day endpoint, all Bellamya-stocked treatments had lower NH₄⁺-N and NO₃⁻-N concentrations than the control, and MHD and HD also had lower PO₄³⁻-P and Chl-a. SS showed a nonsignificant downward tendency, whereas NO₂⁻-N showed a nonsignificant upward tendency. Bray–Curtis NMDS visualized treatment-associated separation, and PERMANOVA detected significant differences among treatments (R² = 0.62, p = 0.001; stress = 0.0822). However, PERMDISP was also significant (F_4,10 = 4.99, p = 0.001), indicating heterogeneous within-treatment dispersion and requiring cautious interpretation of the PERMANOVA result. Representative genera showed distinct treatment-associated abundance patterns, and 46 of 90 genus–environment associations remained significant after Benjamini–Hochberg correction. Predicted KEGG Level 3 pathways varied numerically among treatments, but none remained significant after false-discovery-rate correction. These findings indicate that Bellamya stocking may provide a low-input ecological component of aquaculture-effluent management, while the microbiome results should be interpreted as community-level associations and predicted functional trends rather than evidence of microbial causality or pathway activation.