Aquaponics (AP) and biofloc technology (BFT) systems rely heavily on bacterial communities to break down organic matter and cycle nutrients that are essential for fish and plant growth. The functional roles of bacterial communities in aquaculture systems are critical to their sustainable operation. Currently, the research on the combination of BFT and AP systems called FLOCponics (FP) is lacking, thereby hindering our ability to optimize their performance. Here, several characteristics (productivity of fish and crops, physicochemical properties of water, and bacterial community) in FP systems cultivating Japanese eel (Anguilla japonica) and leaf lettuce Caipira (Lactuca sativa) were compared to those in the BFT system. Additionally, the effect of fish density on the FP system was investigated. The results indicated that the FP system was more productive than the BFT system. Fish growth rate was highest in the FP system (52.6%), and the average body weight of eels was 168.2 ± 26.8 g in the FP system compared to 140.3 ± 27.0 g in the control (BFT, 5 kg/m²). However, increasing fish density resulted in lower growth rates, with a growth rate of 20.6% observed in the high-density (20 kg/m²) experimental group. The bacterial composition was also significantly different between the systems and fish densities, suggesting that bacterial communities may be closely related to the performance of the aquaponics system.

Interest in aquaponics (AP) is increasing due to its ability to minimize sewage and maximize feed efficiency in fish farming. However, owing to limitations of intensive cultures and a lack of nutrients such as NO₃ for growing crops, AP requires the use of artificial nutrients. Therefore, novel approaches are required to develop AP-intensive culturing methods. An AP system based on biofloc technology (BFT) called FLOCponics (FP) has been recommended. Here, the productivity of the weather loach (Misgurnus anguillicaudatus) in the FP system, BFT system, and flow-through systems (FTSs), as well as these systems’ effect on Caipira lettuce (Lactuca sativa) growth, was analyzed. To compare crop productivity, a hydroponic (HP) bed was installed. The growth rate of M. anguillicaudatus showed significant differences, at 51.1 ± 3.69% in the FP system, followed by 24.0 ± 4.16% in the BFT system and −14.3 ± 1.4% in the FTS. Its survival rates were better in the FP system (91.1 ± 2.64%) than in the BFT system (82.1 ± 10.98%) or the FTS (66.8 ± 2.75%) (p < 0.05). Total ammonia nitrogen and NO₂⁻-N concentrations were stabilized in every plot during the experimental period. However, the NO₃⁻-N concentration continuously increased in the BFT system but decreased in the FP system and was maintained. The shoot weight of the Caipira lettuce was 163.6 ± 8.65 g in the FP system and 149.6 ± 9.05 g in the HP system. In conclusion, FP system can provide a large amount of nutrients and improve the growth performance of both fish and crops in the FP system.

Biofloc technology (BFT) systems heavily rely on microbiota to mitigate ammonia toxicity and manage essential nutrient cycling. Understanding the diversity and functional role of microbiota within BFT-applied aquaculture systems is crucial for ensuring sustainable operations. Though some studies exist on BFT microbiota, research on microbial differences in Japanese eel aquaculture is still limited, hindering the wider application of BFT systems. In this study, we analyzed the characteristics of water quality factors and microbiota in Japanese eel (Anguilla japonica) breeding water, applying the BFT system. Using a metabarcoding approach, the diversity and community structure of aquatic microbiota were compared between BFT and continuous flow (CF) systems. The pH was significantly higher in CF water, while total ammonia nitrogen (TAN) and nitrite (NO₂⁻-N) was higher in BFT water. Alpha diversity was significantly higher in BFT compared to CF systems, and it was correlated significantly with pH and TAN. In both BFT and CF water, the phyla Proteobacteria and Bacteroidota were found to be the most abundant. In the BFT water, a diverse array of bacterial taxa, including BFT-specific clades, were consistently present, while the microbiota in CF water was more variable and contained fewer specific taxa. In addition, bacterial functions related to nitrate reduction, sulfur compound oxidation, and chitinolysis were significantly more abundant in BFT than in CF systems. These findings highlight differences in water quality and microbiota between aquaculture systems, which can inform future research on the use of BFT for sustainable fish farming.

The disease-causing koi herpes virus (KHV), also known as cyprinid herpesvirus-3 (CyHV-3), causes mass mortality of koi and carp. Koi (Cyprinus carpio) is a host for KHV, one of 12 virus species in the Alloherpesviridae family. We examined the effects of KHV disease koi (KK), and on koi×red common carp (KR) and red common carp×koi (RK) cross, using a virus challenge test. The infected fish had clinical signs that included gill necrosis and skin lesions. The RK and KR were highly more resistant (cumulative mortality: RK; 6% and KR; 8%) to KHV infection than KK fish (cumulative mortality: 28%). KHV DNA was confirmed in the tissues of all dead fish in groups by use of polymerase chain reaction (PCR), and the presence of the KHV protein in kidney was confirmed by immunohistochemistry. Histological analysis showed severe gill lesions and fusion of the lamellae in KK fish, but less severe damage in RK fish. In immunohistochemistry analysis, the KHV protein localized in the cytoplasm of infected kidney cells of KK, but the cross groups had lower levels of KHV antigen. Our data indicate that the cross groups had increased resistance to KHV disease.

In this study, we sought to improve the productivity of Far Eastern catfish (Silurus asotus) and tropical eel (Anguilla bicolor), which are high-value fish species in the Republic of Korea, as well as that of associated crops by applying biofloc technology (BFT)-based aquaponics systems. The following three systems were used: the flow-through system (FTS), BFT, and BFT aquaponics system (BAPs). Caipira lettuce (Lactuca sativa) was utilized and hydroponics (HP) was implemented to compare crop productivity. After 42 days of treatment, the BAPs and BFT systems improved fish productivity, with weight gain rates of 134.47 ± 1.80% in BAPs-cat, 130.38 ± 0.95% in BFT, and 114.21 ± 6.62% in FTS for S. asotus, and 70.61 ± 3.26% in BAPs-eel, 62.37 ± 7.04% in BFT, and 47.83 ± 1.09% in FTS for A. bicolor. During the experiment, the total ammonia nitrogen and NO₂⁻-N concentrations were stable in all plots. In the case of NO₃⁻-N, BFT showed an increasing tendency while both BAPs showed a decrease compared with that of the BFT. BAPs-cat (total weight: 224.1 ± 6.37 g) and HP (220.3 ± 7.17 g) resulted in similar growth. However, in BAPs-eel was 187.7 ± 3.46 g due to root degradation. Water content analysis showed that BAPs-cat and BAPs-eel contained sufficient K, Ca, P, and S, which are important for crop growth. Overall, the effect of BAPs on fish growth was higher than that of FTS. This study reveals that integrating BFT with aquaponics improves productivity for high-value fish and associated crops while maintaining stable water quality. This method offers sustainable, efficient production, reduces environmental impact, and provides insights for future research in sustainable aquaculture practices.

Sustainable aquaculture requires innovative systems that enhance production efficiency while minimizing environmental impact. Among emerging technologies, biofloc technology (BFT) and recirculating aquaculture Systems (RAS) are widely adopted for intensive fish culture; however, their integration with aquaponics remains underexplored. This study aimed to compare the growth performance and water quality in aquaponic (AP) systems combining Japanese eel (A. japonica) and caipira lettuce (L. sativa) using BFT and RAS technologies for 28 days. This study compared four aquaculture configurations: BFT, RAS, BFT-AP (BFT with aquaponics), RAS-AP (RAS with aquaponics). Results showed that aquaponics integration seems to be improve the fish growth and apparent feed efficiency. Eels reared in BFT-AP achieved the highest final weight, weight gain, specific growth rate and apparent feed efficiency, which were relatively greater than in BFT, RAS, or RAS-AP systems. The growth of caipira lettuce was markedly enhanced in BFT-AP, with total biomass nearly four times that of RAS-AP. Electrical conductivity and total dissolved solids were relatively higher in BFT-AP than in RAS-AP, indicating nutrient enrichment beneficial for plants. In conclusion, integrating aquaponics with BFT substantially enhanced both eel and production of caipira lettuce. The BFT-AP configuration represents a more efficient and ecologically balanced model for sustainable aquaculture intensification compared with traditional RASs.