Three densities of the sex-reversed male Nile tilapia, Oreochromis niloticus (20, 25, 50 fish/m³) were cultivated in an integrated multi-trophic recirculating aquaculture system (IMRAS) that involves the ecological relationship between several living organisms, i.e., phytoplankton, zooplankton, and aquatic plants. The results indicated that, by providing proper interdependency between various species of living organisms, the concentrations of ammonia, nitrite, nitrate, and phosphate in the system were maintained below dangerous levels for Nile tilapia throughout the cultivation period. The highest wet weight productivity of Nile tilapia of 11 ± 1 kg was achieved at a fish density of 50 fish/m³. The aquatic plants in the treatment tank could effectively uptake the unwanted nitrogen (N) and phosphorus (P) compounds with the highest removal efficiencies of 9.52% and 11.4%, respectively. The uptake rates of nitrogen and phosphorus by aquatic plants could be ranked from high to low as: Egeria densa > Ceratophyllum demersum > Vallisneria spiralis and Vallisneria americana > Hygrophila difformis. The remaining N was further degraded through nitrification process, whereas the remaining P could well precipitate in the soil sediment in the treatment tank.

Background and Aim: Oxygen concentration is an essential water quality parameter for aquaculture systems. Recently, supersaturated dissolved oxygen (DO) has been widely used in aquaculture systems to prevent oxygen depletion; however, the long-term effects of supersaturated oxygen exposure on aquatic animals have not been studied. In this study, we examined the effects of supersaturated DO on the growth, survival, and gene expression of Pacific white shrimp (Litopenaeus vannamei). Materials and Methods: Specific pathogen-free shrimp with a body weight of 8.22 ± 0.03 g were randomly assigned to two groups with four replicates at a density of 15 shrimps per tank. Shrimp were cultivated in recirculating tanks containing 50 L of 15 ppt seawater in each replicate. Oxygen was supplied at 5 mg/L to the control tanks using an air microbubble generator and at 15 mg/L to the treatment tanks using a pure oxygen microbubble generator. Shrimp were fed commercial feed pellets containing 39% protein at 4% of their body weight per day for 30 days. Average daily growth (ADG) and feed conversion ratio (FCR) were determined on days 15 and 30. Shrimp molting was measured every day. Individual hemolymph samples were obtained and analyzed for total hemocyte count, differential hemocyte count, and expression of growth- and immune-related genes at the end of the experiment. Results: Long-term exposure to supersaturated DO significantly affected shrimp growth. After 30 days of supersaturated DO treatment, the final weight and ADG were 14.73 ± 0.16 g and 0.22 ± 0.04, respectively. Shrimp treated with normal aeration showed significantly lower weight (12.13 ± 0.13 g) and ADG (0.13 ± 0.00) compared with the control group. FCR was 1.55 ± 0.04 in the treatment group and 2.51 ± 0.09 in the control group. Notably, the shrimp molting count was 1.55- fold higher in the supersaturated DO treatment than in the supersaturated DO treatment. The expression of growth-related genes, such as alpha-amylase, cathepsin L, and chitotriosidase, was 1.40-, 1.48-, and 1.35-fold higher, respectively, after supersaturated DO treatment. Moreover, the treatment increased the expression of anti-lipopolysaccharide factor, crustin, penaeidin3, and heat shock protein 70 genes by 1.23-, 2.07-, 4.20-, and 679.04-fold, respectively, compared to the controls. Conclusion: Supersaturated DO increased growth and ADG production and decreased FCR. Furthermore, enhanced immune-related gene expression by supersaturated DO may improve shrimp health and reduce disease risk during cultivation. Keywords: gene expression, growth performance, molting, pacific white shrimp, supersaturated dissolved oxygen.

Glycogen and poly-3-hydroxybutyrate (PHB) are excellent biopolymer products from cyanobacteria. In this study, we demonstrate that nitrogen metabolism is positively influenced by the exogenous application of trehalose (Tre) in Arthrospira platensis under nitrogen-deprived (−N) conditions. Cells were cultivated photoautotrophically for 5 days under −N conditions, with or without the addition of exogenous Tre. The results revealed that biomass and chlorophyll-a content of A. platensis experienced enhancement with the addition of 0.003 M and 0.03 M Tre in the −N medium after one day, indicating relief from growth inhibition caused by nitrogen deprivation. The highest glycogen content (54.09 ± 1.6% (w/w) DW) was observed in cells grown for 2 days under the −N + 0.003 M Tre condition (p < 0.05), while the highest PHB content (15.2 ± 0.2% (w/w) DW) was observed in cells grown for 3 days under the −N + 0.03 M Tre condition (p < 0.05). The RT-PCR analysis showed a significant increase in glgA and phaC transcript levels, representing approximately 1.2- and 1.3-fold increases, respectively, in A. platensis grown under −N + 0.003 M Tre and −N + 0.03 M Tre conditions. This was accompanied by the induction of enzyme activities, including glycogen synthase and PHA synthase with maximal values of 89.15 and 0.68 µmol min⁻¹ mg⁻¹ protein, respectively. The chemical structure identification of glycogen and PHB from A. platensis was confirmed by FTIR and NMR analysis. This research represents the first study examining the performance of trehalose in promoting glycogen and PHB production in cyanobacteria under nitrogen-deprived conditions.

Aquaponic systems (APSs) are based upon the sustainable utilization of nitrogen and phosphorus from a recirculating aquaculture system (RAS) as the nutrient source for plant production. Since the proper management of nitrogen and suspended solids are important for nutrient utilization efficiency, their optimization was evaluated. The RAS integrated with filtration unit and nitrifying biofilter provided complete nitrification without solid accumulation. Under the optimal treatment condition for 16 d, the treated water was low in ammonia (0 mg-N/L) and high in nitrate (> 6 mg-N/L) concentrations, which was appropriate for use in the cultivation of lettuce (Lactuca sativa). The RAS was then incorporated with hydroponics at a 5:1 fish: plant weight ratio. Moreover, the simplified APS was compared with a typical APS system that incorporated filtration unit and nitrifying biofilter. The natural growth of nitrifying microorganisms in the simplified APS could perform complete nitrification after 20 d of operation giving low ammonia and nitrite concentrations. The nutrient removal efficiency of the simplified APS resembled the typical system. During the aquaponics, the hydroponic unit in the aquaculture system was sufficient to control the nutrient concentrations within the appropriate levels for fish cultivation, i.e. nitrate (< 20 mg-N/L) and phosphate (< 3 mg-P/L).

Biological filtration plays an important role in a sustainable recirculating aquaculture system. To provide the appropriate conditions for biofilter acclimation, the effects of the salinity and acclimation period on nitrogen removal and microbial diversity were evaluated. Nitrification rate (NR) of the shrimp tank biofilter increased during the first 4 weeks and decreased thereafter. The highest NR was found in the 5 PSU salinity tank at week 2, whereas in the other salinities (15 and 25 PSU) the highest NR was observed at week 4. Meanwhile, the denitrification rate (DNR) increased significantly on week 8 and the highest DNRs were obtained after switching from an aerobic to an anoxic condition with methanol supplement. Under this anoxic condition the biofilter acclimated in seawater had the highest DNR. Changes in the microbial community during immobilization were monitored using Illumina MiSeq DNA sequencing. Proteobacteria and Bacteriodetes were the most abundant phyla found in this study. For nitrifiers, Nitrosomonadaceae were found from the first week of acclimation, while only one operational taxonomic unit (OTU) of Nitrospiraceae was observed. Under the anoxic condition at the end of the shrimp culture, two OTUs of Nitrospiraceae were found in both the 15 and 25 PSU tanks.