Water Quality In Aquaculture Systems Research Articles

Effect of water quality ununiformity on production of marine medaka

The large amount of organic impurities deposited at the bottom of an intensive aquaculture pond often leads to the deterioration of the surrounding environment, creating additional environmental stresses on the farmed fish and affecting its growth. This study investigated the effect of water quality ununiformity on growth, feeding behavior, and stress tolerance of marine medaka (Oryzias melastigma) through differences of residence time in different water quality areas in the same aquaculture system. Through the pre-test, the flow field distribution in the aquarium for cultured experiment was clarified, and the water body in the aquarium was divided into the central area (Ce) and the corner area (Co) according to the water quality difference in different flow fields. Then, seven residence time gradients were set in Co, which were 24 h, 14.4 h, 7.2 h, 4.8 h, 2.4 h, and 0 h, respectively. That was, they accounted for 100% (P100), 60% (P60), 30% (P30), 20% (P20), 10% (P10), and 0% (P0) of a whole day, respectively. The results showed that, all water quality indicators such as dissolved oxygen (DO), pH, nitrite (NO2−-N) and non-ionic ammonia (NH3−N) in Ce and Co were consistent with the requirements of the standard (GB11607–89) during the 28-day cultured experiment, but the water quality in Co was gradually worse than that in Ce, with the prolonging cultured period. In spite of increasing the body length and body weight of medaka in all treatments, their growth rates had significant differences among several treatments (P0 = P10 = P20 > P30 > P60 = P100). And the fish's growth, feeding efficiency, and stress resistance decreased with the increase of residence time in Co (P < 0.05). Through nonlinear regression analysis, it was predicted that the accumulation of residence time of marine medaka stayed in the coner area was >6.667 h, its feeding behavior would be affected, and the corresponding appetite and food intake, immunity to disease and growth rate would all decreased. Attaining uniformity of water quality in aquaculture system may help improve fish welfare and increase the sustainability of aquaculture.

Metagenomic insights into feasibility of agricultural wastes on optimizing water quality and natural bait by regulating microbial loop

Effective screening feed substitutes for improving water quality in aquaculture systems has become a trending research topic now. In this study, three typical organic agricultural wastes, including sugar cane bagasse (SC), coconut shell powder (CS), and corn cob powder (CC), were selected to evaluate their potential roles on the optimization of water quality and natural bait compared to aquafeeds. Fish feed resulted in the highest growth rate of fish but the worst water quality. Organic detritus addition markedly improved the water quality, especially soluble reactive phosphorus (SRP, decrease of 56–61%) and ammonium (decrease of 16% in SC, 47% in CC). Specially, SC induced core microbes to mediate nutrients transformation and recycling (N2-fixation, ammonification, nitrification, dissimilatory nitrate reduction to ammonia and organic nutrients decomposition), which facilitated the primary productivity based on their positive relationships. This further reduced the available nutrients (especially SRP) in the water and built a mutually beneficial microbial loop. In addition, SC addition increased the abundance of genes involved in amino acids biosynthesis pathways, photosynthesis, and carbon fixation. These results led to energy transfer to higher trophic levels. The addition of CC had a better effect than SC in terms of lower nitrogen levels and a higher fish growth rate (19% in CC, 5% in SC). However, low temperatures and carbon accumulation jointly drive the anaerobic decomposition, resulting in unhealthy microbial loops and low fish growth rates. In contrast to the direct consumption of fish feed, organic detritus can induce more natural bait to provide food for fish by regulating the microbial loop, as showed by the microbial community composition in the water and fish gut. To comprehensively assess water quality, natural bait, and fish growth and quality, certain organic detritus should be considered as an auxiliary material to partially replace feed for healthy and sustainable aquaculture systems.

Nitrogen removal characteristics of Pseudomonas stutzeri F11 and its application in grass carp culture

This study was designed to investigate the denitrification characteristics of Pseudomonas stutzeri F11 under different environmental conditions and to evaluate the effect of these characteristics on nitrogen removal and the water microbiome in an experimental grass carp aquaculture system. The results showed that the optimal growth conditions of strain F11 were (1) ammonia-nitrogen (N), nitrite-N, or nitrate-N as sole N source; (2) initial ammonia-N concentration of 10–30 mg N/l; (3), initial nitrite-N concentration of 200 mg N/l; (4) sodium citrate as carbon source; (5) rotation (r) speed of 200 r/min; a C:N ratio of between 2 and 10; (6) culture at 32–37 °C. The addition of P. stutzeri F11 to the experimental grass carp aquaculture system reduced the levels of ammonia-N, nitrite-N, and total N in the water over an extended range, but had no effect on nitrate-N level. Results of the 454 pyrosequencing analysis indicated that the structure of the microbial community in the aquaculture water changed significantly after the addition of P. stutzeri F11 preparations. The addition of P. stutzeri F11 to the aquaculture system also altered the microbiome metabolism in the water, especially the bacteria involved in nitrogen metabolism. These results suggest that the addition of P. stutzeri F11 to an experimental grass carp aquaculture system decrease nitrogen levels and alter the microbial community structure of the water; as such, this bacterial strain could be a potential candidate for the regulation of water quality in aquaculture systems.

Optimization of C/N ratios for nutrient removal in aquaculture system culturing African catfish, (Clarias gariepinus) utilizing Bioflocs Technology

Development of aquaculture industry is restricted due the undesirable environmental impact associated with the effluent discharge that is rich in inorganic nitrogenous compound and organic matters. This situation could be improved through the implementation of Bioflocs Technology (BFT). BFT can enhance the water quality in aquaculture system by introducing natural nutrient recycling characteristics with the induction of appropriate carbon/nitrogen (C/N) ratio. However, the natural condition of aquaculture system, which is rich in inorganic nitrogen, could not sustain BFT. Thus, additional carbon is required to obtain a suitable C/N ratio for effective formation of bioflocs complex. This study focused on the determination of optimum C/N ratio by varying the dosage of carbon introduced into the system. Five different C/N ratios (i.e. 10, 15, 20, 25, 30) were evaluated in treating the aquaculture system culturing Clarias gariepinus to an acceptable water quality. Bioflocs density and water quality parameters were monitored throughout the treatment period. The highest removal of ammonia was achieved at 98.7% with the formation of 92.5 mL L−1 of bioflocs concentration at an optimum C/N ratio of 15. The results show that the utilization of BFT can potentially provide a sustainable and low maintenance treatment of aquaculture system.