Background: Scylla paramamosain is one of the commercially crucial marine crustaceans belonging to the genus Scylla, which is commonly distributed along the coasts of China, Vietnam, and Japan. Genomic and transcriptomic data are scarce for the mud crab. Light intensity is one of the ecological factors that affect S. paramamosain during indoor overwintering. To understand the energy metabolism mechanism adapted to light intensity, we analyzed the transcriptome of S. paramamosain hepatopancreas in response to different light intensities (0, 1.43, 40.31 μmol·m^− 2·s^− 1). Results: A total of 5052 differentially expressed genes were identified in low light group (LL group, 3104 genes were up-regulated and 1948 genes were down-regulated). A total of 7403 differentially expressed genes were identified in high light group (HL group, 5262 genes were up-regulated and 2141 genes were down-regulated). S. paramamosain adapts to different light intensity environments through the regulation of amino acids, fatty acids, carbon and energy metabolism. Different light intensities had a strong impact on the energy generation of S. paramamosain by influencing oxygen consumption rate, aerobic respiration, glycolysis/gluconeogenesis pathway, the citrate cycle (TCA cycle) and fatty acid degradation. Conclusion: Low light is more conducive to the survival of S. paramamosain, which needs to produce and consume relatively less energy to sustain physiological activities. In contrast, S. paramamosain produced more energy to adapt to the pressure of high light intensities. The findings of the study add to the knowledge of regulatory mechanisms related to S. paramamosain metabolism under different light intensities.

Light intensity is one of the ecological factors that appreciably affects the metabolism of Scylla paramamosain during overwintering. This study adopted the isobaric tag for relative and absolute quantitation (iTRAQ) method to investigate metabolic changes of S. paramamosain under three illumination levels (0, 1.43 and 40.31 μmol m-2·s-1) for four months during indoor overwintering. The iTRAQ identified 3282 proteins, among which 267 exhibited significant differential expression (122 upregulated and 145 downregulated) in the low light group, and 299 with significant differential expression (252 upregulated and 47 downregulated) in the high light group. Analysis of these results showed that there were different metabolic regulatory patterns under different light intensities. Low light is more conducive to the survival of S. paramamosain, which needs to produce and consume relatively less energy to sustain physiological activities. Thus, the essential proteins associated with physiological activities were significantly upregulated, while those related to energy production were significantly downregulated. In contrast, high light exerts a certain stress on the survival of S. paramamosain and required more energy to cope with this stress, which forced a significant upregulation of proteins related to stress response and energy production. The findings of this study highlighted the metabolic regulatory mechanisms of S. paramamosain under different light intensities.

As an experimental fish, juvenile Schizothorax wangchiachii were fed different dosages (100, 300, or 500 g), and the changes in water quality in the inlet and outlet of the biofilter and in the aquaculture buckets were measured under different circulation rates (1.5, 3, or 4.5 m ³ /h; water samples were collected every 2 hours). With 100 g of feed and different circulation rates (1.5, 3, or 4.5 m ³ /h), the average removal rates of ammonia nitrogen and nitroso nitrogen by the biofilter were 40.4, 36.8, and 27.7% and 43.9, 36.9, and 29.8%, respectively. With 300 g of feed, the average removal rates of ammonia nitrogen and nitroso nitrogen were 42.3, 37.9, and 33.6% and 45.8, 32.7, and 21.7%, respectively. With 500 g of feed, the average removal rates of ammonia nitrogen and nitroso nitrogen by biofilters with different circulation rates were 53.5, 42.6, and 35.7% and 40.3, 26.5, and 18.1%, respectively. Therefore, when the feeding amounts were 100, 300, and 500 g, respectively, the optimal circulation rates were 1.5, 1.5, or 4.5 m ³ /h, which allowed the best management and reduction in energy consumption of the circulating aquaculture system. This research conclusion provides a reliable scientific reference for the promotion of a low-cost new model of industrial circular water aquaculture.