Abstract:In order to understand the spatial and temporal variation of abundance of picoplankton, four seasonal cruises were carried out in Sanggou Bay, a typical large-scale mariculture bay in north China, in April, July, November, 2017 and January, 2018. We used flow cytometry to study the abundance of the main picoplankton (Synechococcus, picoeukaryotes and heterotrophic bacteria) and further analyzed the relationship between the abundance of those species and environmental parameters (such as temperature, nutrients, dissolved oxygen, etc.) Results showed that the average values of Synechococcus, picoeukaryotes and heterotrophic bacteria in the surface layer of Sanggou Bay was (2.93±2.29) ×10³cells/mL, (13.84±12.81) ×10³cells/mL and (1.03±0.28) ×10⁶cells/mL, respectively. There were significant differences in both abundance of picoplankton and spatial distribution between seasons. In spring, Synechococcuswas mainly distributed in the northwest, southwest and outside of Sanggou Bay; it was mainly distributed in outside of Sanggou Bay in summer and winter; in autumn, it mainly concentrated in the Northwest coast. Picoeukaryotes were concentrated in the western coastal area in four seasons, showing a decreasing trend from the inside to the outside of Sanggou Bay. There are two high-value areas of heterotrophic bacteria in outside and western coastal of Sanggou Bay in summer. In spring, autumn and winter, heterotrophic bacteria and picoeukaryotes had the same distribution trend, and it were concentrated in the western coastal area of Sanggou Bay. The correlation analysis between abundance of picoplankton and environmental factors showed that the abundance of three kinds of picoplankton had a significant positive correlation with chlorophyll-a, temperature and particulate organic matter, and was negatively correlated with dissolved oxygen. There was no significant correlation between Synechococcus and PO₄³⁻, NO₃⁻ and NO₂⁻. However, there was a significant positive correlation between picoeukaryotes and NO₃⁻ and NH₄⁺. The results provide data support for further understanding the structure and function of aquaculture ecosystem.

Abstract:The marine ranching is a new type of marine fishery production and the leisure marine ranching is an important component. This paper reviews the research and development status of the recreational sea-fishing marine ranching. On account of the shortage of adult fish replenishment in China’s recreational sea-fishing marine ranching, the concept of “spawning-larvae and juvenile fish-young fish-adult fish” is proposed as the protection chain, to build the conception and related technologies of the marine ranching mode of the whole life history of fishes. This can finish the fish life history in the same marine ranching area, and also can recover fish resources, and increase biodiversity. The new marine ranching mode plays a demonstration role for the development of recreational sea-fishing marine ranching. This new type of marine ranching is proposed based on the construction of recreational fishing marine ranching, but its concept is also applicable to the construction of conservation and resource-proliferation marine ranching with other concentrated biological species that can complete their entire life history or most of their life history.

Abstract:In order to clarify the food web structure of coral reef ecosystem in Daya Bay, carbon and nitrogen stable isotope technology was applied to analyze carbon and nitrogen stable isotope ratios of major biological samples in the coral reefs, calculate the nutritional levels of major consumers and draw a continuous nutritional spectrum to construct the nutritional structure of coral reef in Daya Bay. In this paper, the trophic levels of the main consumers were calculated and the continuous nutritional spectrum was drawn to construct the nutritional structure in the coral reef area. The results showed that the δ¹³C values ranged from ?23.22‰ to ?10.76‰ and δ¹⁵N values ranged from 4.32‰ to 15.82‰ of reef ecosystem food web in Daya Bay. The average δ¹³C and δ¹⁵N values were ?16.47‰±2.89‰ and 11.46‰±2.37‰, respectively. The carbon and nitrogen isotope ratios of potential food sources and consumers were significantly different. According to the calculation of δ¹⁵N value, the trophic levels of the main consumers ranged from 1.70 to 3.64 as a whole in the reef area of Daya Bay. The trophic levels of gastropods, bivalves and fishes ranged from 1.84 to 2.68, 1.70 to 2.49, and 2.45 to 3.64, respectively. There were no significant seasonal differences both in the carbon and nitrogen isotope ratios of macrobenthos. Six quantitative community indices of nutrient structure of macrobenthos were calculated using the SIBER model. The level of food source diversity (CR), trophic level (NR) and bio-ecological space utilization (SEAc) were the highest in spring; species aggregation density parameter (MNND) and species aggregation uniformity parameter (SDNND) were the highest in winter. The results showed that different sources of organic matter contributed differently to the coral reef food web in Daya Bay. Phytoplankton and algae were important primary producers and important carbon sources driving the food web. Some consumers fed on common bait organisms, and there was a phenomenon of niche overlap. The contribution of organic matter from different sources to the coral reef food web varied, and each consumer group had different nutritional positions. The average trophic level of cephalopods was the highest, followed by fish and bivalves, mainly related to their diet. The consumers in Daya Bay coral reef ecosystem showed a nutrient level distribution with less nutrient species at both ends and more in the middle. There was no significant seasonal difference in carbon and nitrogen stable isotopes of coral reef benthic communities in the Daya Bay, which could be related to the characteristics of coral reef ecosystems and the size of benthic animals. In general, benthos had relatively stable levels of nutrient diversity and food webs, among which, there were large differences in nutrient levels and fierce competition within the population in spring, and the highest nutritional redundancy in the community in winter.

Abstract:Oyster shell was used as alkalinity supplementary material to study the feasibility of supplementing alkalinity with oyster shell in biofloc technology-tilapia(GIFT Oreochromis niloticus)culture system. At the start-up stage, the feasibility of supplementing alkalinity with different oyster shell dosages of 0 g/L (control group, group A), 0.36 g/L (group B) and 0.72 g/L (group C) was evaluated. The results showed that the level of alkalinity, pH and calcium in group C were significantly higher than those in group A, but there was no significant difference between groups B and C, so the effect of supplement alkalinity with oyster shell is obvious. Based on the results of the start-up of biofloc system, the effects of supplementing alkalinity to tilapia culture system with two forms of oyster shell (shell powder, group E) and (shell, group F) were studied. There were no significant differences in water quality, digestive enzyme activity, immunity and bacterial community composition among the three groups. Oyster shell and shell powder had no significant negative effects on the growth of tilapia and could be applied to the biofloc aquaculture system, but there is no obvious effect of supplementing alkalinity with oyster shell in culture stage. The supplementation of alkalinity had nothing to do with forms of oyster shell. Under the current experimental conditions, oyster shell can not completely replace sodium bicarbonate in the biofloc aquaculture system, and the related technology needs to be further optimized.

Abstract:In order to improve the efficiency and reduce the cost of marine aquaculture circulating water treatment, the combined process of biological aerated filter and electrochemical oxidation was developed in this study. The removal efficiencies of ammonia and nitrite at different anode potentials, influent ammonia and nitrite concentration were investigated. The interaction between microorganisms and the anode was studied and the energy consumption of electrochemical reaction was analyzed. When the hydraulic detention time is 45 min, at the anode potential of 1.4 V, and the ammonia and nitrite concentration is respectively 4.5 and 1.3 mg/L, the removal rate of ammonia by biological-electrooxidation system reached 88.8%, which was 7.6% higher than that of the control group. The concentration of ammonia and nitrite in effluent is respectively 0.5 and 0.9 mg/L, the removal rate of COD is 88.2%, which was 19.4% higher than the control group. The average energy consumption of electrochemical reaction is 0.040 kWh/m³. Microbial growth on electrode surface can promote the anodic oxidation process. The results of microbial function prediction show that the proportion of nitrification function is 0.03% in the experimental group and 0.07% in the control group. In conclusion, the biological-electrooxidation method shows good performance of removing pollutants in the marine aquaculture circulating water and great potential for developing high efficient marine aquaculture recirculating water treatment.

Abstract:In order to study the effect of three heterotrophic nitrifying bacteria on water quality of tilapia pond with bottom aeration, 600 Oreochromis niloticus with initial body weight of (2.66±0.94) g were randomly divided into 20 ponds. Five treatments included control group 1 (with air stone), control group 2 (with bottom microporous aerator), Rhodococcus pyridinivorans (P1-2) group (with bottom microporous aerator), Alcaligenes faecalis (P3-1) group (with bottom microporous aerator), and Bacillus megaterium (P5-2) group (with bottom microporous aerator), and each group had four replicates. Heterotrophic nitrifying bacteria with a final concentration of 5 x 10⁵ CFU/mL were added into the ponds every week. Water quality, growth and antioxidative abilities of fish were determined. The concentration of total nitrogen in water of all groups showed a continuous increasing trend during the experiment, while the accumulation of all indexes in the experiment groups were always lower than that in the control groups. The effect of P5-2 on improving the water quality of O. niloticus pond was the best. The accumulation of total nitrogen in pond water of P5-2 group was lower than that of control group 1 and control group 2 during the whole experiment. The accumulation of total nitrogen in pond water of P3-1 group was always lower than that of control group 2 during the whole experiment. The accumulation of total nitrogen in pond water of the P1-2 group was significantly lower than that of control group 1 and control group 2 at the 8th and 10th weeks. The accumulation of ammonia nitrogen in pond water of P5-2, P3-1 and P1-2 groups was lower than that of control group 1 and control group 2 during the whole experiment. The accumulation of nitrite nitrogen content in pond water of P5-2 group was significantly lower than that of control group 2 at the 2nd, 6th and 8th weeks. Adding heterotrophic nitrifying bacteria in pond water improved the antioxidative abilities of O. niloticus. Compared with control group 1, total superoxide dismutase (SOD) activity in serum of tilapia in P3-1 and P5-2 groups increased by 12.10% and 8.05%, respectively. Compared with control group 2, SOD activity in serum of O. niloticus in P3-1 and P5-2 groups increased by 21.25% and 16.87%, respectively. Compared with the control group 1, total antioxidant capacity (T-AOC) activity in serum of O. niloticus in P1-2, P3-1 and P5-2 groups increased by 82.78%, 98.68% and 245.70% respectively. Compared with control group 2, T-AOC activity in serum of O. niloticus in P3-1 and P5-2 groups increased by 1.69% and 76.95%, respectively. The results showed that adding heterotrophic nitrifying bacteria into pond could effectively improve the water quality and the antioxidative abilities of O. niloticus, but had no effect on the growth of O. niloticus.

Abstract:In order to study the combined effects of water salinity and dietary fat content on the growth, fillet nutrient composition and quality of Nile tilapia (Oreochromis niloticus), we designed the following experiment. Three different salinities (0, 8, 16) were set to raise O. niloticus [initial weight (5.0±0.2) g]. And in each salinity-group, O. niloticus was fed with two lipid-content diets, medium and high lipid diet respectively (MFD, 6% and HFD, 12%). After 8 weeks of breeding, the fish were sampled, and the growth, serum biochemical parameters, muscle nutritional composition and fillet quality related parameters were assayed. The results showed that, among MFD groups, the fish in medium salinity group (salinity 8) showed the highest final weight (FW), carcass ratio (CR), mesenteric fat index (MFI) and contents of total protein, amino acids and lactate in the muscle, but decreased feed conversation ratio (FCR), viscerosomatic index (VSI), hepatosomatic index (HSI) and pH of muscle, compared with the control group (salinity 0) and high salinity group (salinity 16). And compared with the control group and middle salinity group, the fish in MFD-high salinity group showed increased FCR, condition factor (CF), VSI, HSI, whole fish lipid, hepatic triglyceride (TG) and serum glucose, lactate, TG and glutamic oxaloacetic transaminase (GOT), but reduced whole fish moisture, muscle moisture, whole fish ash, meat yield (MY) and centrifugal water loss. In HFD group, with the increase of salinity, FW, survival rate and MFI were gradually decreased, and FCR, VSI, HIS and CF were increased. In HFD group, the fish in medium salinity group showed reduced muscle total protein and amino acid content. HFD-high salinity cultured fish showed increased whole fish ash, hepatic TG, serum glucose, GOT, muscle total protein, muscle TG and PL content, and decreased whole body lipid, hepatic glycogen, MY, centrifugal water loss, pH. However, either in freshwater or saltwater, the fish fed with HFD showed higher fat accumulation and muscle lactic acid content, but lower survival rate and MY, compared with MFD. Particularly in saltwater, the HFD fed fish showed significantly higher fat accumulation and muscle lactic acid content, but lower survival rate, FCR and MY. These results showed that suitable salinity (e.g. 8) of aquaculture water environment can improve the growth and flesh quality of O. niloticus, but the combination of HFD and high water salinity had negative effect on growth and flesh quality of O. niloticus.

Abstract:In this study, the growth and physiological parameters were compared between tilapia (GIFT Oreochromis niloticus) cultured in a traditional pond and that in an in-pond raceway system (IPRS) for 120 days. For the traditional way, 5 ind./m² (stocking density 1, SD1) were reared, while 180 ind./m² (SD2) and 270 ind./m² (SD3) were cultured in an IPRS. The main objective of this study was to find the appropriate density of tilapia to be cultured in an IPRS. The results showed that after 120 days of culture, the body weight, specific growth rate and absolute growth rate of the SD2 fish were significantly higher than those of the SD1 and SD3 fish. The survival rate, coefficient of variation of weight and feed coefficient rate of SD2 and SD3 tilapia were lower than those of the SD1 tilapia. Compared with SD1 fish at 30 days, the relative expressions of serum cortisol, serum alanine aminotransferase, lysozymal aspartate aminotransferase and hepatic hsp70 mRNA were significantly increased in the SD2 fish.The levels of serum cortisol and glucose in the SD3 fish were significantly higher after 120 days of culture than those in the SD1 fish. Compared with SD1, the levels of SAA, LAA and hepatic hsp70 mRNA expressions of the SD2 fish were significantly higher after 60 and 90 days, while the level of triglyceride was significantly lower during the whole experimental period. The results implied that tilapia in the SD2 were stressed in the early stage of cultivation but gradually acclimated to the environment, while tilapia in the SD3 were stressed for a relatively longer time. Taken together, this study demonstrated that the appropriate stocking density of tilapia cultured in the IPRS might be 180 ind./m² or less in order to obtain a better growth performance than in the traditional culturing mode.

Abstract:To obtain the microbes efficiently degrading pollutants, a new bacterial strain was successfully isolated that has the ability to degrade chemical oxygen demand (COD) from sewage efficiently. According to physiological and biochemical characteristics, and 16S rDNA sequencing phylogenetic analysis, the isolated strain is identified as Bacillus subtilis and named B. subtilis H2. A phylogenetic tree was constructed by comparing the 16S rDNA of the isolated strain and found to have a homology of 98.8% with B. subtilis strain SCUT09. The isolate H2 was found to be highly tolerant to a wide range of temperature, pH, and salinity conditions, however, the optimal growth conditions were at 42 °C, 6.5, and 1, respectively. Further, to explore its application in aquaculture, we investigated the Ctenopharyngodon idella intestine that was administered intragastrically with the B. subtilis H2 for 7 d then challenged with the pathogen Aeromonas hydrophila to observe the intestinal tissue changes of C. idella. B. subtilis H2 showed significant protection against A. hydrophila in the intestinal tract of C. idella. Moreover, to further explore the mechanism of action of this strain, the whole genome of B. subtilis H2 was determined in this study. The genome-wide sequencing of the H2 isolate resulted in 4 111 243 bp with GC content of 43.46%, encoding 4 213 genes that accounted for 87.67% of the gene coding region, including 31 rRNA and 87 tRNA genes. Comparative genomics analysis revealed, there were 3 551 core genes shared by this strain with B. subtilis 168. These results indicated that the isolated Bacillus strain could play significant roles in the treatment of sewage and aquaculture water.

Abstract:Aeration flow rate is the crucial controlling factor for aerated push-flow recirculating aquaculture system. In order to explore the effects of aeration flow rates on fish growth and flesh quality, a 56-days experiment was conducted with self-designed indoor recirculating aquaculture system model at 3 aeration flow rates (0, 30 and 50 L/min, respectively), where the growth performance and flesh quality of tilapia (Oreochromis niloticus) were monitored. The results showed: ① the final body weight and specific growth rate of tilapia in the 30 L/min condition were (79.56±3.82) g and (2.81±0.54)%/d, while the specific growth rate was 11.07% and 8.49% higher than those in the 0 and the 50 L/min conditions. At the same time, the total protein and triglyceride concentrations in the 30 L/min condition were higher but the urea nitrogen concentration was lower, e.g., on the 56^th day, the TP concentrations were 57.43% and 10.43% higher than those in the 0 and 50 L/min conditions, as for TCHO concentration, the increments were 22.19% and 12.32%, respectively. However, the BUN concentration decreased by 39.02% and 37.50%. Furthermore, the glucose concentration was not significantly affected by the aeration flow rates, but the alanine aminotransferase and aspartate aminotransferase concentrations in the 50 L/min condition were higher than those in the other conditions; ② the hardness, springiness and chewiness of the fish in the 30 L/min condition were significantly higher than those in the 0 L/min condition on the 56^th day, e.g., the hardness was 27.10% and 15.85% higher than that in the 0 and 50 L/min conditions, as for the springiness and the chewiness, the increments were 9.10% and 3.54%, 42.25% and 24.06% respectively, but the resilience was slightly higher in the 50 L/min condition than that in the other groups. Through analysis of test results, the growth rate of O. niloticus was slow due to lack of water stimulation and dissolved oxygen concentration at the low aeration flow rate (0 L/min), while the consumption of nutrients of tilapia was accelerated at the high aeration flow rate (50 L/min), only at the moderate aeration rate flow (30 L/min), the tilapia attained better growth performance and flesh quality.

Abstract:Generally, pH in the ponds of Litopenaeus vannamei farming exhibits long term trend as well as diel variation. Understanding the effect of pH variation on survival of L. vannamei is critical for improving water quality management in commercial white shrimp farming. In the present study, two independent experiments each with single factor design were conducted to evaluate the effects of pH level and amplitude of pH diel variation on survival of L. vannamei. Meanwhile, the physiological mechanisms were analyzed. In experimental I, four pH levels (6.6, 7.6, 8.6 and 9.6) were evaluated, and the average pH level (8.2) observed in commercial ponds was used as control. In experimental II, three amplitude of pH diel variation (7.5?8.2, 7.5?9.5, 7.5?10.0) were evaluated, and the average amplitude of pH diel variation (7.5?8.7) observed in commercial ponds was used as control. The results showed that pH level can significantly affect survival of L. vannamei, hemolymph cell count, and activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), glutathionereductase (GR), catalase (CAT), phenoloxidase (PO) and inducible nitric oxide synthase (iNOS) in vivo. Mortality of L. vannamei significantly increased, while activities of SOD, GSH-Px, GR, CAT, PO and iNOS declined, when environmental pH climbed from 7.6 to 9.6. On the other hand, amplitude of diel pH variation can significantly affect survival of L. vannamei and activities of antioxidant enzymes (SOD, GSH-Px, GR and CAT), but did not result in significant change in glutathione content. Mortality of L. vannamei significantly increased, while activities of SOD, GSH-Px, GR and CAT decreased, when amplitude of diel pH variation was extended from 7.5?8.2 to 7.5?10.0. This study reveals that pH level and amplitude of diel pH variation are important environmental factors responsible for survival of L. vannamei, and stress induced by unsuitable pH should be the physiology mechanism since high mortality of L. vannamei was accompanied by the change in activities of SOD, GSH-Px, CAT and PO. According to the present study, it is recommended that proper pH control should be listed as an important content for environmental management in L. vannamei pond farming.

Abstract:In order to study the effect of Houttuynia cordata planting in ponds on the repair of liver damage of GIFT Oreochromis niloticus caused by Streptococcus agalactiae, H. cordata were planted in culture ponds with 0% (control group), 5%, 10% and 15% of the pond area, respectively. After 90 days of culture, GIFT O. niloticus were artificially challenged by S. agalactiae. The livers were collected at 0, 24, 48 and 72 hours post infection (hpi), and the liver biochemistry, antioxidant activity, histology and HSP 70 expression were studied. The results showed that the activities of ALT and AST in the control group were the highest at 48 and 72 hpi. The activity of ALT in each H. cordata planting group had no significant change before and after infection. At 72 hpi, the activity of AST in 10% group returned to the level before infection. The antioxidant index showed that planting H. cordata could slow down the decrease of T-AOC in liver caused by streptococcal infection. It helps to significantly elevate the activity of antioxidant enzymes in liver, such as SOD, GSH-Px, CAT and NOS, and increase the scavenging ability of free radicals. It also reduced the levels of lipid peroxidation products(MDA). Histopathology showed that the hepatic sinuses in the control group were obviously congested, the hepatic cord was disordered and the hepatocytes were steatosis at 48 hpi, while O. niloticus in all planting H. cordata groups showed only eosinophilia and slight dilatation of hepatic sinuses after infection. The results of quantitative PCR showed that the expression of HSP 70 in the liver of GIFT O. niloticus in each group increased significantly after infection, and the expression of HSP 70 in the control group was significantly higher than that in the H. cordata planting group at each time point after infection. The results showed that H. cordata planting markedly protected liver against subsequent S. agalactiae-induced oxidative and inflammatory injury via slowing the rise of ALT and AST, increasing activity of antioxidant enzymes. It effectively reduce the pathological damage caused by streptococcal infection. GIFT O. niloticus promoted the early repair and degradation of damaged protein through the high expression of HSP 70. Planting H. cordata has anti-inflammatory effect and improves the ability of fish to resist pathogenic bacteria.

Abstract:In order to improve the quality of grass carp (Ctenopharyngodon idella) flesh, C. idella cultured in a pond was treated by a micro-flow water system. The effects of treatment time (0, 1, 4, 7 and 10 d) on the nutrient composition, flavor and sensory quality of C. idella flesh were investigated. The results showed that micro-flow water treatment could significantly influence the nutrient composition, taste compounds, volatile odor compounds and sensory quality of C. idella flesh. With the prolonged micro-flow water treatment time, the content of fat and total sugar in the C. idella flesh decreased significantly, and the content of ash increased significantly, but the content of protein showed no significant difference. Taste and odor characteristics of C. idella flesh were obviously changed by micro-flow water treatment according to the results of electronic tongue (e-tongue) and electronic nose (e-nose). In addition, micro-flow water treatment significantly increased the content of IMP (inosine monophosphate), umami amino acids (Asp and Glu), sweet amino acids (Ser and Ala) and bitter amino acids (Leu and Ile) in C. idella flesh, but significantly decreased the content of total volatile base nitrogen (TVB-N) and docosahexaenoic acid (DHA). The odor score, taste score and color score of C. idella flesh at treated 4 d were significantly higher than those of C. idella samples treated at 0 d and 1 d, but had no significant difference with C. idella samples treated at 7 and 10 d. Short-term micro-flow water treatment can effectively improve the flesh quality of C. idella. The suitable treatment time is 4 days. The treated C. idella flesh not only has no fishy odor, but also has higher umami taste.