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Abstract:To elucidate the dynamics of fishery resources structure in the Yellow Sea and East China Sea, species composition, dominate species, spatial distribution of catch, community diversity and community structure of fishery species in the Yellow Sea and East China Sea were studied based on the bottom trawl survey data collected from June and September in 2013. A total of 185 fishery species were collected, including 93 dermersal fish species, 31 pelagic species, 48 crustacean species, 12 cephalopod species and one mollusk species. Among these fish species, the richest species was found in Perciformes (27 families, 47 genera and 56 species). There was no obvious seasonal variation of dominate species. In summer, the dominate species were sand shrimp Crangon affinis and hairtail Trichiurus lepturus, whereas in autumn, the dominate species were the swimming crab Portunus trituberculatus, yellow small croaker Larimichthys polyactis, Japanese anchovy Engraulis japonicus and hairtail Trichiurus lepturus. The average catch per haul was higher in autumn (46.60 kg/h) than that in summer (39.35 kg/h). The spatial distribution of fishery resource in autumn concentrated in the Yangtze River estuary and Lvsi fishing ground. The diversity indices of fishery species in summer were higher than that in autumn. The fishery biological communities could be divided into two groups based on the cluster analysis. The separation between two groups was primarily influenced by the temperature and discharge of Yangtze River.

Abstract:Marine environmental factors affect the survival, growth, and reproduction of fish, etc., which play an important role in controlling fish population distribution. In addition, variation of marine environmental factors influences the spatial distribution and aggregation of fish. Based on remote sensing (RS) technology and geographic information system (GIS), the relationship between the spatial distribution of wintering anchovy (Engraulis japonicas) and environmental factors are analyzed, and then generalized additive models (GAMs) were established to quantitatively investigate the effects of spatio-temporal and environmental factors on stock density, using data collected by bottom trawl surveys and RS in central and southern Yellow Sea during 2000~2015. The results showed that wintering anchovy was concentrated in certain ranges of sea surface temperature (SST), chlorophyll a (Chl-a) concentration, as well as temperature gradient (TGR). The final model accounted for 44.76% of the variance in anchovy stock density. The spatio-temporal factors (year, hour, longitude, latitude) all had significant effects (P<0.05) on stock density, and spatial factors had the greatest impacts, accounting for 35.4% of the variance. Environmental factors such as water depth, SST, and TGR all had significant impacts on stock density (P<0.05). However, Chl-a concentration did not have a significant effect on anchovy stock density. The distribution of Chl-a concentration represents certain hydrodynamic characteristics; therefore, Chl-a concentration was included in the final model. Wintering anchovy was most abundant where the SST was between 7℃ and 11℃. The effect of SST on stock density was positive for temperatures lower than 9.5℃, and then there was a negative effect at warmer temperatures. Stock density was high where Chl-a concentration was between 1.2 and 2.3 mg/m3 and where TGR was from about 0.7℃ to 2.5℃; however, there were slight changes between the abundant ranges. The results of this study have important implications for fisheries management under marine environment dynamic scenarios in the Yellow Sea.

Abstract:To explore the seasonal variations in the phytoplankton community structure and their relationship with environmental factors in the offshore area of Laoshan, we designed 15 monitoring stations and made six investigative voyages in the spring, summer, and autumn during 2016~2017 while monitoring other environmental factors simultaneously. We detected 69 species belonging to 31 genera and two phyla of phytoplankton, most of which belong to temperate coastal species. Diatoma was the dominant phylum comprising 25 genera and 60 species, and dinoflagellates comprised 6 genera and 9 species. The seasonal variations in the dominant species were obvious. The most dominant species were Coscinodiscus oculus-iridis, Coscinodiscus asteromphalus, and Ceratium fusus. The total number of phytoplankton ranged from 732.10×104 to 1142.19×104 cell/m3, with an average of 937.15×104 cell/m3. The number of phytoplankton cells changed significantly during the year. The highest peak in 2016 appeared in autumn and the second highest peak in summer; the highest peak in 2017 appeared in summer and the second highest peak in autumn. The spatial distribution showed a decreasing trend from north to south, and the high-value areas appeared in Wanggezhuang Bay, Nanyao River, and Shilaoren Beach. The diversity and abundance of phytoplankton in the surveyed area are at a high level, and the phytoplankton community structure in this area is relatively stable, indicated by the analysis of the phytoplankton community structure index. The result of cluster analysis showed that the interannual variations in phytoplankton cell abundance are unobvious in spring, and the similarity is approximately 70% both in 2016 and 2017. However, the interannual variations in phytoplankton cell abundance are relatively obvious in summer and autumn, and the similarity is only approximately 40%, which is mainly related to environmental factors. The correlation analysis between phytoplankton community structure and environmental factors showed that the correlation coefficient between cell abundance average and COD is the highest (0.536) and the two factors that were most related to environmental factors were pH and COD, COD and DIN, and DO and COD. Therefore, the key limiting factors for phytoplankton cell abundance in the offshore area of Laoshan are COD, pH, DIN, and DO.

Abstract:Surveys have been conducted to investigate the spatial and temporal distribution of size-fractionated phytoplankton and other environmental variables in Sanggou Bay in four seasons for the period covering April 2017 until January 2018. Results showed that chlorophyll a concentration in the surface and bottom layers ranged from 0.74 to 3.27 µg/L and from 0.81 to 3.66 µg/L, respectively, with average values of (1.90±1.28) and (2.01±1.29) µg/L, respectively. There were significant differences in chlorophyll a concentration (P<0.01) and spatial distribution between seasons. In spring, microphytoplankton was the most abundant, accounting for 54.05% and 58.08% of the total phytoplankton in the surface and bottom layers, respectively. In summer, picophytoplankton was the most abundant, accounting for 24.46% and 20.70% of total cholorophyll a in the surface and bottom layers, respectively. In autumn, picophytoplankton accounted for 35.88% and 40.77% of total chlorophyll a in the surface and bottom layers, respectively. The contribution of picophytoplankton was low in winter and spring but increased significantly in summer and autumn. Redundancy analysis (RDA) results show that temperature is the main environmental factor affecting the size structure of phytoplankton. Dissolved oxygen had a significant effect on the percentage of picophytoplankton to total phytoplankton. The percentage of nanophytoplankton correlated with NO2 and NH4. There was a significant positive correlation between temperature and the percentage of microphytoplankton. This study provides basic knowledge for understanding the size structure of phytoplankton and estimating the carrying capacity of filter-feeding shellfish in the aquaculture ecosystem in Sanggou Bay.

Abstract:With the expansion of aquaculture, there is an increasing concern regarding issues such as conflicts with multi-sea use, low productivity, and higher economic costs. The selection of suitable sites for aquaculture is essential for utilization of sea space and improvement of the efficiency and profits of aquaculture industry. Kelp (Saccharina japonica) is the main culture species in Sanggou Bay and the surrounding waters. The assessment of suitability for kelp culture has been conducted with factors, including light intensity, water temperature, velocity, dissolved inorganic nitrogen, salinity, and depth. The remote sensing is employed to obtain the information of the existing culture areas. The environment variables were collected from field surveys along with model simulations. The Dynamic Energy Budget (DEB) model–STELLA model coupled with analytic hierarchy process was applied to calculate weighted-sums of scores for suitability evaluation. The result showed that the suitability scores were 0~6.7 with the main distribution range of 4~6. 23% of area was estimated to be the most suitable for kelp culture, whereas 10% of total study area was not suitable. The high score areas are mainly located in Ailian Bay and Chudao eastern surrounding waters, whereas the low score areas are mainly located in the shallow waters near the shore. The results have provided a guideline to help in site selection and in the management of kelp culture.

Abstract:Accurate knowledge of species distribution and population dynamics is the basis of conservation biology. However, for certain species that have a special life history and very few populations, species distribution detection becomes extremely difficult. The combination of DNA barcode technology and environmental DNA (eDNA) has solved these difficulties. Currently, this method has been applied successfully to biological testing, biodiversity assessment, biomass assessment, fish migration, and other research. Given the ease of degradation of eDNA and its low level in the environment, exploring its persistence in the environment is critical for accurate qualitative and quantitative analysis. In this study, Fenneropenaeus chinensis was used as the research subject. The degradation of eDNA in a water environment was quantitatively analyzed by real-time fluorescent quantitative PCR. The relationship between eDNA degradation rate and time was explored. The most suitable eDNA was selected based on Akaike Information Criterion (AIC). A statistical model of degradation of eDNA over time was used. The experimental results showed that the level of eDNA in water is negatively correlated with time. After the source of eDNA was removed, its residence time in the environment was about one month. The aim of this research was to provide a theoretical basis for the qualitative detection and quantitative assessment of rationally planned species, with a view to minimizing experimental error caused by human factors.

Abstract:To explore the community structure of epiphytic bacteria on the sporophytes and gametophytes of kelp Saccharina japonica, sequences of 16S rRNA of epiphytic bacteria found on the mature leafy sporophytes (S1), filamentous gametophytes (S2), sporelings (S3), and big leafy sporophytes (S4) were analyzed using Illumina sequencing technology. The results showed that 23 phyla, 156 genera, and 244 kinds of OTUs (Operational Taxonomic Units) were identified in these samples. At the phylum level, Proteobacteria showed higher abundance, with relative abundances of 53.0%, 94.3%, 77.2%, and 36.7% in S1, S2, S3, and S4 samples, respectively. Cyanobacteria showed higher abundance of 43.8% in S4 samples only. At the genus level, the relative abundances of Pseudoalteromonas in S2, S3, and S4 were 65.00%, 44.88%, and 25.57%, respectively, but only 0.18% in S1. The community structure of epiphytic bacteria varied greatly among samples. S1 and S4 samples were clustered together, but S2 and S3 samples were clustered in another branch. The species of the bacteria in S2 samples were single and unevenly distributed. S1, S3, and S4 samples were rich in bacteria, while the relative abundance between different bacteria in S4 samples varied greatly compared to that in other samples. This study revealed that there was an increasing trend in the abundance of alginic acid-degrading bacteria during the breeding stage of S. japonica (S2, and S3), and there was a high abundance of symbiotic Cyanobacteria in the big leafy sporophyte stage (S4).

Abstract:The simultaneous removal of ammonia and nitrate nitrogen is a challenging process in the treatment of recirculating aquaculture systems. This study first analyzed the effects of current density, plate area ratio, plate spacing, and initial pH on the removal rates of ammonia and nitrate nitrogen by a single-factor experiment. To understand the effects of different influencing factors on the efficiency of nitrogen removal, four-factor and three-level response surface experiments were designed on the basis of the central combination principle of Box-Behnken in Design-Expert software. Subsequently, the reaction conditions for the simultaneous removal of ammonia and nitrate nitrogen were optimized using a response surface model. Finally, the optimized reaction conditions were evaluated using verification experiments. In the single-factor experiments, we found that the changes in the current density, plate area ratio, plate spacing, and initial pH had little effect on ammonia and nitrate nitrogen removal. The removal rate of ammonia is always > 80% in the given reaction conditions, whereas the changes in reaction conditions significantly affected the removal rate of nitrate nitrogen, which ranges from 29.8% to 80.9%. The constructed response surface model showed that the regression coefficient (R2) was 0.9340 and the correction coefficient (R2) was 0.8681, which showed that the model has good accuracy. We obtained the optimal reaction conditions using the response surface model: current density was 25.6 mA/cm2, plate area ratio between cathode and anode was 1.6:1, plate spacing was 2.5 cm, and initial pH was 6.6. Experimental verification under the reaction conditions proved that the removal rate of nitrate nitrogen could reach up to 81.5% and the removal rate of ammonia up to 87.3%. This experiment showed that electrochemical treatment can effectively achieve the simultaneous removal of ammonia and nitrate nitrogen and that application of the response surface model can improve the nitrogen removal efficiency of electrochemical treatment in aquaculture wastewater.

Abstract:In order to explore the genetic structure of sea cucumber populations with different body color characteristics in different sea areas, 16S rDNA, COⅠ and D-loop gene sequences of eight populations of sea cucumber (Apostichopus japonicus) from China, Korea and Russia were amplified by PCR. Genetic diversity and evolutionary relationship of the 8 populations were analyzed by 16S rDNA, COⅠ and D-loop gene sequences from 80 samples. The results showed that the sequence lengths of 16S rDNA, COⅠ and D-loop genes were 543 bp, 656 bp and 509~527 bp, respectively. There were 16 polymorphic loci and 16 haplotypes in the 16S rDNA sequence, the haplotype diversity index was 0.629, the nucleotide diversity index was 0.0016, and the average nucleotide diversity was 0.880. A total of 62 polymorphic loci and 38 haplotypes were detected in the COⅠ sequence, the haplotype diversity index was 0.958, the nucleotide diversity index was 0.0073, and the average nucleotide diversity was 4.796. A total of 200 polymorphic loci and 61 haplotypes were detected in the D-loop sequence. The haplotype diversity index was 0.992, the nucleotide diversity index was 0.0157, and the average nucleotide diversity was 6.834. The results showed that the polymorphic loci, haplotypes and nucleotide diversity of D-loop and COⅠ sequences were significantly higher than those of 16S rDNA sequences, which were more suitable for the analysis of genetic structure in different populations of the same species. The genetic diversity of the three populations was the highest in the Posco area of South Korea, which may be related to the influence of ocean currents. The COⅠ gene was used to analyze the genetic differentiation of three body color sea cucumbers collected from Posco, the genetic differentiation coefficient Fst was less than 0.05, and there was no genetic differentiation. The results of phylogenetic tree construction using COⅠ gene showed that the Qingdao and Yantai sea cucumber population were clustered into one branch, then the Korean Mokpo black sea cucumber population clustered into one branch, from the inner outward are successively the Russian population and the Korea Posco population. The results showed that the populations with different body colors were poorly differentiated, and the genetic distances and clustering of different populations had the strongest correlation with their geographical distribution.

Abstract:In order to explore the molecular mechanism of high-temperature tolerance in turbot, Scophthalmus maximus L., and to screen heat tolerance related genes, the IlluminaHiSeq-2500 platform was used to sequence the transcriptome of five turbot kidneys from five different heat treatments, through bioinformatics analysis, including GO (gene function annotation), SSR (simple repeat sequence) analysis, etc. The main results obtained were as follows: the total number of Unigenes obtained by assembly was 68525, the length range was 201~23456 bp, the average length was 1124 bp, and the length of N50 was 2316 bp. Sequence alignment and function annotation of Unigenes was conducted in Nr, Swissprot, KEGG, KOG, and GO databases. A total of 25,498 clusters were obtained, of which the Nr database noted the most Unigenes; and according to GO function classification, had three kinds of cell components, molecular functions, and biological processes, including 56 functional groups. A large number of Unigenes were related to cell processes, metabolic processes, catalytic activities, biological regulation, and stress response. Further, Unigenes were classified into 218 metabolic pathways and five KEGG pathways: metabolic pathway, genetic information processing, cellular processes, environmental information, and biological systems. A total of 65 transcription factors were detected by transcription factor analysis, with the C2H2 Zn finger protein family having the highest number of genes. Through the analysis of gene expression profiles under different temperature stress, there were significant differences among different temperature groups, In the 20℃ and 28℃ groups, the difference was the largest; 4734 genes, of which 3386 were up-regulated and 1348 were down-regulated. In this study, we established a database of renal transcriptional groups in turbot under heat stress, which provides abundant data for the study of molecular mechanisms of heat stress in turbot.

Abstract:The effects of two factors (temperature and diet) on the gonadal development and quality of the resulting offspring of sea cucumber (Apostichopus japonicus) were examined in this study. Two temperatures (12℃ and 15℃) and three diets (50% Sargassum thunbergii Kuntze powder + 50% sea mud, 50% Laminaria japonica powder + 50% sea mud, and 25% S. thunbergii Kuntze powder + 25% L. japonica powder + 50% sea mud) were tested through single factor experiments. In addition, changes in the biochemical composition of the body wall during conditioning and biochemical composition of the female gonad after conditioning in different treatments were also quantified. Sea cucumbers were maintained in seawater, which was changed daily and provided with aeration, and were fed at a daily ration equivalent to 5%~10% of their dry biomass. Three replicate tanks were assayed for each treatment. Gonad index and spawning rate of female animals, egg diameter, fertilization rate of eggs, hatching rate of larvae, and body length of early auricularia were also evaluated. The results of the temperature treatments revealed that spawning rate, gonad index, and fecundity of females were significantly affected by temperature, and significantly higher at 15℃ than that at 12℃ (P<0.05). In the diet treatments, there were no significant differences in gonad index, spawning rate, and fecundity of females among the three groups; however, the mixed algae powder group showed the highest values. Hatching rate of embryos and body length of early larvae in the mixed algae powder group were significantly greater than that in the L. japonica powder group. The results indicated that egg quality was the best in a broodstock supplied with mixed macroalgae powder and sea mud. Biochemical analysis of the body wall revealed that carbohydrate levels in the A. japonicus body wall declined during conditioning, supporting the theory that carbohydrates are mobilized to provide energy or precursors for lipid or protein synthesis in the gonad.

Abstract:To investigate the diet feeding rhythm of juvenile of Thamnaconus septentrionalis and gastric emptying model, a once-per-day satiation feeding treatment (one day was divided into eight time periods, each time period was used as one treatment, and the fish of each treatment were fed to apparent satiation once a day) and a continuous feeding treatment with fixed intervals (one day was divided into eight time periods, the fish in each tank were fed to apparent satiation, eight times a day) were conducted for 7 days. The experimental fish [(4.28±0.46) g] were removed at various intervals (0, 2, 4, 6, 8, 10, 12, 14, 16, 20, 24, and 28 h) after satiation feeding. The wet mass of the chyme was determined and the applicability of the three mathematical models (linear model, exponential model, and square root model) was compared by the fitness of gastric evacuation data in juvenile T. septentrionalis. The results showed that T. septentrionalis exhibit a 24 h diet feeding cycle under two feeding scenarios. The feeding rate under the segmental continuous feeding mode was not significantly different at 03:00, 06:00, 09:00, and 12:00, but decreased rapidly after reaching a peak at 15:00 (P<0.05), and at 0: 00 reached the lowest value (P<0.05). The feed efficiency was not significantly different at 03:00, 06:00, 15:00, and 18:00 in the once-per-day satiation feeding, and the specific growth rate was significantly higher than that of a once-per-day satiation feeding (P<0.05). (2) The feeding rate of experimental fish decreased rapidly after 18:00 in the continuous feeding with a fixed interval (P<0.05), and reached the lowest value at 00:00 (P<0.05). The specific growth rate and feed efficiency at 09:00 and 12:00 in the experimental fish were significantly higher than at the other times of the day (P<0.05), optimal feeding times in T. septentrionalis culturing were during 15:00~18:00. (3) Among the three models, the gastric emptying rate was best fitted the square root model, and the equation was y0.5=2.802‒0.204t (R2=0.987). According to the square root model, the feed in the stomach was fed for 10 h. The left and right sides were completely emptied to the level before feeding, and the 80% gastric emptying time was 6 h. Based on the above indicators, it is recommended to feed the T. septentrionalis 3 times every day during the production practice from 09:00 to 15:00, with an interval of 3 h.

Abstract:To explore the histological features of Lateolabrax maculatus juveniles cultured at different salinities, the structures of the gills, spleen, and muscle were analyzed at different salinities (0, 10, 15, 20, and 30) via histological analysis. The results showed that at salinity 0, the gill filaments of L. maculatus juveniles were closely arranged, the top of the gills expanded into a rod shape, and the gill cells were plump with more chlorine-secreting cells; the breadth of the gill filaments decreased, and the intervals of the gill lamella became larger as the salinity increased (P<0.05). At salinity 20, some gill lamellas decomposed and fell off, the number of chlorine-secreting cells on the gill filaments increased significantly. At salinity 30, the number and size of chloride cells increased as the salinity increased and some chloride cells expanded and dissolved. In freshwater, more blood cells and fewer lymphocytes were observed in the spleen, whereas in the hyposaline environment (salinity 10 and 15), the lymphocytes were enlarged and the number of melanin macrophages increased. At high salinity (30), the spleen cells and some lymphocytes showed swelling and vacuolation and were loosely arranged. At salinity 0, the muscle fibers of the juveniles were loosely arranged, polygonal or oblong, with larger major and minor diameters and smaller densities. With the increasing salinity, both the major and minor diameters of muscle fibers tended to decrease first and then increase again. At salinity 15, the short diameter of muscle fibers decreased and their densities increased, which were significantly different from that observed at salinity 0 and 10. At salinity 30, the long diameter of muscle fibers increased and their densities decreased. In summary, as the salinity increased, both the long and short diameters of muscle fibers tended to decrease first and then increase (P<0.05). The results indicated that the histological structures of the gill, spleen, and muscle of L. maculatus juveniles were affected by the environment and salinity.

Abstract:The aim of this study to establish and optimize an isolation and culture system for Sertoli cells of Nile tilapia. Fresh testis tissues from Nile tilapia in development stage Ⅲ were obtained and then rinsed with phosphate-buffered saline. The tissue was dissected into segments and digested with 0.5 mg/ml collagen for 30 min, followed by 0.25% trypsin–0.04% EDTA for 5 min, and the digestion was terminated with L-15 culture medium with 10% newborn bovine serum (NBS). Sertoli cells were selected using the characteristic that they adhered more quickly than germ cells to the culture vessels. Sertoli cells were cultured in 96-well plates in L-15, M199, or F12 culture medium, supplemented with 10% NBS, or L-15 culture medium supplemented with 5%, 10%, and 15% NBS, or L-15 culture medium supplemented with 10% NBS and 1% Nile tilapia serum. For each treatment group, Sertoli cells were collected from six culture wells every 2 days; the number of cells in each well was counted using a hemocytometer, and a growth curve was drawn for the Sertoli cells. Compared with F12 or M199 culture medium, more rapid growth of Sertoli cells occurred in the L-15 culture medium (P<0.01). Compared with supplementation with 5% or 15% NBS, the proliferation of Sertoli cells was accelerated (P<0.05) by supplementation with 10% NBS in the culture medium. Comparatively, the effect of the addition of 1% Nile tilapia serum was greater (P<0.05) than the absence of serum. The proliferation of Nile tilapia Sertoli cells can be improved by supplementation with 10% NBS and 1% Nile tilapia serum in L-15 cell culture medium.

Abstract:In this study, based on the transcriptome of Exopalaemon carinicauda under hunger stress, SHMT genes were obtained by rapid amplification of cDNA ends (RACE) (GenBank accession No: MH013225). The full-length cDNA of the SHMT gene was 1855 nucleotides and contained an open reading frame (ORF) of 1407 bp, encoding a protein of 468 amino acid residues, with the predicted molecular weight of 152.55 kDa, and theoretical isoelectric point of 4.90. Multiple sequence alignment and phylogenetic analysis indicated that E. carinicauda SHMT gene is most homologous (96%) with that of Eurytemora affinis. The expression pattern of SHMT gene in different tissues was analyzed by qRT-PCR. The results showed that SHMT gene was expressed in all tissues of E. carinicauda. Transcript levels were high in the heart and ovary and were significantly higher in the ovary than in the other tissues. The results of different concentrations of Cd2+ stress showed that the expression patterns of lower cadmium stress were basically the same, showing a trend of alternately first increasing and then decreasing. Under high concentration of Cd2+ stress, the expression level was extremely low; and not even detected in these tissues. This suggests that high concentration of Cd2+ stress can inhibit the expression of the SHMT gene. The specific mechanism needs further study.

Abstract:Caulerpa lentillifera is a seaweed species with increasing large-scale economic value due to its nutritional and health benefits. With the expansion of farming scale, problems associated with various diseases are becoming more common and severe. However, few research focusing on this topic have been published. In this study, the strain CL2017070801002 was isolated from C. lentillifera, which was diagnosed with black-brown disease in Dalian´s breeding farm. Following infection of healthy C. lentillifera with this strain at a concentration of 103~108 CFU/ml, each experimental group developed different black-brown lesions within 7 days. Under scanning electron microscopy, a large number of bacteria were accumulated on the cell surface of the alga, and the cells ruptured and died over time. These results indicated that CL201707070801002 was the causative pathogen of black-brown disease of C. lentillifera. Using gram staining as well as physiological and biochemical characteristics based on a 16S rDNA phylogenetic tree, the strain was identified as Vibrio alginolyticus. CL2017070801002 was highly sensitive to chloramphenicol, tetracycline, fleroxacin, doxycycline, and florfenicol; moderately sensitive to gentamicin and clarithromycin; and not sensitive to penicillin and cephalosporin. These results will provide useful information for the prevention and control of bacterial diseases of C. lentillifera.

Abstract:In this study, Caridina japonica eggs at different developmental stages were incubated in vitro within a self-made incubator. The goal was to provide a reference for research on C. japonica reproductive biology and crustacean embryo in vitro hatching technology. The results showed that C. japonica fertilized eggs took about 25 days to hatch into larvae at a water temperature of 25.5℃ and the developmental accumulated temperature reaches about 637.5℃. The embryonic development went through eight stages: Fertilized eggs, cleavage stage, blastula stage, gastrula stage, embryonized nauplius stage, embryonized metanauplius stage, embryonized protozoea stage, and embryonized zoea stage. The embryos at different developmental stages could hatch to zoea larvae and can develop normally. The maximum in vitro hatching rate was (80.7±2.4)% found in eggs at embryonized zoea stage, which was not significantly different from that observed in normal ovigerous females (79.1±4.9)%. The minimum in vitro hatching rate was (28.2±2.6)%, found in eggs at cleavage stage, which was significantly lower than that of normal ovigerous females. Water temperature had a marked effect on embryonic development using in vitro hatching method. Incubation time gradually decreased with increasing temperature at a range from 15.0℃ to 32.5℃, i.e., where (436.8±124.8) h at 15.0℃, (228.0±88.8) h at 32.5℃. However, the metamorphosis rate from ZⅠ to ZⅡ began to decline when water temperature exceeded 29.0℃.

Abstract:Light is an important environmental factor affecting the growth and development of aquatic animals, and its propagation characteristics in aquaculture waters are still unclear. In this experiment, five light emitting diode (LED) light sources were selected: red (peak at 645 nm), green (510 nm), blue (445 nm), UVA (355 nm), and full spectrum (the wavelength of white light emitted by blue light excited silicate phosphor can reach λ400~800 nm). The radiation irradiance was adjusted to 60 W/m2, and the propagation law of irradiance was studied under different breeding water quality environments to provide references in order to meet the photobiological requirements of indoor factory aquaculture and the standardization control of aquaculture environment. The experimental results showed that the transmittance of five different LED light sources decreases with the increase in water depth. The variation trends of different light sources were different. When the water depth was 10 cm, the green light showed the largest transmittance (46.01%±4.03%), whereas UVA showed the lowest value (26.01%±2.53%). When the water depth was 150 cm, the light transmittance of all five light sources was less than 1.5%. The attenuation curves of light transmittance in water of five different light colors all agree with power function. The absorption of LED lights by water was discrepant in different spectral regions and has obvious selectivity. Most of the infrared and ultraviolet parts of the spectrum were absorbed by water. The absorption of the red, yellow, and green spectra in the visible spectrum band is also significant. LED light is severely attenuated in aquaculture water, and water depth is the main factor affecting LED light propagation (P<0.01), followed by total suspended solids (TSS) and chemical oxygen demand (COD). However, the extent to which different light sources are affected by TSS and COD content in aquaculture water varies. The attenuation of light in water is caused by the absorption and scattering of light by water, and the attenuation rate of light in different wave bands is mainly determined by the absorption spectrum of aquatic media.

Abstract:Four LED spectral parameters were set, which were blue (λ450 nm), green (λ525 nm), yellow (λ590 nm), and white (λ400~780 nm), water temperature was controlled at (22±1)℃, photoperiod was 16L:8D. The light intensity was set at 200 mW/m2. The results showed that the fertilized eggs of Takifugu rubripes under the blue, green and yellow light hatched 2 days earlier than the white light. At the end of the experiment, the full length, body length, trunk length and tail length of the larvae under the blue light were the most. Under yellow light, the head length, eye diameter, and body height showed the fastest growth. For growth genes, the expression of growth hormone (GH) gene under the blue light was significantly higher than yellow and white light group (P<0.05), but there was no significant difference with green light group. There was no significant difference in gene expression for growth hormone receptor 1 (GHR1) and insulin-like growth factor type (IGF-1) under different spectra, but the expression of GH gene under blue light was the highest. The results showed that LED spectrum (blue, green, and yellow) promoted the hatching of the fertilized eggs of T. rubripes, and the blue spectrum is beneficial to the growth and development of the T. rubripes larvae. The paper provided a scientific reference for the incubation of T. rubripes.

Abstract:In this study, the effect of Vallisneria natans meal used as feed ingredient in the diet of grass carp (Ctenopharyngodon idellus) on growth, physiological, and biochemical properties was evaluated. Four isonitrogenous and isoenergic diets were formulated by replacing the secondary powder and rice bran with 0 (VN0, control), 10% (VN1), 20% (VN2), and 30% (VN3) V. natans meal. In addition, a group that was fed only with fresh V. natans was designed. Juvenile grass carp of initial weight (18.85±0.20) g were selected to be cultured for 56 days in indoor cement tank cages. The results showed that addition of V. natans meal did not affect the growth performance, survival rate of grass carp, and feed coefficient. With the increase in the amount of V. natans meal, the visceral index and hepatopancreas index significantly decreased, the activity of amylase in the foregut was significantly increased, and that in the middle and rear intestines was significantly decreased. In the control group, the protease activity of foregut, and middle and rear intestines, in turn, strengthened, and with the increase in the content of V. natans meal the activity of foregut protease was significantly increased; meanwhile, midgut proteinase activity increased first, then decreased, and increased again. The highest value was observed in group VN1, and protease activity in the posterior intestine showed a significant decrease trend. The superoxide dismutase (SOD) activity of the hepatopancreas was significantly increased, whereas malondialdehyde (MDA) content decreased first and then increased, and that in group VN3 was the highest. The content of serum total protein increased significantly, whereas the serum albumin content increased first and then decreased, and the highest value was found in group VN1. Compared with the control group, serum alanine aminotransferase (ALT) activity increased and then recovered to the control level, and serum aspartate aminotrasferase (AST) activity significantly decreased in V. natans meal groups, and there was no significant difference among the V. natans meal groups. The addition of V. natans meal resulted in significantly reduced apparent digestibility of the diets and enhanced resistance ability of grass carp to Aeromonas hydrophila to some extent. Group VN showed negative growth and depressed visceral index, hepatopancreas index, serum albumin, globulin, and ALT. The activity of amylase in the intestinal segments was significantly higher than that in all practical formulated diets. The activity of midgut protease in VN group was significantly higher than that in the control group, and that of hindgut protease was significantly lower than that of the control group. The above results showed that the addition of 10%~30% V. natans meal in the diet had no effect on the growth of grass carp, but was beneficial to the health of the fish body. The results indicated that V. natans meal used as the raw material of grass carp feed for resource utilization would be much better than fresh V. natans.

Abstract:In this work, changes in the quality and storage life of sturgeon fillets were compared during 3℃ partial freezing storage and 4℃ storage in order to develop a method that will improve the storage quality of sturgeon fillets. Several indicators including sensory evaluation, total visible colonies (TVC), pH value, volatile base nitrogen value (TVB-N), thiobarbituric acid (TBA), texture, volatile substances, moisture distribution state, and microstructure changes of muscle fibers were studied and were later used to evaluate the effect of two temperature storages on the quality of sturgeon fillets. The results showed that the proportion of free water and combined water, TVB-N, TBA, and TVC of sturgeon fillets stored at 4℃ and 3℃ increased with the extension of storage time, whereas texture indices such as hardness and springiness and the score of sensory evaluation showed a decreasing trend. Microstructure observations illustrated that stickiness appeared between the muscle fibers, and the sarcomere gradually became blurred with the extension of storage time, especially during the later period of 3℃ partial freezing storage. Interestingly, its chemical indicators including TVB-N and TBA did not exceed the hygienic limits, whereas sensory evaluation rates were unacceptable. Taking all these indicators into consideration, it was observed that the storage life of sturgeon fillet was 6 days at 4℃ and 18 days at 3℃. It can therefore be concluded that partial freezing temperature storage (3℃) maintained the quality of sturgeon fillets much longer compared with storage at 4℃. Microbes have a small effect on the decay process of sturgeon fillets, whereas ice crystal formation and endogenous cathepsin may be the main influencing factors that led to the destruction of its structure during 3℃ partial freezing storage. Results of this study will enrich the basic theory of aquatic products and provide a technique for sturgeon fillets storage.