Abstract:In this study we analyzed the long-term variation of CPUE (catch per unit fishing effort) of Fenneropenaeus chinensis, Portunus trituberculatus and their predators in the Laizhou Bay of China. We also investigated the density and distribution of their food organisms and predators. Data were collected from 6 surveys in 2011 and 2013 and from previous records. We found that the present CPUE of F. chinensis, P. trituberculatus and their predators all largely decreased. During the releasing period, the food rankings of phytoplankton and macrobenthic animals were Ⅴ (very rich) and Ⅳ (rich) respectively. The density of food organisms for F. chinensis was the highest in the Northeast of the Laizhou Bay in May and in the Middle East in June. The density of predators of F. chinensis was the highest in the Middle West in May and in the Southeast in June. In May and June the density of food organisms for P. trituberculatus was the highest in the Southwest and Northeast. The density of predators of P. trituberculatus was the highest in the Middle West in May and in the Northwest in June.

Abstract:In this study we evaluated the level and distribution of nutrients in the Bohai Sea based on the survey in the spring and winter of 2014. We found that compared to winter of 2014, the level of inorganic nitrogen was higher in the spring, and the average contents of NO2- -N and NH+4-N were 1.94 and 3.49 times higher in the spring respectively. However, the average content of PO43--P in spring was about 80% of that in winter. According to the seawater quality standard, in winter the inorganic nitrogen content was lower than the first-level seawater standard, and the active phosphate content was slightly higher than the standard; in spring the inorganic nitrogen content was lower than the standard, and the active phosphate content was lower too. In terms of horizontal distribution, the coast area had higher DIN but lower PO43--P than the central area. Due to the effects of runoff river estuary the isolines of DIN and PO43--P were dense in the Laizhou Bay. In winter of 2014 the N/P ratio was slightly lower than Redfield ratio, but in spring the former was higher than the latter and there was a relative lack of inorganic phosphorus. According to the potential eutrophication assessment model, the nutrition level was poor in both winter and spring of 2014. In winter the organic pollution index A value was 0.66 and the organic pollution level was 1, indicating good water quality. In spring the organic pollution index A value was 1.05 and the organic pollution grade was 2, which meant the water body started to be polluted.

Abstract:The growing reclamation projects in Tianjin have exerted impacts on the marine ecosystem. From 2003 to 2012 the fishery production in Tianjin underwent a continuous decline. The situation was the most severe in 2008, which coincided with the large-scale reclamation in 2007. In this study we performed indoor simulation experiment, and explored the impacts of reclamations on marine organism resources. The results were shown as below: (1) Scapharca subcrenata and Mactra veneriformis displayed a vertical migration after being buried. The larger body length, the stronger biological migration ability. The mortality increased along with the burial depth. (2) As for the acute toxicity of the suspended solution on Artemia nauplii, the 96 h LC50 was 271 mg/L and the safe concentration was 27.1 mg/L. Biohazards of suspension increased over the time. (3) Test on the acute toxicity of the suspension on two economic fish species suggested that susceptibility of the larvae was raised over the time. Water temperature also affected the tolerance of larvae to the toxic suspension. With water temperature rose the tolerance was gradually reduced. The tolerance to toxic suspension varied greatly between different species.

Abstract:Knowledge on fish retina structure and associated characteristics helps better understanding their feeding behaviors. In this study we studied the structure of retina and visual characteristics of fries of Turbot Scophthalmus maximus using paraffin sectioning method. The experimental water temperature was (20.5±2.0)℃ and the water salinity was 29±1. Healthy fries were fixed after certain periods of light or dark adaptation that included newly hatched, 2 d, 5 d, 10 d, 16 d, 20 d 23 d, 26 d, 30 d, 34 d, 39 d, 43 d and 50 d. We also measured the pigment index (PI) after the adaptation of retina, the thickness of outer nuclear layer, internal nuclear layer and ganglion cell layer of retina, and the amounts of cone cells (CC), ganglion cells (GC) and nuclei of the outer nuclear layer (ONN) on the retina cross section. It was observed that the pigment layer and cone cell layer appeared in the retina of 2 d larvae, which was the visual support for the first feeding. The retina of 5 d larvae showed no motion response. From 16 d larvae to 30 d juveniles, the difference in the retinal PIs after light and dark adaptation (the former subtracted by the latter) significantly increased (P<0.01), which indicated the motion response in retina. During the development there was reduction in the amounts of CC and GC in the retina (P<0.01), while there was an increase in the amounts of ONN, the ratio of ONN to CC, and the ratio of ONN to GC (P<0.01). The retinas of turbot fries possessed high visual acuity and low photosensitivity before metamorphosis, however the former dropped and the latter increased after metamorphosis. This adapted to the weak light stimulation when their lifestyle changed from planktonic to benthic. The photo sensing system of post-metamorphosis benthic turbot was deficiently developed.

Abstract:In this study we optimized the methods for preparing the chromosomes of fish in different sizes and analyzed the karyotypes of the chromosomes of hybrid F1 groupers (Epinephelus fuscoguttatus♀ × Epinephelus lanceolatus ♂). Juveniles of hybrid F1 groupers were pre-treated with small fish swimming method premised on the results of pre-experiments. Then we collected the fins of hybrid F1 groupers to extract the chromosomes using different drop processing methods. The morphology and karyotypes of the chromosomes were observed and analyzed under the microscopes. We obtained clear images of the chromosomes with selected measures and their mitotic indices were different. The hot air drying method generated higher-quality chromosomes than the cold air drying method. Moreover, the mitotic index after hot air drying treatment was 2.58%, which was significantly higher than the cold air drying method (0.83%). It was found that there were 44 telocentric chromosomes and 4 subtelocentric chromosomes in the diploid, and that the karyotypic formula was 2n=48, 4st+44t, and NF=52. The chromosome number and karyotype of the hybrid F1 groupers were similar to their fraternal parent, while the karyotype was great different from their maternal parent. These results demonstrated that the chromosome number of hybrid F1 groupers was the same as their parents’, and the karyotypes showed a typical pattern of the higher group of fish evolution taxonomy. Furthermore, we also compared the karyotypes of the related 25 species of groupers. Our study will provide scientific guidance for the germplasm identification, genetic resources protection and breeding of the groupers

Abstract:Sox genes are developmental regulators characterized by the presence of an HMG (high mobility group) DNA-binding domain, and they exist extensively in animal bodies in nature. Members of the Sox gene family have been shown to be conserved during evolution and play crucial roles in a wide variety of developmental processes, including growth and development, hemopoiesis, the development and formation of the nervous system, especially, sex determination and differentiation. Genome resources are growing faster and faster, and it provides a platform for the study gene families by scanning whole genomic sequences. We study Sox genes in Cynoglossus semilaevis by using bioinformatics analysis on the standard of whole genome. A total of 23 Sox genes were identified systematically from C. semilaevis and classified into 7 subfamilies which had not been reported yet. They are subfamily B1, B2, C, D, E, F and K, each of these groups may have distinct and specific functions. Sequence analysis of conserved domain of Sox genes in C. semilaevis shows that, all of members in the family contain 9 amino acid residues (RPMNAFMVW) as a highly conserved motif except CseSox32. On the other hand, the motif in Sox32 is identical in all specie as RPLNAF. Research on the highly conserved HMG box in C. semilaevis causes the discovery of these Sox genes, and phylogenetic analysis supports the classification of subfamily. To date, about 10 and 40 Sox genes have been identified in invertebrates and vertebrates separately. The phylogenetic analysis also suggests that the groups of Sox genes might be extended in the process of evolution. Subfamilies have got convergence between different species, and got otherness inside one of these species. Gene location results show that these 23 Sox genes were distributed randomly on 15 chromosomes, and we do not find gene cluster. The analysis of gene structure divides all of the Sox genes into two categories, evaluation on the basis of the exon numbers of the gene are less or more than two. The expression profiles of C. semilaevis Sox genes show a characteristic of different kinds of gonad and metamorphosis specific, and it indicated Sox genes may play key roles during sex determination, gonad differentiation and early development in C. semilaevis. To sum up the above, we enhance understanding of Sox genes in C. semilaevis with bioinformatics analysis, such as system evolution, gene structure, chromosomal location and gene expression patterns. Our results suggest that bioinformatics analysis may contribute to further functional verification of gene family and be good for genome resources mining and utilization.

Abstract:Bioflocs are heterogeneous mixtures of microorganisms and organic particles that regulate the accumulation of ammonia and nitrite and serve as a supplemental food source for fish. A 56-day feeding experiment was conducted to investigate the effects of bioflocs on the growth performance, the activity of digestive enzymes, and non-specific immunity of (37.75±0.62) g juvenile Megalobrama amblycephala in zero-water exchange culture tanks. Glucose at different concentrations were used as the carbon source in the water. A series of C/N ratios including 8 (CN8), 12 (CN12), 16 (CN16) and 20 (CN20) were presented in biofloc-based tanks under zero-water exchange condition. Three biofloc treatments and one control treatment were applied to a triplicate. It was found that at the end of the experiment the survival rates of all the groups were >90% without significant differences between groups. The growth performance indicators such as the final weight, the weight gain and the specific growth rate were significantly higher (P<0.05) in the CN16 and CN20 groups than in the control group. Moreover, the biofloc treatments significantly enhanced activities of protease and amylase in the intestine of fish (P<0.05), but these treatments did not alter the body composition. We also observed marked differences in the activities of superoxide dismutase, alkaline phosphatase and lysozyme of the fish liver between the biofloc treatment groups and the control group. These results suggested that bioflocs in the CN16 and CN20 groups could improve the growth performance and feed utilization of cultured juvenile M. amblycephala, probably through the enhanced intestinal digestive enzyme activity and the subsequent feed digestion and utilization.

Abstract:Most of magnesium (Mg) in fish is contained in the bone. Dietary magnesium has been reported to affect growth in several species, but the effect of dietary Mg on growth of seabass (Lateolabrax japonicus) is unknown. This study was conducted to investigate the effect of dietary Mg supplement on growth, feed efficiency, morphometry index, and Mg concentration in vertebrae, muscle and serum of seabass. Six experimental diets were formulated to contain graded levels of Mg by supplementing the basal diet with 186, 350, 542, 735, 950, and 1220 mg/kg Mg in the form of Mg sulphate (MgSO4·7H2O). Triplicate groups of juvenile seabass with an initial body weight of (28.0±2.5) g were fed to apparent satiation twice daily for 56 d with the waterborne Mg concentration of 1115 mg/L. The experiment was carried out in flowing-water tanks. Dietary Mg supplement did not improve the specific growth rate, survival rate and feed efficiency of seabass (P>0.05). The hepatosomatic index, viscerosomatic index, condition factor, Mg concentration in vertebrae, muscle and serum were not affected by dietary Mg supplementation(P>0.05). Also crude protein, crude lipid, moisture and ash contents in muscle were no significantly different (P>0.05). These indicates the Mg requirement of sea bass was met by fish fed the basal diet and waterborne Mg concentration. Therefore, it is no need to additional magnesium supplementation in feed

Abstract:Estuarine tapertail anchovy Coilia nasus has been a highly popular and commercially valuable anadromous species in China the texture of which is delicate. Recently age estimation by otolith of this fish has become a hotspot in ecological research, which largely depends on efficient pre-treatment methods that generate clearer annual rings in the otolith of C. nasus. In this study we compared the effectiveness of several pre-treatment methods. The results showed that the transverse plane was clearer than the sagittal plane through the core; however, the latter was more suitable in some special analysis (especially microchemistry). Etching with 5% EDTA produced a clearer surface than 1% HCl. Analysis on the rings in the sagittal planes after etching suggested that the morphological change in the otoliths was correlated with transition in the habitat during the lifetime. In conclusion, the transverse plane is suitable for determining the age, and the sagittal plane is optimal in microchemical analysis.

Abstract:In this study, fourteen markers were analyzed to assess the genetic diversity of four wild geographical populations of Liza haematocheila from the adjacent waters of Huludao, Qingdao, Lianyungang, and Zhoushan. The results showed that there was a certain degree of polymorphism in the four populations and the percentages of polymorphic loci were 92.86%, 92.87%, 100%, and 85.71% respectively. A total of 61 alleles were detected in the four populations, and the average number of alleles was between 3.786 and 4.000 for each population and the effective number of alleles was from 2.673 to 2.899. The average values of observed and expected heterozygosity ranged from 0.359 to 0.389 and from 0.503 to 0.561 respectively. The mean polymorphic information contents were from 0.465 to 0.513. These results suggested that there was a moderate genetic diversity among the four populations, however, the Kruskal-Wallis test (SPSS software) indicated no significant difference in the genetic diversity among the four populations (H=0.187, df=3, P=0.980). The majority of loci in each population were found to deviate from the Hardy-Weinberg equilibrium (P<0.05). Moreover the Huludao and Zhoushan populations were found to have two loci with heterozygote excess (Fis<0), while the other two populations had three loci with heterozygote excess. This was probably caused by recent bottleneck effect. The values of genetic differentiation coefficients and gene flow were 0.148 and 1.444 respectively, which suggested a medium level of genetic differentiation and a certain degree of gene flow between the four populations. The genetic similarity coefficients of the four populations ranged from 0.623 to 0.818 and the genetic distance was between 0.202 and 0.473 among the populations. The genetic distance was the nearest between Huludao and Qingdao, and was the farthest between Lianyungang and Zhoushan. These results could be related to the diffusion of the mullet larvae, the inshore coastal ecological environment, and the community structure. Cluster analysis with the UPGMA method showed that the four geographic populations could converge into one cluster according to their distribution from north to south.

Abstract:The American shad (Alosa sapidissima) is an economically and ecologically valuable anadromous species native to the Atlantic coast of North America, distributed from the St. Lawrence River in Canada to the St. Johns River in northern Florida. In the past few decades, American shad have been introduced as a candidate species into Chinese aquaculture because Chinese shad (Tenualosa reevesii) was endangered. Nowadays the farming scale and techniques for American shad have been greatly improved in China. However, little histological study has been done on the early development of A. sapidissima larvae, especially on the eye ontogeny. Here we employed the paraffin section and HE section methods in a histological observation of the eye ontogeny of A. sapidissima. The results showed that the optic vesicle was formed in 21 h 13 min after fertilization, and then developed into the optic cup in 26 h 23 min after fertilization. At 35 h 44min the undifferentiated retina and lens were visible. As the embryonic development continued, the cornea was formed in front of the retina, which consisted of single cuboidal epithelium. On Day after hatching (DAH) 2, the sclera composed of cartilage and outer fibrous layer became visible, followed by the appearance of choroid. On DAH 3 the iris was present, and the retina differentiated into ten layers including pigment epithelium, visual cell layer, outer limiting membrane, outer nuclear layer, outer plexiform layer, inner nuclear layer, inner plexiform layer, ganglion cell layer, nerve fibre layer and inter limiting membrane, and then the rod cells were clearly observed in the visual cell layer. On DAH 14, the cornea was well developed and differentiated into five layers that were stratified squamous epithelium, lamina elastic anterior, stroma layer, lamina elastic posterior and endothelium. On DAH 22, the choroid gland appeared. On DAH 26, the choroid completely differrntiated into three layers (argenteum layer, the choriocapillary layer and the pigment layer). In addition, the iris also underwent full differentiation and contained layers of endothelium, iris anterior, stroma, iris posterior and pigment. On DAH 45, the inner nuclear layer of renita developed into two layers of horizontal cells, and it was that moment when the development of the eye structure was complete.

Abstract:Monopterus albus were widely distributed in the freshwater in China except for the Northwest and Southwest Plateau. M. albus were artificially propagated and cultured in the middle and lower reaches of the Yangtze River. Currently the sources of parents of include the wild, the artificial culture, and artificial propagation. In this study we compared the fecundity of M. albus from different sources, and investigated their distribution, variation, and biological indexes of individual fecundity. We found that the absolute fecundities (F) of wild female, artificial cultured female and artificially propagated female were 181–729 eggs, 165–589 eggs, and 135–352 eggs respectively. The individual relative fecundities to weight (FW) of the three groups were 5.4–11.8 eggs/g, 3.5–9.3 eggs/g, and 4.96–8.55 eggs/g respectively. As for the individual relative fecundities to length (FL), the values were 5.8–17.2 eggs/mm, 4.85–15.00 eggs/mm, and 4.35–9.03 eggs/mm respectively. There were highly significant differences in FW and FL (P<0.01) between the three groups. Moreover, there were significant differences in F and FL, but not FW, between individuals with both different sources and body colors. F of all subjects and FL of the wild subjects were strongly correlated to the body weight and length. F, FL and FW of wild female M. albus were all higher than those of the artificial cultured and artificial propagated M. albus, and the former exhibited obvious advantage in fecundity. Our study will provide important guidance for the population construction and refined breeding of M. albus.

Abstract:In this study we employed the RACE method to sequence the full-length cDNA of p38 MAPK gene of Fenneropenaeus chinensis for the first time and named it as Fcp38. The full-length cDNA sequence contained 1563 bp, including a 122-bp 5'-UTR, a 343-bp 3'-UTR, and a 1098-bp open reading frame (ORF) that encoded 365 amino acid residues. The isoelectric point (pI) of this peptide was 5.68, and the molecular mass was 41.77 kDa. Homology analysis revealed that the amino acid sequence of Fcp38 was highly similar to the p38 MAPK sequences in other species. The sequence similarity reached 98% between F. chinensis and Litopenaeus vannamei and Marsupenaeus japonicus. Fcp38 had a conserved Thr-Gly-Tyr (TGY) motif, a substrate-binding site Ala-Thr-Arg-Trp (ATRW), and an ED (ERK docking) motif. This structure played a critical role in the interaction between p38 MAPK and other molecules. The phylogenetic analysis showed that p38 of F. chinensis was in the same branch with L. vannamei and M. japonicus. The expression of Fcp38 gene in different tissues was also analyzed with quantitative real-time PCR. The results showed that Fcp38 existed in all the tested tissues including the intestine, gill, stomach, heart, hepatopancreas, muscles and hemocytes, and the expression was the highest in muscles. Real-time PCR analysis showed that ammonia-N stress significantly up-regulated the expression of Fcp38 in the muscles, hemocytes, gill, heat, intestine and stomach, and that there was a spatiotemporal pattern for the expression of Fcp38. These results implied that Fcp38 might play an important role in the response to the environmental stresses

Abstract:The cytochrome P450 is an important group of multi-functional oxidases engaged in the metabolism of exogenous substances. In this study we investigated the effects of enrofloxacin on the expression of CYP2 and activity of APND enzyme in hepatopancreas of Litopenaeus vannamei. Real-time PCR analysis revealed that CYP2 in L. vannamei was expressed in all tested tissues, including hepatopancreas, gills, hemolymph, muscle, carapace, intestine, stomach, heart and eyestalk. The expression level was the highest in hepatopancreas, and the lowest in hemolymph. After oral administration of enrofloxacin at different concentrations including 15 mg/kg (low-dose group), 30 mg/kg (middle-dose group), and 60 mg/kg (high-dose group), the level of CYP2 transcript in hepatopancreas decreased significantly (P<0.05) especially at 9 h (P<0.01), however exceptions occurred at 1 h, 24 h, and 96 h. The activity of APND that indicated the activity of CYP2 was measured with ELIASA. The result showed that the activity of APND was lower in the experimental groups than in the control group. APND activity in the high-dose group was lower than that in the low-dose group. All three experimental groups, especially the high-dose group (P<0.01), showed a significant decrease in APND activity (P<0.05) after 9 h, but an exception occurred at 3 h. The enzyme activity in all experimental groups was reduced (P<0.01) and reached the minimum level at 12 h. Changes in both the enzyme activity and the expression level displayed the same pattern. These results indicated that the expression of CYP2 could be impacted by enrofloxacin. Therefore, when administrating drugs in combination, the cumulative effects should be carefully evaluated.

Abstract:Acute hepatopancreatic necrosis disease (AHPND) is caused by infection with Vibrio parahaemolyticus. In this study, five strains of V. parahaemolyticus were isolated from Litopenaeus vannamei with AHPND. The primer set AP2 targeting the plasmid harbored in AHPND-causing V. parahaemolyticus (VPAHPND) was used in the PCR amplification, and it was found that all five isolates carried the AHPND related plasmid. Mitomycin C was used to induce and screen the lysogenic phages in VPAHPND isolates. The growth curves showed that two isolates of V. parahaemolyticus, 20130629002S01 and 20130726001S01, contained lysogenic phages. Phage 1 and Phage 2 were released from 20130629002S01 and 20130726001S01 respectively after the induction with 0.5 μg/ml mitomycin C. Transmission electron microscopy revealed that Phage 1 had a tailed shape and Phage 2 had a spherical shape. The challenge test on Artimia nauplii suggested that the virulence was significantly different between the 5 strains of V. parahaemolyticus. The pathogenicity of two lysogenic phages-containing strains, 20130629002S01 and 20130726001S01, was significantly lower than that of phage-free 20130721001S02. Our study suggested that the presence of lysogenic phage might not necessarily correlate with the pathogenicity of the host bacterium V. parahaemolyticus.

Abstract:In recent years there have been a number of outbreaks of lethal shrimp diseases caused by viral and bacterial infections in many countries, which hinders the development of shrimp culture industry. To protect shrimp from diseases, a lot have been done to improve the shrimp germplasm against disease, the shrimp culture technology, as well as the aquaculture environment. One example is the bioflocs technology (BFT) that helps eliminate harmful nitrogen sources, reduce water exchange rate, and increase the feed utilization rate. Probiotics such as Bacillus sp. could also improve water quality in the shrimp culture pond. In this study, we isolated a strain named 2013042402 (Strain 02) from a shrimp pond. Strain 02 was identified as Bacillus sp. using 16S rDNA sequencing and gas chromatographic analysis of the whole cell fatty acids. To investigate the function of Strain 02 in bioflocs for the shrimp culture system, we added three groups into the culture system that were Strain 02(2.0×104 CFU/ml) combined with sucrose (70% of feed), strain 02 alone, and sucrose alone. Then we measured a series of physicochemical parameters of the culture system including temperature, salinity, dissolved oxygen, pH, floc volume, ammonia-N and nitrite-N. We also examined the growth rate and the survival rate of shrimps, and the compositions of dominant bacterial communities in the water body. We found that the Strain 02-sucrose combination significantly reduced the concentrations of ammonia-N and nitrite-N in the water and improved the survival rate and growth rate of shrimps. This suggested that Strain 02 added to the bioflocs could improve the aquaculture water quality, optimize the structure of bacterial communities, and inhibit the growth of vibrio, therefore elevate the survival rate and growth rate of shrimps. Our study implied that the bioflocs technology could be highly improved by the addition of probiotics.

Abstract:In this study we developed fluorescence SYBR Green I real-time quantitative PCR (qPCR) to detect shrimp microsporidian Enterocytozoon hepatopenaei (EHP). A pair of specific primers was designed according to the SSU rDNA sequences of shrimp EHP published in GenBank and the optimized annealing temperature was determined to be 60℃. The melting curve of amplified products exhibited only one specific peak. Between 8.3×101–8.3×108 copies/µl the test results were linearly correlated with the titers of EHP. The cycles of amplification threshold (Ct) and the logarithmic of the initial template quantity [log(Sq)] conformed to Ct = –3.369 log(Sq) + 39.364, of which the coefficient of association R2 was 0.992 and the amplification efficiency was 98.1%. This method had high sensitivity (8.3×101 copies/µl), and generated duplicable results both within a group and between different groups. The test of 31 samples of farmed L. vannamei suggested that the qPCR method was 4 times more sensitive than the previously reported nested PCR method. To further verify this method, we tested hepatopancreatic DNA (HpDNA) samples extracted from 94 samples of L. vannamei that were collected from farms in Jiangsu, Hainan, and Shandong provinces. The results showed that the EHP loads in the hepatopancreas were negatively correlated with the shrimp growth rates. EHP load above 103 copies/(ng HpDNA) indicated high risk. In conclusion, we developed a highly specific, sensitive, rapid and quantitative method, which could be a useful tool in the prevention and control of shrimp microsporidian E. hepatopenaei.

Abstract:White spot syndrome virus (WSSV) is the most important and harmful pathogen in shrimp farming. As the areas and scales of prawn farming expand, more and more genetic variation in different WSSV strains has been noticed. Three regions of the WSSV variation located in ORF75, ORF94 and ORF125 of the genome, containing various numbers of tandem repeats (VNTR), and VNTR has been widely used as genetic markers in epidemiological studies. In this study we studied the molecular epidemiology of variation characteristics of WSSV in different areas of China. Forty-eight PCR-proved WSSV-positive samples were collected from Liaoning, Hebei, Shandong, Jiangsu, Zhejiang, Fujian and Guangdong during the white spot disease outbreak periods from January 2014 to August 2014. These samples were genotyped by PCR with specific primers of ORF75, ORF94, and ORF125, and the amplified fragments were then connected to T-vector and transformed into E. coli Top10. After the sequencing, we assayed the three WSSV VNTR regions in ORF75, ORF94 and ORF125 from different samples. The results confirmed 5 ORF75 VNTR types consisting of 4, 10, 11, 12 and 13 repeat units (RUs). We also identified 2 ORF94 VNTR consisting of 4 and 14 RUs, and 5 ORF125 VNTR consisting of 0, 3, 5, 6, and 7 RUs. The results suggested that there was a certain degree of prevalence and variation in WSSV in most parts of China, and that the variation in ORF75, ORF94 and ORF125 between different strains was obvious. Moreover, there could be a correlation between the specific VNTR variation and the disease outbreaks in different regions, which needs further investigation.

Abstract:In this study we used static water method to investigate the effects of temperature and salinity on oxygen consumption rate and ammonia excretion rate of Cantharus cecillei with two different sizes. The results were described as following: (1) Temperature and body size alone had significant effects on oxygen consumption rate (OR) and ammonia excretion rate (NR) (P<0.05), but the interaction of the two factors did not affect OR or NR (P>0.05). OR and NR increased along with rise in temperature (12−24℃) and reached the peak value at 24℃, but then started to decrease as the temperature continued to increase. At 12−28℃ OR and NR of the large size group (A group) were both lower than those of the small size group (B group). At 12−28℃, the O and N mole ratio varied between 8.17 and 17.31 and reached the highest at 20 and 24℃, and the ratio dropped at 28℃. (2) Salinity and body size alone also had significant effects on OR and NR (P<0.05) whereas the combination did not (P>0.05). At salinity 20−30, OR and NR increased along with salinity, and the peak value appeared at salinity 30, followed by a decrease as the salinity continued to rise. At salinity 20−40, OR and NR of A group were both lower than those of B group. The O and N mole ratio varied between 10.80 and 22.71, and the highest value appeared at salinity 30 before it began to fall along with further increase in the salinity. This study indicated that the optimum temperature and salinity for C. cecillei could be 24℃ and 30 respectively, and provided basic data for the development of the farming of C. cecillei.

Abstract:When mariculture Sacharina japonica decay, a large amount of nutrients will be released into the ocean, which will affect the stability in the marine ecosystem. In a 27-day experiment, we investigated the decay rate of Sacharina japonica in the Sanggou Bay and how this process be affected by environmental condition. To determine the effects of the sediment and dissolved oxygen (DO), we set up two conditions including the sediment-containing group and the sediment-free group, and other two conditions about DO including aerobic or anaerobic group. Fluxes of DIN, DON, TN, DIP, DOP and TP were determined during the incubation period. The results were shown as follows: (1) At the end of experiment, the fluxes of DIN, TN, DIP and TP in sediment-containing group were 1.234, 1.802, 0.028, and 0.033 µmol/(g×d) respectively, which were significantly higher than those in the sediment-free group, suggesting that sediment could promote the decay of kelp. However, the flux of DON [0.568 µmol/(g×d)] was significantly lower than that of the sediment-free group. (2) Anaerobic conditions facilitated the release of P from kelp debris and more DOP was released than DIP. The decay rates of TP, DIP and DOP were significantly higher in the anaerobic conditions. However, the release rate of DIN and TN [0.097 μmol/(g×d)] under anaerobic conditions was only 8% and 71% of those under aerobic conditions respectively. (3) The N:P ratio significantly increased to 207.83±301.37 in the sediment-containing group, whereas it decreased to 9.38±6.55 under the anaerobic condition, both of which were distinct from the control group 16.82±1.26. These values were also largely different from the value of Redfield (16:1). Our results suggested that the decay of S. japonica detritus was a fast process and that intensified detritus decay could alter the concentrations and structure of nutrients.

Abstract:The sea cucumber Apostichopus japonicus is one of the most important aquaculture species in China. In recent years the sustainable development of sea cucumber culture has been hindered in China due to issues such as the depletion of natural resources, the genetic degradation, and frequent outbreaks of diseases. Hybridization has been an effective solution to these issues and improving the breeding in aquaculture. Therefore in this study we investigated the temperature and salinity tolerance in the inbred and hybrid offspring of Chinese and Korean sea cucumber populations. Four hybridized combinations were created with complete dual cross, including C(♀)×C(♂), K(♀)×K(♂), K(♀)×C(♂), and C(♀)×K(♂). Four groups of sea cucumber were acclimated at 16℃ and 31 psu for 7 days. The temperature tolerance was estimated in two ways: transferring the subjects directly into high-temperature seawater (27℃, 28℃, 29℃, 30℃, and 31℃) or raising the temperature gradually at 1℃/h. In the salinity tolerance trials, the salinity of acclimated seawater was increased or decreased at 2 psu/h to determine the SSMin (survival salinity minimum), CSMin (critical salinity minimum), SSMax (survival salinity maximum), and CSMax (critical salinity maximum), respectively. The sea cucumbers were also transferred directly into a series of high salinity (36, 38, 40, 42 and 44 psu) and low salinity (21, 19, 17, 15, 13, and 11 psu) to measure the USTL (upper salinity tolerance limit), and LSTL (lower salinity tolerance limit) respectively. It was found that when the seawater temperature increased gradually, the STMax (survival temperature maximum) of C(♀)×K(♂) and C(♀)×C(♂) group were significantly higher than K(♀)×K(♂) group, the 50%CTMax (50% critical temperature maximum) of C(♀)×K(♂) and C(♀)×C(♂) group were significantly higher than other two groups (P˂0.05). When the seawater temperature increased abruptly, the LT50 (median lethal temperature) of both hybrid groups were higher than that of the Korean population, but lower than that of the Chinese population. One-way analysis of variance showed that when the seawater salinity increased gradually, the 50%CSMax (50% critical salinity maximum) of C(♀)×K(♂) group was significantly higher than K(♀)×K(♂) group (P˂0.05); the 50% CSMin (50% critical salinity minimum) of K(♀)×C(♂) group was significantly lower than K(♀)×K(♂) group (P˂0.05). When the seawater salinity decreased abruptly, the LSTL (lower salinity tolerance limit) of K(♀)×C(♂) group was significantly lower than K(♀)×K(♂) group (P˂0.05). These results suggested that the intra-species hybrids might have moderate heterosis in heat and salinity tolerance. Therefore crossbreeding may effectively improve the stress resistance of A. japonicus.

Abstract:Ecosystem-based fishery management (EBFM) is becoming a hot spot and prioritized in fishery industry. Implementation of EBFM requires innovative methodology for marine food-web studies. In this article, we reviewed the theories and methods of food-web topology that was a newly developed research area in ecology. Food-web topology is the quantification of food-web structures based on topological indicators. Models of food-web dynamics are needed to evaluate the impact of fishing and to develop sustainable fishery strategies. Theories and methods of establishing fishery population dynamics model have progressed in the past decades. An important notion in the fish feeding ecology is that body size acts as a determining factor in feeding activities such as selection of preys based on their sizes. Models of size-structured fishery population dynamics have been well developed and can be used to develop the biomass model of species within the food-web. Therefore, it could be valuable strategy for EBFM to combine studies on food-web topological model, size-structured population biomass model, and size-dependent fishing process quantification. Pilot studies on practical approaches should be conducted with high-quality food-web data and fishery statistics, for example, long-term fishery.