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Abstract:The distribution of species diversity is one of the important issues in ecological research. Although spatial interpolation has been widely used in this research. Taking the diversity of nekton in the Yellow Sea and north East China Sea in May 2017 as an example, the species number (S), Shannon-Weaver diversity index (H'), Pielou evenness index (J), and Margalef richness index (d) were selected to evaluate the distribution of species diversity in the sea area. We applied inverse distance weighted (IDW), radial basis function (RBF), local polynomial interpolation (LPI), ordinary kriging (OK), and ordinary cokriging (COK) methods to the above four species diversity indices, and we selected the spatial interpolation method suitable for each species diversity index by the jackknife method. The results showed that COK had the best results for the four species diversity indices with the highest accuracy. The accuracy of the other four methods had little difference and was low. The COK prediction results revealed that both S and d showed an obviously high pattern in the southeast, followed by the north; the lowest pattern was observed in the middle. H' and J were also lowest in the middle, but the difference between the southern and northern sea was negligible in both these indices, and the reasons need to be further explored. The four diversity indices were roughly the same in the high value area of the south of 32°N. The results showed that COK can be used as a spatial interpolation method for nekton diversity in the Yellow Sea and northern East China Sea.

Abstract:To collect reference material for the construction and management of artificial reefs in Dashentang, community characteristics of attaching organisms on the artificial reefs built in different years were evaluated. Three artificial reefs were lifted in September 2018 from reef areas built in 2010, 2012, 2014, 2016, and 2018. The attaching organisms were collected for analysis. The species and number of attaching organisms were different for artificial reefs built in different years. Nonetheless, Crassostrea gigas was a dominant species of attaching organism on all artificial reefs, and in some years it was the only dominant species. These results might be related to the biological environment in the area of sea where the artificial reefs were built. The artificial reef area in our study was adjacent to a natural oyster reef area in Tianjin where the resources for C. gigas were very rich. This was likely the main factor resulting in C. gigas being the absolute dominant species. Because of the short intervals between the time of the survey and when reefs were built, the biological community of attaching organisms had not yet fully formed. Thus, species number, organism number, biomass, Shannon-Wiener diversity index, and Pielou’s evenness index for attaching organisms on reefs built in 2018 were significantly lower than those in earlier years. The species number and organism number of the attaching organisms on reefs built in 2010 were significantly higher than those in other years, but no significant difference in biomass was observed between the parameters for attaching organisms on reefs built in 2010, 2012, 2014, and 2016. The results suggested that species of attached organisms on artificial reefs are greatly affected by the environment in which the reefs were built. The effect of time on the attached organisms was more obvious in the early stages after the reefs were built. When the biomass of attached organisms reached a certain value, the effect was significantly reduced. However, its biological environment continued to slowly improve and its biodiversity gradually increased.

Abstract:The beam trawl is a common fishing gear in the Bohai Sea area and is associated with significant by-catch rates because of its poor selectivity. To improve the selectivity of codend mesh, the authors conducted selective experiments on the codend mesh of beam trawls in the Laizhou Bay during September 2017. A cover net method was used and five kinds of codends (mesh sizes of 15, 25, 35, 45, and 55 mm) were studied. Results show that beam trawls had a poor selectivity for catch species, capturing most of the benefic species in the operating area. Escape rates of the catch in weight, number, and value increased with codend mesh size. The 50% selectivity body length (L0.5) and selection range of Cynoglossus joyneri, Oratosquilla oratoria, Trachypenaeus curvirostris, and Alpheus japonicas linearly with mesh size. The L0.5 of O. oratoria and T. curvirostris appeared to exhibit a linear relationship with codend mesh size (m). Linear regression equations of L0.5=1.472m+12.63 (R2=0.934) and L0.5=1.394m+ 0.724 (R2=0.920), were derived for the respective species. To protect economically valuable species such as O.oratoria, T. curvirostris, the authors suggest enlarging the minimum mesh size for beam trawls to 45 mm, which would maintain production efficiency and protect juvenile fish resources.

Abstract:The grass carp Ctenopharyngodon idellus is one of the main economic fish species for release and resource enhancement in China. In this study, the otoliths of larval grass carps were marked for 1 d by alizarin complexone (ALC) to confirm the feasibility and appropriate conditions for the method. The results showed that lapillus, sagitta, and asteriscus could be successfully marked. The marking rings were observed under both visible light and fluorescence, the latter of which was most obviously observed using blue excitation light. Overall, lapillus had the best marking effect, followed by sagitta. ALC immersion had no significant effect on fish survival and growth. The appearance and disappearance of fluorescent signals on the otolith, the beginning and end of immersion of the fish had a time lag of about 12 h. At 60 d of recovery of the culture after immersion, the ALC mark ring was still visible, indicating that the ALC-marked effect was evident and could exist for quite a long time. This method has a strong feasibility for marking and effect assessment of the larval grass carp for future resource enhancement and release.

Abstract:This experiment investigated the effects of dietary vitamin B6 content on growth performance, body composition, liver enzyme activities, and transaminase gene expression in juvenile rockfish (Sebastes schlegeli). Six experimental diets were formulated with different levels of vitamin B6: 2.08 (control group), 3.25, 4.16, 6.32, 10.17, 31.14 mg/kg. The juvenile rockfish average initial body weight was (36.35±0.06) g. After 9 weeks of treatment, the results showed that, with an increase in dietary vitamin B6 content, the weight gain rate and specific growth rate of the experimental fish initially increased and then decreased, with the largest changes seen in the 4.16 mg/kg group. The viscerosomatic index of the 4.16 mg/kg group was significantly higher than that of the control group (P<0.05). The hepatosomatic and intestine-somatic indexes of the 3.25 to 10.17 mg/kg groups were significantly higher than those in the control group (P<0.05). Muscle moisture content in the 3.25 to 31.14 mg/kg groups was significantly lower than in the control group (P<0.05). Crude protein and crude lipids of the whole fish and muscle showed increasing trends and then decreases. The activity of superoxide dismutase in livers increased at first and then decreased, with the 4.16 to 10.17 mg/kg groups showing significantly higher activity than the control group (P<0.05). Malondialdehyde content also decreased and then increased, with the 3.25 to 31.14 mg/kg group showing significantly lower content than the control group (P<0.05). Liver vitamin B6 content increased at first and then stabilized. The activities of glutamic oxalacetic transaminase and glutamic-pyruvic transaminase in the 3.25 to 31.14 mg/kg groups were significantly higher than in the control group (P<0.05). The relative expression level of GOT1 and GOT2 genes increased at first and then decreased, with the 3.25 to 31.14 mg/kg groups showing significantly lower expression levels than the control group (P<0.05). Relative expression level of GPT1 and GPT2 genes increased at first and then decreased, reaching a maximum in 6.32 mg/kg group. Relative expression of the tyrosine aminotransferase gene increased at first and then decreased, with the 4.16 to 10.17 mg/kg groups showing significantly higher expression levels than the other groups (P<0.05). Relative expression of the serine transaminase gene decreased, with expression levels in the 4.16 to 31.14 mg/kg groups significantly lower than in the control and the 3.25 mg/kg groups (P<0.05). A broken-line regression analysis of the WGR, liver vitamin B6 content, and GPT parameters showed that the dietary vitamin B6 requirement of juvenile rockfish with a body weight of 36 g was 3.52 to 6.32 mg/kg.

Abstract:This study aimed to investigate the morphological and histological features of the digestive system of Schizothorax biddulphi using conventional HE-stained paraffin sections. The digestive system of S. biddulphi consisted of a digestive tract and a digestive gland. The digestive tract comprised the oropharynx, esophagus, and intestine (anterior intestine, middle intestine, posterior intestine, and rectum). A pharyngeal tooth had developed in the oropharynx, but no stomach was present; the intestine adjoined the esophagus and the anterior intestine was inflated. The general structure of the digestive tract consisted of the mucosa, submucosa, muscular layer and serous membrane; however, the oropharyngeal cavity only had the mucosa and muscular layer. The mucosal layer showed the greatest difference, mainly in the following aspects. First, the tunica mucosa of the oropharynx was made of a stratified squamous epithelium with taste buds and numerous mucous cells. Second, the esophagus was thick and short, and the mucosa consisted of a stratified squamous epithelium. Third, there was a large number of blood vessels in the lamina propria. Last, the intestinal epithelial cells were single columnar epithelial cells, and the number of goblet cells increased gradually from the anterior intestine to the rectum, while the mucosal fold height gradually decreased. The digestive gland of S. biddulphi is composed of a liver and pancreas. The hepatic lobule of the liver was not obvious, but the distribution of hepatic sinuses and central veins was regular, however, the portal area of the liver was not typical. The pancreas was an independent structure, separated from the liver, and not found in any tissue other than the mesentery. The veins were more obvious in the pancreatic lobule, and there were numerous nucleated red blood cells in the vascular system. The relationship between morphological and histological features of the digestive system and feeding behavior of S. biddulphi was discussed, in order to enrich the biological research of S. biddulphi and to provide a theoretical basis for the analysis of its trophic behavior and development of its bait.

Abstract:Exhaustive exercise often occurs in shrimp farming and in the wild. Giant tiger prawn (Penaeus monodon) is an important species in aquaculture and proliferation in China's coastal areas. The study used dip nets to chase juvenile P. monodon in the indoor sink, simulated the exhaustive exercise experiment, and explored the recovery process of antioxidant capacity after exhaustive exercise; however, there was no report on the physiological recovery process after the exhaustive exercise of P. monodon. The results showed the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), and malondialdehyde (MDA) content in juvenile P. monodon at 0 h after exhaustive exercise. No significant difference from the control group was observed. At 1~12 h, the activities of SOD, CAT, POD, MDA content, and T-AOC continued to decrease, whereas the activity of GSH-Px did not change significantly. At 24 h, the activities of SOD, CAT, and POD were significantly lower than those of the control group, and the activity of GSH-Px, MDA content, and T-AOC were significantly higher than those of the control group. At 72 h, the activities of SOD and CAT were still significantly lower than those in the control group. The activities of GSH-Px, POD, and MDA content were restored in the control group, and T-AOC activity was still significantly higher compared to that in the control group. This indicated that the enzymatic antioxidant system of P. monodon was not activated during exhaustive exercise. At 24 h after exhaustive exercise, the antioxidant capacity at 72 h was still at a high level. It was observed that the enzymatic antioxidant system was not activated in juvenile P. monodon during exhaustive exercise. The antioxidant capacity of juvenile P. monodon is lower within 24 h after exhaustive exercise, then increases significantly after 24 h of exhaustion and remained at that level for a long time. Within 24 h after exercise, further stimulation of juvenile P. monodon should be avoided.

Abstract:This study compared the effects of different photoperiods (D, 10L:14D, 14L:10D, L) on the growth, molting and glucose metabolism of Marsupenaeus japonicus. The results showed that different photoperiods had significant effects on the growth, molting, and glucose metabolism of M. japonicas. With the extension of illumination time, the survival rate (SR), specific growth rate (SGR), and molting rate (MF) of these shrimps decreased gradually. By day 49, the mortality of the shrimps in the group L reached 100%. At the end of the experiment, SR, SGR, and MF were significantly higher in the group D (60.000±2.722)% than in the 10L:14D (6.966±0.686)%/d and 14L:10D (4.667±0.363)%/d groups (P<0.05). However, the differences in SR, SGR, and MF between the 10L:14D and 14L:10D groups were not significant. Different photoperiods significantly affected the concentration of molting inhibitory hormone (MIH) and ecdysone hormone (EH) in Japanese prawns. On day 30, the concentration of MIH was significantly lower in the group D than in the 10L:14D, 14L:10D, and L groups (P<0.05), and the concentrations of MIH were significantly lower in the 10L:14D and 14L:10D groups than in the group L (P<0.05); the differences in the 10L:14D and 14L:10D groups were not significant. On day 60, the concentration of MIH was significantly lower in the group D than in the 10L:14D and 14L:10D groups (P<0.05), but the differences between the two groups were not significant. The concentration of EH in the shrimps decreased continuously with the extension of the illumination time. On day 30, the concentration of EH was significantly higher in the group D than in the 10L:14D, 14L:10D, and L groups (P<0.05); however, there were no significant differences between these three groups. On day 60, the concentration of EH was significantly higher in the group D than in the 10L:14D and 14L:10D groups (P<0.05), but the differences between the two groups were not significant. Different photoperiods significantly affected the glucose metabolism of shrimps, and the changes in serotonin (5-HT), crustacean hyperglycemic hormone, and glycogen phosphorylase levels in the hepatopancreas of different treatment groups showed the same trend as the concentration of MIH mentioned above, whereas the changes in glutamine synthetase levels in the hepatopancreas exhibited an exactly opposite trend. Taken together, these findings indicate that a dark state is the most suitable environment for optimum growth of the Japanese prawn.

Abstract:In this study, we examined the effects of chronic nitrite stress on the growth, feeding, body composition, and glucose metabolism of Litopenaeus vannamei [(2.03±0.33) g]. The experiment lasted for 36 days, and there were control group, N8, N15, and N30 (stress groups) with concentrations of 0, 8, 15, and 30 mg/L NO2–-N. With increasing NO2–-N concentrations, the final body weight, specific growth rate, weight gain rate, and feeding rate of the shrimp showed a significant decline. At day 18, the blood glucose and glycogen in the hepatopancreas in the N8 and N15 groups were higher than those in the control group; however, they were lower than the control group by the end of the experiment. The muscle glycogen in the stress group was always lower than the control group during the experiment. In addition, the activity of hexokinase in the muscle of the stress group was lower than that of the control group, whereas the activity of hexokinase and pyruvate kinase in the hepatopancreas of the stress group was significantly higher than that of the control group. Further, the activity of lactate dehydrogenase in the hepatopancreas first increased and then decreased, but there was no significant difference compared with the control group. In the final body composition, there was almost no change in the water and crude protein of each group, but the crude lipid content of the N30 group was significantly lower than that of the control group. The above results indicated that chronic stress of nitrite can reduce the appetite and slow down the growth in shrimps. The glucose metabolism in shrimp is only a short-term response model to cope with the chronic stress of nitrite. At the same time, according to the change of crude lipid, it is speculated that the lipid metabolism of L. vannamei played an important role in the chronic nitrite stress for the shrimps.

Abstract:To study the correlation of biological traits between male and female mantis shrimp (Oratosquilla oratori), eight biological indicators, total length (TL), body length (BL), carapace length (CL), tail fan length (FL), abdominal length (AL), abdominal width (AW), large pincers length (LL), and wet weight (Y) were measured. The influence of morphological traits on body weight was studied using correlation analysis and path analysis. The regression equations representing the effect of morphological traits on body weight were established using the stepwise regression method, and the curve models of seven shape traits and body weight were fitted. The results showed that the variation coefficient of body weight was greater than that of the morphological traits, and quantitative traits such as FL, AW, LL, and Y were significantly different between male and female O. oratori (P<0.01) .The correlation of the quantitative traits reached a very significant level (P<0.01) among the female, male, and mixed populations. In the relationship of morphological traits, the correlation coefficients of TL to BL were largest in the female group, the male group, and the mixed group (0.984, 0.993, and 0.988, respectively); regarding the relationship of morphological traits to body weight, the correlation coefficient of TL to body weight was highest in the female group (0.973), the correlation coefficient of BL to body weight was largest in the male group (0.974), and the correlation coefficient of AW to body weight was largest in the mixed population group (0.969). The greatest direct effect on body weight in females and mixed populations was AW (diameter coefficients of 0.418 and 0.508, respectively), and the direct effect on body weight was the greatest in male BL (diameter coefficient, 0.613). The direct determination coefficient of AW to body weight was the highest in the female group and the mixed population group (0.175 and 0.258, respectively), and the direct determination coefficient of BL to body weight was the highest in the male group (0.376). TL, AW, and CL are mainly considered for the female population, BL and AW are mainly considered for the male population, whereas AW and TL are mainly considered for the mixed population. The regression equations of female, male, and mixed populations with morphological traits as independent variables and body weight as dependent variables are: Y1=–48.499+0.315XTL+1.159XAW+ 0.186XCL(R2=0.978), Y2=–55.987+0.453XBL+1.152XAW(R2=0.959), and Y3=–51.651+1.738XAW+0.274XTL (R2=0.960). The optimal fitting models of morphological traits to body weight of O. oratori include the linear model, power function model, and exponential function model. The same types of optimal fitting models are used except for TL, AL between male and female O. oratoria; in addition, nothing else is the same. This study can provide a theoretical basis for the selection of O. oratori.

Abstract:Heavy metal pollution in marine environments has become a prominent environmental problem. Many domestic and overseas scholars have conducted a great deal of research on the heavy metal pollution characteristics and accumulation specificity in crustaceans. Economically important crustaceans in aquaculture such as the Whiteleg shrimp (Penaeus vannamei), Summer flounder (Paralichthys dentatus), yellow croaker (Larimichthys crocea), Chesapeake blue crab (Callinectes sapidus), and Japanese blue crab (Portunus trituberculatus) are very popular foods but also have a high arsenic-enrichment factor. One of the most economically important marine aquaculture crabs in China, P. trituberculatus, has recently increased in popularity due to its high nutritional value and desirable flavor. The bioaccumulation of arsenic in the Gazami crab (Portunus trituberculatushas) has not been reported. Exploring the accumulation specificity of arsenic in P. trituberculatus provides the scientific data necessary to determine safe thresholds and arsenic limit in marine aquaculture. In our study, bioaccumulation of arsenic was studied in P. trituberculatus and simulated using the two-compartment model. The exposure concentration gradients of arsenic were 5, 20, and 100 μg/L. We analyzed data with non-linear curve fitting, obtaining the kinetic parameters such as bioconcentration factor (BCF), uptake rate constant (k1), elimination rate constant (k2), and biological half-life (B1/2). The results showed that the BCF of arsenic in the hepatopancreas was significantly higher than muscle. At the end of the enrichment experiment, the BCFs of arsenic in the hepatopancreas tissues of P. trituberculatus from low to high concentration groups were 21.21, 15.07, and 10.31, respectively. The uptake rate constant k1 and the BCF decreased with the increase of the aquatic arsenic concentration. The BCFs of arsenic in the muscle from low to high concentration groups were 5.17, 3.74, and 5.83, respectively. The kinetic parameters of the 5 μg/L and 100 μg/L experimental groups were similar. However, the uptake rate constant k1 was the smallest. The elimination rate constant k2 was the largest in the 20 μg/L experimental group, while the BCF and B1/2 were the smallest.

Abstract:Based on Dame indices and Herman model, the carrying capacity of Manila clam (Ruditapes philippinarum) in Jiaozhou Bay is estimated with the comprehensive fishery survey data, field simulation experiment, and growth tracking data between July 2017 and April 2019. The results showed that the average chlorophyll a concentration was in the range of 2.09~4.28 mg/m3, with an average value of 3.07 mg/m3. The average clearance rate was 0.45 L/(h∙ind.) and converted to a unit-mass based value was 2.52 L/(g∙h). The average dry weight of Manila clams at 1, 2, and 3 ages were 0.18, 0.30, and 0.42 g, respectively. The water mass residence time was 52 days, the primary production time was 1.58 days, and the bivalve clearance time was 2.09 days in Jiaozhou Bay. The corresponding carrying capacity of Manila clam were estimated to be 637, 378, and 272 ind./m2 for 1-year, 2-year and 3-year old clams, respectively. Currently, the cultured quantity of Manila clams has exceeded the carrying capacity. It is recommended that the stocking density to be 582 ind./m2 if 2-year clams are considered as the target object, and the stocking density to be 789 ind./m2 if 3-year clams are considered as the target object. The results provide theoretical basis and necessary data for the development of the clam aquaculture in Jiaozhou Bay.

Abstract:To explore the influence of pH on embryo development and larval growth of bay scallop (Argopecten irradia), pH 8.0~8.2 was set as the control group to analyze the influence of different pH (7.6~7.7, 7.3~7.4, 7.0~7.1, and 6.7~6.8) on the development of embryos and larva of bay scallop. The results showed that with decrease in pH, the hatching rate of embryos in each experimental group decreased, the deformity rate increased, hatching time was prolonged, and the larva were significantly smaller than those in the control group (P<0.05). The survival rate and growth rate of D-larvae and top umbo larvae were significantly lower than those of the control group (P<0.05). The survival rates of the pH 7.0~7.1 and pH 6.7~6.8 experimental groups were 6.1% and 5.6%, respectively, and 75.2% in the control group on the 8th day of larva development. The growth rates of each experimental group were 3.4 μm/d and below, except for the pH 7.6~7.7 group, which basically showed a state of growth stagnation. There was a significant difference in the adhesive rate between the experimental group and the control group (P<0.05). On the 7th day, the adhesive rate of the pH 6.7~6.8 experimental group was only 31.7%. The results showed that the change in seawater pH had a significant effect on early embryo and larva development in bay scallop, which provides a reference for the evaluation of the effects of pH change on economic shellfish resources, such as bay scallop and others in the aquaculture industry.

Abstract:The photosynthetic physiology of the different stages of the Pyropia yezoensis free-living conchocelis were investigated at different temperatures (15℃, 25℃, and 35℃) and light intensities [40, 100, and 300 μmol/(m2·s)] to reveal the regulation mechanism and establish a foundation for efficient and accurate P. yezoensis seedling technology. The main results were as follows: 1) At 15℃ and 25℃, the optimum PSⅡ quantum yield (Fv/Fm), gross photosynthesis rate (Pg), and net photosynthetic rate (Pn) of the vegetative conchocelis and conchosporangial branches decreased as light intensity increased. Fv/Fm and Pg of the vegetative conchocelis filaments dropped to zero under 300 μmol/(m2·s) light intensity, and the values of Pn were below zero. The respiratory oxygen consumption rate (Rd) of the vegetative conchocelis was significantly higher than that of the conchosporangial branches at 25℃ and 40 μmol/(m2·s). The difference in the Rd values between vegetative and conchosporangial branches decreased gradually during culturing under the other conditions. In general, Fv/Fm, Pg, and Pn of the conchosporangial branches were significantly higher than those of the vegetative conchocelis filaments and there was no significant difference in Rd between the two developmental stages under most culture conditions; 2) Fv/Fm of the conchosporangial branches was significantly higher than that of the vegetative conchocelis at 6 h of culture at 35℃, which decreased with increasing light intensities. Fv/Fm of the other treatments was nearly zero. Pg and Rd of the conchosporangial branches were higher than or equivalent to that of the vegetative conchocelis after 6 h of culture at 35℃, and 40 or 100 μmol/(m2·s). After 1 d or 2 d, Pn and Rd of the vegetative conchocelis were higher than those of the conchosporangial branches, while the Pn and Rd were all below zero under 300 μmol/(m2·s) conditions during the entire experimental period. Overall, Fv/Fm, Pg, and Pn of free-living P. yezoensis conchocelis were significantly lower (mostly zero or below), whereas Rd was higher at 35℃ than at 15℃ or 25℃. After 1~3 d, both vegetative conchocelis and conchosporangial branches became green or white. In summary, under the light intensity and temperature conditions in which the vegetative conchocelis was severely inhibited, conchosporangial branches had relatively high photosynthetic activity. The present findings indicated that high light intensity and temperature were not beneficial to vegetative conchocelis, but they could stimulate the vegetative conchocelis to turn into conchosporangial branches, and conchosporangial branches have greater resistance ability under high- temperature and light intensity stress.

Abstract:The whole genome of Russian red sea cucumber mitochondria introduced into culture was randomly sequenced and analyzed by high-throughput sequencing. The results show that the genome is 16,111 base pairs (bp) in length, and contains 37 genes, including 22 tRNA, 2 rRNA (l-rRNA, s-rRNA), and 13 protein-coding genes. There are 24 gene-spacing and 5 gene-overlap regions; both the protein-coding gene and the full-sequence pair base exhibit an A and T bias; the highest frequency of amino acid coding is Ser, followed by Leu; and the codon is complete, except ND1 with GTG as the starting codon and the others with ATN as the starting codon. Most termination codons are TAA, but the termination codons of ND2 and ND4 are TTG and TAG, respectively; The length of tRNA ranges from 66 to 72 bp, two genes are duplicated, and 21 genes predict their clover structure. The length and position of l-rRNA and s-rRNA are different, and the use of bases is similar. The gene arrangement of the protein-coding gene is the same as that of Holothuroidea and Echinoidea, and gene models are shared with Asteroidea and Ophiuroidea. A genetic distance analysis shows that the Russian red sea cucumber is closest to Apostichopus japonicus from three habitats. A BLAST analysis shows that Russian red sea cucumbers have the highest homology with A. japonicus. A phylogenetic tree was constructed based on the maximum likelihood method and the amino acid and nucleotide sequences, which provides a theoretical basis for subsequent genetic research of Russian red sea cucumbers.

Abstract:Female specimens of the dwarf form of Sthenoteuthis oualaniensis, the purple flying squid, were collected from light-falling fishery catches from the South China Sea in 2017. The fecundity of this species was investigated and characterized. The results showed that the potential fecundity of female individuals ranged from 1218 to 32843 oocytes. The number of ovarian oocytes ranged from 1178 to 30397 cells, and the number of ripe eggs in the oviducts ranged from 113 to 2904 cells. In addition, the relative fecundity ranged from 48.93 to 842.12 cell/g of a female’s total weight, and the overall potential reproductive investment index varied from 0.005 to 0.213. The potential fecundity showed a significant power regression relationship to mantle length and linear relation to body weight. Relative fecundity showed a significant exponential relation to mantle length and linear correlation with body weight. Potential individual reproductive investment index increased linearly with increasing mantle length as well as body weight. Batch fecundity had an estimated range from 1895 to 2904 cells based on the number of ripe oocytes in the oviducts of late-maturing individuals (stage Ⅵ), and the number of spawn per batch was estimated to range from 6 to 15 with an average of 9.87±4.36. Major axis length of ovarian oocytes was measured and ranged from 0.17 to 0.99 mm with an average of (0.51±0.14) mm. There were significant differences in major axis length of ovarian oocytes among different maturity stages (P<0.05). The frequency of major axis length of oocytes in the ovary showed a unimodal distribution for specimens at stages Ⅲ to Ⅵ. Moreover, the frequency distribution peak showed a forward increase with maturation when the mode was between 0.35 and 0.60 mm for stages Ⅲ and Ⅳ, while it showed a forward increase when the mode was between 0.40 and 0.75 mm for stages Ⅴ and Ⅵ. The major axis length of ripe eggs in the oviducts ranged from 0.50 to 1.08 mm. Cumulatively, these findings indicate that fecundity of the dwarf form of female S. oualaniensis tends to increase as body size increases and as maturation progresses. Furthermore, the ovarian oocytes develop in a pattern of group-synchrony, and ovulation occurs multiple times.

Abstract:To better protect the resource of Sepia esculenta, we need to understand its population genetic structure. In the field of genetics, microsatellites have become important molecular markers for genetic diversity and marker-assisted breeding, because of their unique advantages, such as abundant polymorphism, rich information, codominance, and conservation. In this study, 177,951 unigenes obtained via transcriptome sequencing of the golden cuttlefish were used to detect and analyze the simple sequence repeat (SSR) loci information using Micro Satellite (MISA) software. The results showed that 161,327 SSR loci were detected in the transcriptome of S. esculenta, which are distributed in 64,933 unigenes with a distribution frequency (of SSR loci) of 36.49%, and the frequency of occurrence was 90.66%. Among them, the main types of repeats were mononucleotide, dinucleotides, and trinucleotides, which accounted for 46.00%, 39.93%, and 9.48% of the total SSR, respectively. Among the repeat motifs contained in the SSR, A/T was the predominant repeat type of a mononucleotide, and AT/AT and AC/GT were the dominant repeat types of dinucleotides. There were 66,004 repeat motifs with a length of ≥ 20 bp, accounting for 40.91% of the total number of SSRs, and the number of SSR loci in which low-level motifs (di- and trinucleotide repeats) are dominant. The above results indicated that SSR loci in the transcriptome of golden cuttlefish had a high frequency and a rich variety, and high polymorphic potential. The results provided a powerful reference for the better development of SSR molecular markers and the protection and utilization of S. esculenta germplasm resources, genetic diversity evaluation, and future molecular marker-assisted breeding.

Abstract:The loop-mediated isothermal amplification (LAMP) detection method of Decapod iridescent virus 1 (DIV1) was established and optimized based on primers designed from the DIV1 capsid protein gene in present study. Analytic sensitivity of the newly established method was assessed using the pMD18-DIV1 plasmid standard as a template, and the detection specificity was also determined. The results showed that the optimal reaction temperature for the DIV1-LAMP method was 64.4℃, and the optimized 25 μl reaction system contained 2.5 μl 10×isothermal amplification buffer, 4.0 mmol/L Mg2+, 1.2 mmol/L dNTPs; 6.4 U Bst 2.0 WarmStart® DNA polymerase and 0.8 μmol/L EvaGreen®. The detection limit of the new method was 3.54×102 copies/reaction; it did not cause a cross-reaction with major shrimp pathogens such as Enterocytozoon hepatopenaei (EHP), Vibrio causing acute hepatopancreatic necrosis disease (VpAHPND), covert mortality nodavirus (CMNV), infectious hypodermal and hematopoietic necrosis virus (IHHNV), white spot syndrome virus (WSSV), Taura syndrome virus (TSV), or yellow head virus (YHV). The newly developed method showed good repeatability and stability. The on-site, rapid, highly sensitive detection method of DIV1 was established by replacing EvaGreen® with GeneFinder® which was preset in the cap of the reaction tube. The DIV1-LAMP real-time fluorescence and on-site LAMP detection method established in this study is sensitive, specific, and rapid. This novel method will provide new technical options for the qualitative, quantitative, and rapid on-site detection of the emerging DIV1, which will benefit the shrimp farming industry by facilitating the monitoring, early warning, and prevention of DIV1.

Abstract:Secreted proteins are synthesized in cells and secreted to function outside the cell. They play an important role in the manipulation of host cells and the virulence of many eukaryotic protozoan parasites. Enterocytozoon hepatopenaei (EHP) is an obligate intracellular parasite that can infect a variety of economically valuable shrimp species, and is one of the most serious diseases affecting global shrimp production. Here, we predict the secreted proteins of the EHP genome with the EuSecPred2.0 pipeline and analyzed the length of these secreted proteins, the length of the signal peptide, and the amino acid distribution at the cleavage site, and annotated the function of secreted proteins. The results show that the length of the secreted proteins ranged from 30 to 400 amino acid residues, the signal peptides covered approximately 9~32 amino acids, and the cleavage sites of the signal peptides were mainly composed of hydrophobic amino acids. Motif analysis revealed a NV[VT][IK]CA[ED][SA] motif in signal peptides. Functional annotation of proteins revealed that a variety of key proteins are involved in adhesion and infection of microsporidia, regulation of cell cycle, and immune response. The results shed light on the infection mechanism of EHP and provide a theoretical basis for further defining the pathogenic factors of EHP.

Abstract:To understand the drug resistance and virulence genes of Vibrio parahaemolyticus in shrimp culture ponds, we collected and isolated V. parahaemolyticus from shrimp culture ponds in four different areas of Shandong Province in 2018. The Kirby-Bauer disk method was used to detect the resistance of V. parahaemolyticus to 12 antibiotics, and PCR was used to detect the heat-resistant direct hemolysin gene (tdh) and heat-resistant-related hemolysin gene (trh). A total of 50 V. parahaemolyticus strains were isolated from the shrimp culture ponds. Drug susceptibility test showed that the resistance of V. parahaemolyticus to gentamicin, neomycin sulfate, and ampicillin were high at 98%, 90%, and 86%, respectively. The susceptibility rates to florfenicol, chloramphenicol, and ceftazidime were higher, and the resistance rates were 10%, 10%, and 20%, respectively. Overall, 88% of the strains showed multidrug resistance. The virulence gene test showed that all the strains lacked the tdh gene and 4% of the strains were trh-positive. This study suggests that the antibiotic resistance of V. parahaemolyticus in a shrimp aquaculture environment is concerning. Etiological surveillance of V. parahaemolyticus should be strengthened, and antibiotics should be reasonably used in the aquaculture process to realize the healthy development of the aquaculture industry.

Abstract:The effects of adding clove oil on the storage quality of crab cream and shrimp sauce have been studied in terms of MDA content, total sulfhydryl (T-SH) content, fatty acid composition and content, free amino acid content. and taste nucleotide content. Here, taste activity value and equivalent umami concentration (EUC) were used to evaluate the taste strength of these ingredients, then combined with other items to comprehensively analyze the storage quality of crab cream and shrimp sauce. The results showed that after 180 days of storage, MDA content with added clove oil was lower than without clove oil, but adding clove oil produced higher T-SH levels. After the same storage period, the saturated fatty acid content without added clove oil was significantly higher than with clove oil. However, monounsaturated and polyunsaturated fatty acid content showed contrary results. GMP, IMP, and AMP were significantly reduced after 180 days of storage without clove oil, but AMP levels with clove oil significantly rose during the same storage period. The total taste nucleotide content with and without clove oil was reduced significantly. All free amino acids improved with and without clove oil during storage, but the total free amino acid content, flavor amino acid content, and sweet amino acid content were significantly higher with clove oil than without. GMP, IMP, Glu, Ala, Val, Lys, and Arg are major constituents of crab cream and shrimp sauce. The EUC without clove oil rose from 1691 g MSG/100 g to 3039 g MSG/100 g. However, after adding clove oil, it rose from 2058 g MSG/100 g to 3809 g MSG/100 g after storage. The results suggest that clove oil has fat and protein anti-oxidation effects, and improves the storage stability and flavor of crab cream and shrimp sauce.

Abstract:Reef fish are expensive, but owing to overdevelopment, environmental pollution, and global warming, reef fish resources are collapsing and their habitats are undergoing varying degrees of degradation. In order to solve the stress in the global marine ecological environment and its resources, the construction of marine ranching based on artificial reef and stock enhancement and release has become the main strategy for protecting aquatic organisms in coastal countries. By researching the behavioral ecology of reef fish, analyzing their reaction to reef structure and artificial habitat and the effect of artificial environments on fish, the fish release strategy will be optimized, survival rate will be increased, resources will be protected, and artificial reef constructions will be more scientific. Therefore, in this paper, research progress on the behavioral ecology of reef fish, both in China and abroad, was summarized, including habitat selection and foraging, aggression, territorial and defensive behaviors. Moreover, the importance of reef fish behavioral ecology on resource protection and development was analyzed. Meanwhile, existing problems in the behavioral ecology of reef fish were discussed, and suggestions put forward, to provide a more scientific theoretical basis and more efficient technical scheme for the development of marine ranching in China.

Abstract:Salmon and trout are typical cold-water fishes with high economic values; they are among the most important economic fishes in the world. However, with increasing aquaculture density, the aquaculture environment is becoming increasingly degraded. The occurrence of salmon and trout parasitic diseases and corresponding damage to fishes are also increasing. These factors severely restrict the healthy development of the industry. Common and severe parasites of salmon and trout are Gyrodactylus, Caligus rogercresseyi, Neoparamoeba perurans, Myxobolus cerebralis, Tetracapsuloides bryosalmonae, and Kudoa spp. These parasites have simple life cycles and rapid reproduction rates. Most of them inhabit the skin and various organs of the fish body, thereby slowing growth and weakening the resistance of the fish. This effect damages the fish body and eventually kills the fish. Physical control methods and chemicals are used in combination for comprehensive prevention and control. This paper reviews the research progress and achievements in the field of the common parasitic diseases of salmon and trout to provide useful references for the research and control of such diseases.