Abstract:The ribosomal RNA gene (rDNA) cluster consists of multiple units of three coding genes (18S, 5.8S, and 28S) as well as two internal transcribed spacers (ITS1 and ITS2) separating the coding regions. Thus far, studies on these five fragments mainly focused on the polymorphism of different copies within each individual sample and identification of useful markers for phylogenetic relationship analysis. However, there are limited studies related to the features of GC content, which is a very important characteristic of ribosomal RNA gene. The characteristics of rDNA GC content and whether the GC balance phenomenon exists in the coding regions in fishes were investigated by selecting 11 species from five families of Perciformes, including Latidae, Toxotidae, Rachycentridae, Xiphiidae, and Carangidae. In all, 1651 monoclones from the five fragments mentioned above were obtained. The GC content features were analyzed based on the sequences from the 11 species or the datasets from other teleostean fishes retrieved from GenBank. The results from the above two analyses were compared. The following results were obtained. First, the GC content of 18S, 5.8S, 28S, ITS1, and ITS2 ranged from 52.6% to 57.1% (average, 54.6%), 55.6% to 58.9% (average, 57.4%), 64.2% to 65.8% (average, 64.6%), 56.5% to 73.0% (average, 65.0%), and 62.3% to 77.5% (average, 69.1%), respectively. Second, compared with non-coding regions, coding regions were relatively conserved. The GC content of the coding genes varied in smaller ranges than those of the internal transcribed spacers. The GC contents of 18S and 5.8S were lower than those of ITS1 and ITS2, but that of 28S was between the lowest and highest values of ITS1 and ITS2. Therefore, we found that the GC content of non-coding regions was higher than 60%, which was a remarkable characteristic of these fishes, and no correlation was found between fragment length and higher GC content. Further, no obvious G, C, or GC rich block was found in the high-GC-content regions of ITS1 and ITS2 sequences. Third, the similarity of GC content between ITS1 and ITS2 within the same species could be higher or lower than that of the same fragment among different species within the 11 species. Therefore, the GC balance phenomenon is not universal and only exists in species whose intra-species GC content similarity is lower than the inter-species GC content similarity. The results of this study might provide a scientific basis for further studies and facilitate the utilization of the ribosomal gene characteristics of fish.

Abstract:is one of the most important aquaculture species in the world, cultured in a cage culture system, which was introduced to China in 2010 and in recirculating aquaculture system (RAS). In order to investigate the effects of dietary fat and protein levels on fat metabolic enzymes and growth associated gene expression of in RAS, a 3×2 (three fat levels:18%, 21%, and 24%; two protein levels:38% and 48%, represented by F₁8, F21, F24, P38, and P48, respectively) random two-factor animal trial was conducted for 56 days. The trial included six treatments with triplicate groups of 40 trial fishes (650.00±45.50) g. Results showed that:(1) The fat requirement of was lower in RAS than in cage culture system, and the requirement of protein was equal between the two systems. The weight gain rate (WGR) was significantly higher in P48F21, by 22.23%-125.86%, than that in other groups (<0.05), while the feed conversion rate (FCR) was significantly lower in P48F24, by 16.24%-30.00% than that in other groups (<0.05). (2) High fat level significantly increased hepatosomatic index (HSI) (<0.05), while high protein level decreased condition factor (CF) very significantly (<0.01). The HSI was significantly higher in P48F24 group than in other groups, by 10.92%-28.16% (<0.05), while the CF was significantly lower than that in other groups, by 10.24%-12.31%. The study proposed the primary nutrition project that can control the shape of to 600-900 g by weight. (3) High and medium fat levels significantly (<0.05) increased the activity of lipoprotein lipase (LPL), hepatic lipase (HL), and total esterase, while high protein level significantly (<0.05) increased the activity of LPL and total esterase. The activities of LPL, HL, and total esterase in P48F21 and P48F24 groups were significantly higher than those in other groups (<0.05), and especially the activity of LPL in the two groups was higher than that in the P38F₁8 group, in which the activity of LPL was the lowest (<0.05). We also found a significant negative correlation between protein level and the activity of fatty acid synthase (FAS) (<0.05). (4) Medium fat level increased the expression of IGF-I gene in muscle and liver extremely significantly (<0.01), while high protein level increased the expression of GH and IGF-I genes in muscle and IGF-I gene in liver extremely significantly (<0.01). The expression of GHR decreased significantly with the increase in fat or protein level (<0.05). The expressions of GH and IGF-I genes in muscle and IGF-I gene in liver in P48F21 and P48F24 groups were significantly higher than those in other groups (<0.05), while the expression of GHR in muscle and liver was lower than that in other groups (<0.05). We found negative correlations among GH, IGF-I, and GHR, which could control the growth and reproductive activities in appropriate ranges. In conclusion, P48F21 and P48F24 groups had obvious promoting effects on growth performance and growth-associated gene expression in , while P48F21 group was better in the use of fat and saving of costs.

Abstract:Saline-alkaline water bodies are widely distributed in China. High alkalinity is one of the main stressors for the survival of aquatic animals in saline-alkaline water. Previous studies have established that ammonia excretion is inhibited when fish are acutely exposed to alkaline water. Przewalskii's naked carp, also known as or the scale-less carp, is endemic to the austere environment of Lake Qinghai. Lake Qinghai has a high salinity (13 ppt) and a strong alkalinity (carbonate alkalinity approximately 29 mmol/L, pH 9.1-9.5). Due to high evaporative water loss and extensive water diversion for agricultural use, the water level of the lake is decreasing by 10 cm per year and the salinity and alkalinity levels are increasing by 7% and 0.5% per year, respectively. Some studies showed that had evolved a variety of mechanisms, such as osmoregulation and ion regulation with low energy consumption, regulation of HCO3-secretion in intestines, and compensatory carbonic anhydrase expression mechanism under metabolic alkalosis, to adapt to saline-alkaline environments. However, the mechanism of nitrogenous waste excretion is less well studied. In order to evaluate the effect of carbonate alkalinity stress on nitrogenous waste excretion in to 32 mmol/L and 64 mmol/L carbonate alkalinity water and measured ammonia and urea excretion rate after -6 h (pre-transfer), 4 h, 8 h, 12 h, 16 h, 20 h, 24 h, 48 h, 72 h, 96 h, and 120 h (recovery) after initial exposure. We also measured Rhesus type b glycoproteins (), and urea transporter ( by real-time PCR. The results showed that in alkaline water reduced ammonia excretion but increased urea excretion. Ammonia excretion rate decreased significantly over the entire exposure period in 32 mmol/L carbonate alkalinity water and the initial exposure period in 64 mmol/L carbonate alkalinity water. Ammonia excretion is expected to be inhibited when fish are subjected to alkaline water because of a decrease in the extent of the protonation of NH₃ to NH₄⁺. Consequently, at high pH water caused by high carbonate alkalinity, the partial pressure of NH₃ (PNH₃) is predicted to rise in water adjacent to the gill, thus reducing the PNH₃ gradient that drives NH₃ diffusion. However, in the 64 mmol/L group, the ammonia excretion rate recovered to the level of pre-transfer after 24-72 h and 8-20 h. This indicated that 3 partial pressure gradient under high carbonate alkalinity. Urea excretion rate increased significantly after 12-16 h and 20-24 h in 32 mmol/L carbonate alkalinity water and 16-48 h in 64 mmol/L carbonate alkalinity water. The real-time PCR results showed that genes were up-regulated under carbonate alkalinity stress. The expression of in gills was significantly up-regulated after 12 h in 32 mmol/L carbonate alkalinity water, while was significantly up-regulated in gills after 6 h, 48 h, and 72 h and in kidneys at 6 h in 64 mmol/L carbonate alkalinity water. expression in gills was significantly up-regulated after 6 h in the 64 mmol/L carbonate alkalinity group. These results revealed that although ammonia excretion was inhibited in highly alkaline environments, and expression, recovering ammonia excretion, and excreting more urea. This study provided evidence of the nitrogenous waste excretion mechanism in in high alkaline environments. We speculate that the special mechanism of nitrogenous waste excretion facilitate the adaptation of to highly alkaline environments. Nonetheless, these findings raise more questions than answers, and further studies are needed to clarify the distribution and expression level of Rh protein in cells and tissues.

Abstract:The Pacific oyster () inhabits the intertidal zone and shows tolerance to air exposure conditions. Most marine invertebrates have been demonstrated to suffer large-scale mortality following sudden changes in osmolality, causing huge economic losses to commercial aquaculture. To explore the effect of air exposure on the genomic DNA methylation of marine shellfish, methylation polymorphisms in genomic DNA in the Pacific oyster were analyzed using the fluorescence-labeled methylation sensitive amplified polymorphism (F-MSAP) technique. The oysters were exposed to air individually for 0 d, 0.5 d, 1 d, 3 d, 5 d, 7 d, 9 d, and 11 d. The incidence of DNA methylation in adductor and gill tissue was 29.76% and 29.82%, respectively, in the control group (day 0). Compared with the control group, the level of total methylation in various groups under air exposure increased initially, after which it decreased. The total level of methylation on days 0.5, 1, 3, 5, 7, 9, and 11 was 36.59%, 38.86%, 43.02%, 39.30%, 51.13%, 46.79%, and 35.06%, respectively, in adductor tissues and 39.3%, 42.13%, 39.36%, 43.54%, 56.19%, 38.57%, and 28.99%, respectively, in gill tissues. The methylation level on day 7 was higher than that following other air exposure durations (<0.05); at the end of the experiment (11 d), the methylation level nearly returned to that of the control. Moreover, data regarding genomic DNA methylation mutation patterns at CCGG sites were not consistent with cytosine methylation patterns and patterns of variation between adductor and gill tissue; hypermethylation sites were more numerous than demethylation sites (<0.05), indicating that remarkable changes occurred in the hypermethylation sites of the Pacific oyster. The results of the present study implied that the alteration of methylation patterns in in response to air exposure might be strongly linked to stress resistance. These studies are fundamental to direct further research regarding DNA methylation in the aquatic shellfish epigenome, specific gene expression, and stress tolerance.

Abstract:In this study, two scallops, , were used to investigate the possibility of intergeneric distant hybridization in scallops. Using as male parent, we established four experimental groups-an orthogonal group MH, a reciprocal group HM, an inbred group HH-to investigate the fertilization, early development, and growth and survival of reciprocal crosses between the two scallops. The results show that reciprocal crosses of can derive hybrids. For reciprocal cross groups MH and HM, the time required for the embryos to develop into D-shaped larva was less than that required for embryos in the inbred groups MM and HH (MH 18 h, HM 19 h, MM 21 h, and HH 22 h). The average fertilization rate and average hatching rate of the MH and HM groups were lower than those of the MM and HH groups. Under different temperature, salinity, and sperm concentration, the fertilization rate and hatching rate of reciprocal cross groups MH and HM were lower than those of the MM and HH groups. A comparison of the growth of planktonic larvae among four experimental groups from day 2 to day 11 revealed that the shell length and height of the MH and HM groups were significantly higher than those of the MM and HH groups, with both showing obvious heterosis (<0.01). Experiments designed to predict the larvae of the orthogonal and reciprocal groups on the basis of the inbred group in shell length and height revealed that the growth tendency of hybrid scallop can be predicted using the BP neural network model method, and the error rate of the predicted values was less than 4%.

Abstract:Linear Mixed Effects Model and Restricted Maximum Likelihood (REML) were applied to estimate the genetic parameters for growth traits based on sixty-eight full-sib families of the Kuruma shrimp Penaeus . The results indicated that the heritability estimates of body length (BL), abdorminal segment length (ASL), and body weight (BW) were 0.1545±0.0505, 0.1672±0.0473, and 0.1934±0.0439, respectively, on day 45. On day 75, the heritability estimates were 0.1933±0.0475 for body length, 0.1937±0.0468 for abdorminal segment length, and 0.1992±0.037 for body weight, all of which were found to be at moderate levels. Strong positive phenotypic and genetic correlations between growth-related traits at different stages were detected. The phenotypic correlations between BL and ASL, BL and BW, and ASL and BW on day 45 were 0.7121±0.0188, 0.5147±0.0277, and 0.5052±0.0280, respectively, while the genetic correlations were 0.9896±0.0034, 0.9304±0.0321, and 0.9429±0.0301, respectively. The phenotypic correlations between BL and ASL, BL and BW, and ASL and BW on day 75 were 0.6710±0.0236, 0.6555±0.0181, and 0.6534±0.0160, respectively, while the genetic correlations were 0.7637±0.0161, 0.7479±0.0148, and 0.7177±0.0131, respectively. Selection for growth traits in was found to be effective in the present study, and selection for one growth trait can improve other growth traits simultaneously in a breeding program. The results of this study provided reference data for early selective breeding and multi-trait selection of .

Abstract:is a shell-less pulmonate and lives in the middle and high intertidal zone. It is considered as a commercially important species owing to its high nutritive value and beneficial effects in Chinese medicine. is also regarded as an important representative species for a better understanding of the evolution from aquatic to terrestrial life since this species has two methods of respiration-epidermal respiration and pulmonary respiration. Epidermal respiration plays an important role in the underwater life stageor stationary stage of , while pulmonary respiration contributes to its creeping or terrestrial life stage. In the present study, the effect of body size, water temperature (15℃, 20℃, 25℃, and 30℃), salinity (5, 15, 25, 35, and 45) and pH (7.5, 7.8, 8.1, and 8.4) on underwater oxygen consumption rate (OCR) and epidermal histology was determined to provide valuable information for understanding the respiratory mechanism of and its evolutionary characteristics. These results demonstrated that smaller had higher underwater OCR than larger individuals. Epidermal respiration differed significantly at various temperatures, salinities, and pH values (<0.05). The OCR and the inner and outer diameter of the mucus gland increased as water temperature increased below 25℃. The highest values were observed at 25℃ and then began to decrease gradually at temperature above 25℃. The thickness of the dermis decreased with increasing temperature. The number and the inner and outer diameter of the granular gland did not differ considerably between temperature groups. The differences with respect to salinity in dermis thickness and inner and outer diameter of the mucus gland/granular gland were the same as those with respect to temperature. The highest values were observed at salinity 25. The pH also had a significant effect on respiration. The OCR and inner and outer diameter of the mucus gland increased with pH, while dermis thickness and inner and outer diameter of the granular gland decreased. The number of granular glands first increased and then decreased; peak values were observed at a pH of 8.1. However, respiration levels decreased with time in all groups. In conclusion, environmental factors such as temperature, salinity, and pH had significant effects on underwater epidermal respiration. Items such as dermis thickness and the inner and outer diameter of the granular gland play more important roles in epidermal respiration in than the granular gland, which may be key to keeping the body wet and protecting it from invasion or damage from its habitats. showed optimum respiration metabolism in water at a temperature of 25℃, salinity 25, and pH 8.1. At lower temperature (15℃), higher salinity (45 psu), and lower pH (pH 7.5), this organism will be under considerable stress. This might be related with to the factors associated with its optimal living conditions. The results of this study will provide basic information for the protection and aquaculture of this species and will also be helpful to understand the evolution from aquatic to terrestrial life.

Abstract:Lymphocystis disease is a viral infection caused by lymphocystis disease virus, which has serious impacts on the aquaculture industry, resulting in heavy losses. In order to select new varieties of Japanese flounder () resistant to lymphocystis disease, eight experimental groups and one control group were established in 2015. The exposure experiment was conducted on one farm with high incidence of lymphocystis disease, and the protection rate of each group was determined. At the same time, the growth traits of each group at 120 d, 180 d, 240 d, and 300 d were measured and compared. The results showed that there were different growth patterns for each group in different periods, showing inconsistent growth patterns among groups. However, in all the groups, the growth performance of group G2 was always ranked the highest for each period. The results also showed that the disease resistance protection rate of the control group was only 59.57%, while the disease resistance protection rate of all the tested groups was above 60%, reaching up to 97.20% for group G2. From the overall analysis, there were no significant differences in the body weight and body length between the disease resistant or sensitive individuals at 390 d of age. The body weight and body length were positively correlated with disease resistance protection rate, while their effects were not significant (>0.05). However, the mean body weight of disease-resistant individuals in group G2 was significantly higher than that of disease-sensitive individuals (<0.05). Based on the group G2, it is expected that a new variety of fast-growing lymphocystis disease-resistant Japanese flounder could be developed.

Abstract:belongs to Bangiaceae, Bangiales, Protoflorideae, Rhodophyta. For its high commercial and nutritional value, it becomes one of the most important seaweed cultivars in the coastal area of northern China. For decades, because of incorrect breed conservation and inbreeding, the germplasm of this species had been serious degenerated, which resulted in a decline of yield and quality such as slower growth rate, thicker, matured earlier and more susceptible. These problems seriously affected the economic benefits of the cultivation. Therefore, breeding new varieties of is greatly significant for the sustainable development of this industry. In order to select a new variety of with faster growth rate, higher quality and wild-type color, intraspecific hybridization of the green-type pigmentation mutant and red-type pigmentation mutant in was conducted to isolate an improved strain (LC-14) from the recombinants. After cultured for 70 days, the mean length and wet weight of F₁ blades in LC-14 strain was 106.53 cm and 3.07 g, which was 4.39 and 10.27 times of the wild-type strain (WT), respectively. The results indicated that the improved strain had higher growth advantages, and the higher yield compared with WT strain. Being cultured to 55 days, the contents of three major photosynthetic pigments (chlorophyll a, phycocyanin and phycocyanin) in LC-14 strain were 9.85 mg/g, 52.09 mg/g and 23.26 mg/g, with an increasing by 65%, 65% and 49% when compared with WT strain respectively. Meanwhile, the thickness of blades of LC-14 strain was 20.89 μm, which is 32% thinner than that of WT strain. These results showed that the taste was better, and the quality was higher than those of the WT strain. In addition, the daily amount of conchospores released from LC-14 strain could be more than 2 million and the total amount of conchospores for successive 20 days was 761.32×10⁴, which was 1.28 times compared to WT strain. The results showed that conchospores released were sufficient during the stage of seedlings collection and the productive requirements of releasing amount could be fully satisfied. In summary, all of these results above confirmed that LC-14 strain with fast growth rate, high quality, large amount of conchospores and similar color with wild-type was suitable for cultivation, which completely achieved the original intention of this study. Therefore, LC-14 strain is expected to become a new improved variety through the national approval and be applied in the practical production in the near future.

Abstract:Probiotic dietary supplementation has been widely used and has positive effects on the growth performance and host health of different fish species. Little attention is paid to its influence on fish gastrointestinal mucosal microbiota. A feeding trial was conducted to investigate the potential effects of probiotic compounds of on the growth performance and gastric and intestinal mucosal microbiota of rainbow trout. A total of 360 rainbow trout with average body weight of (205.1±4.82) g were distributed in four equal groups in three replicates, and received one of the following experimental diets for 42 days:basal diet, basal diet supplemented with 5×10⁶/5×10⁷ CFU/g (T1, see tables 1 and 2), 1.5×10⁷/1.5×10⁸ CFU/g (T3, see tables 1 and 2), and 2.5×10⁷/2.5×10⁸ CFU/g (T5, see tables 1 and 2) of probiotic compounds. Significant improvement in weight gain ratio, feed conversion ratio, and the specific growth rate (SGR) was found in T1 diet supplemented with probiotic compounds. Significantly decreased mortality was found in T1 and T3 diets. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) was applied to compare the gastrointestinal mucosal microbiota of different treatments. In gastric mucosa, 35.7±17.0 (C0), 37.0±3.5 (T1), 36.7±13.6 (T3), and 26.0±13.2 (T5) bands were found, with no significant differences (=0.692). In intestinal mucosa, 23.3±5.8 (C0), 22.3±3.2 (T1), 16.7±8.0 (T3), and 24.7±7.4 (T5) bands were found, also with no significant differences (=0.475). The bacterial diversity of gastric mucosa increased with increasing probiotic concentration, but it decreased in T5. However, the bacterial diversity of intestinal mucosa decreased with increasing probiotic concentration, which showed recovery in T5. Using both the unweighted pair-group method with arithmetic means (UPGMA) clustering and principal component analysis (PCA) ordination, we found that the microbial community structures of gastric mucosa and intestinal mucosa were different. No significant influences were found on bacterial diversity and microbial community structure of intestinal mucosa of rainbow trout with addition of probiotic compounds of . The potential risks of high concentrations of probiotics should be paid more attention.

Abstract:Nitrogen accumulation is one of the major causes of water pollution and eutrophication in aquaculture. Excessive amounts of the toxic forms of nitrogen (ammonia and nitrite) have a considerable effect on the survival and growth of aquatic organisms and thus lead to huge economic loss in aquaculture. Biological nitrogen removal technology is an efficient process for nitrogen removal from water in aquatic habitats, wherein probiotic bacteria convert nitrite-N into nitrate nitrogen (nitrate-N) or nitrogen gas. Moreover, owing to lower energy consumption and operation cost, this technology is commonly used in aquaculture. Many studies have used several kinds of bacteria to reduce the toxic effects of nitrogen and demonstrated an improvement in water quality. The present study aimed to identify bacteria that efficiently removed nitrite nitrogen and ammonia nitrogen. The strain O-11 was isolated from shrimp culture water after enrichment culture and had removal efficiency for nitrite nitrogen and ammonia nitrogen of 96.17% and 88.27%, respectively, in 24 h. Molecular biological and physiological and biochemical identification revealed that the strain was closely related to . The isolated strain O-11removed nitrite nitrogen more efficiently when the temperature ranged from 20℃ to 30℃, while ammonia nitrogen removal was better when the temperature ranged from 20℃ to 35℃. The nitrite nitrogen removal ability of the isolated strain was stable when salinity was less than 30, while the ammonia nitrogen removal ability was considerably higher in alkaline conditions. A safety assessment revealed that the strain O-11 was safe for when the initial bacterial concentration ranged from 10⁵ to 10⁸ cfu/mL. The survival rate and growth rate of experimental significantly increased when the initial bacteria concentration was 10⁵ cfu/mL. These results demonstrated great potential value of the isolated strain O-11 as a suitable candidate for the removal of harmful forms of nitrogen from aquaculture water.

Abstract:In this study, we investigated the impact of Hg²⁺ and Pb²⁺ on the growth and photosynthetic physiological characteristics of by exposing algal thalli to five concentrations of HgCl2 (0.01 mg/L, 0.025 mg/L, 0.05 mg/L, 0.1 mg/L, 0.25 mg/L, and 0.5 mg/L) and PbCl2 (0.05 mg/L, 0.1 mg/L, 0.5 mg/L, 1.0 mg/L, 2.0 mg/L, and 4.0 mg/L); the reference group exposed to seawater without Hg²⁺ and Pb²⁺. The growth rate, photosynthetic rate, pigment content, chlorophyll Ⅱ fluorescence characteristics, and the activity of RuBisCO and PPDK in the thalli were measured after 7 days of incubation. The special growth rate (SGR) reduced significantly as the Hg²⁺ level increased (<0.05), mortality was observed following incubation with the highest concentration of Hg²⁺, and the photosynthetic rate reduced by 35.48%-77.50%. Similar trends were also observed for chlorophyll a (Chla) and carotenoid (Car) levels (<0.05). Phycoerythrin (PE) and phycocyanin (PC) content was significantly lower at Hg²⁺ levels above 0.1 mg/L (m and Y(Ⅱ) with Hg²⁺ concentration was close to a bimodal curve, and the second peak appeared at 0.05 mg/L;PPDK activity showed a similar trend. The specific growth rate and Chla and Car content was significantly lower at Pb²⁺ levels above 1 mg/L (<0.05). However, no significant change in either chlorophyll Ⅱ fluorescence characteristics or the level in PC content was found among different Pb²⁺ levels. Significantly lower RuBisCO activity was found at the highest Pb²⁺concentration than at lower concentrations, while PPDK activity was significantly higher ( both showed detrimental effects on the growth and photosynthesis of . A stress response was observed after the Hg²⁺concentration reached 0.01 mg/L, and this response increased as Hg²⁺concentration increased, while no stress response was observed at Pb²⁺ concentrations below 1 mg/L.

Abstract:is an excellent unicellular bait for the larvae of many aquaculture animals. Thus, screening for strains with rapid growth rate and high content of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) is very important for the breeding of aquaculture animals. However, most of the strains in China have been derived from a common ancestor called have been developed after a long duration of geographical isolation. Whether the traits of these strains have changed or not remains unknown. In order to evaluate the status of the phenotypic traits of different geographic isolates for future selective breeding, comparative analysis of five strains of (FACHB-861, OA3011-QD, OA3011-LK, OA3011-AY, and OA3011-LZ) with regard to their taxonomy, growth, and fatty acid composition was conducted. Different strains were cultured under identical conditions for six days until they reached a stationary phase. Genomic DNA was extracted for polymerase chain reaction sequencing of the 18S rDNA gene. The OD₆₆₀ was recorded daily for plotting a growth curve. When the cultures reached stationary phase, they were harvested by high-speed centrifugation for biomass determination and fatty acid analysis by using gas chromatography. Phylogenetic analysis of the 18S rDNA gene suggested that FACHB-861 was distantly related with the OA-3011 strains. OA3011-LK, OA3011-AY, and OA3011-LZ had identical 18S rDNA sequences, but the 18S rDNA sequence of OA3011-QD differed from that of the other OA-3011 strains at one position, resulting in a single base substitution. The growth curve showed that the five strains reached stationary phase at different times. FACHB-861 showed a distinct pattern of growth, unlike the other four OA-3011 strains. The final biomass concentrations were significantly different between FACHB-861 and OA-3011 strains as well as among OA3011-LK, OA3011-AY, and OA3011-LZ (<0.05), whereas the growth rates were not significantly different among the strains (>0.05). The total fatty acid content of FACHB-861 and OA3011-LZ were significantly lower than that of OA3011-LK, OA3011-QD, and OA3011-AY (<0.05). The fatty acid profile of FACHB-861 was remarkably different from that of the OA-3011 strains. However, a conspicuous variation in fatty acid compositions was also observed among OA-3011 strains, indicating a wide and frequent quantitative phenotypic variation among the strains of . These variations resulting from geographic isolation might provide a feasible method for the selective breeding of strains. According to the screening criteria such as growth rate or DHA, EPA, and polyunsaturated fatty acid content, our preliminary analysis showed that OA3011-LK, which has the highest growth rate, and OA3011-QD, which contains the highest amount of DHA, are promising candidates for further screening.

Abstract:Chlorophyll fluorescence technique can provide an accurate, quick, and non-destructive assessment of the efficiency of photochemical conversion. One of the most commonly used fluorescence parameters is the maximal quantum yield of photosystem Ⅱ (PSⅡ) (), which has been shown to be a sensitive indicator of photoinhibition. Moreover, other fluorescence parameters, such as the effective quantum yield of PSⅡ (yield), the relative electron transport rate (rETR), photochemical quenching (qP), non-photochemical quenching (NPQ), the initial slope of rapid light curve (), and the minimum saturating irradiance (I_k), are also important in investigating photosynthesis. As such, chlorophyll fluorescence has become an increasingly powerful tool and widely used technique to study photosynthesis in marine algae. Caulerpa lentillifera is a tropical macroalga that grows mainly in Okinawa, Malaysia, the Philippines, Vietnam, and other places. is a potential healthy food with high nutritional value that contains a variety of essential amino acids, vitamins, mineral elements, and unsaturated fatty acids. In addition, also contains caulerpenynes, polysaccharides, and other physiologically active substances. It has beneficial effects for type Ⅱ diabetes and cancer. belongs to the marine benthic green algae, which are very sensitive to high light intensity. Light intensity reportedly has a significant effect on the growth of , but the effect of different light intensities on the photosynthesis process of is still unknown. Therefore, there is a need to better understand the photosynthetic characteristics of by investigating the effects thereon of different light intensities. In this study, the chlorophyll fluorescence characteristics of were investigated with MINI-PAM chlorophyll fluorometer under the light intensities of 10 μmol/(m²·s), 120 μmol/(m²·s), and 360 μmol/(m²·s). From 10 μmol/(m²·s) to 360 μmol/(m²·s), the maximal quantum yield of PSⅡ, the effective quantum yield of PSⅡ, the relative electron transport rate, and the initial slope of rapid light curve of all decreased with increasing light intensities. The samples treated with light intensities of 120 μmol/(m²·s) and 360 μmol/(m²·s) had higher photochemical quenching and lower non-photochemical quenching than those treated with 10 μmol/(m²·s). The minimum saturating irradiance increased dramatically and the maximum relative electron transport rate decreased sharply in ·s), but both were significantly higher under the light intensity of 120 μmol/(m²·s) than that in samples exposed to the light intensity of 10 μmol/(m²·s) for 4 h and 8 h. The minimum saturating irradiance and the maximum relative electron transport rate was substantially lower in ·s) from 8 h to 12 h. These results suggest that is a kind of seaweed adapted to a low light intensity of 10 μmol/(m²·s), and that it could im-prove light tolerance in different ways under high light intensities of 120 μmol/(m²·s) and 360 μmol/(m²·s), but light intensity of 360 μmol/(m²·s) for up to 12 h could cause photo-oxidation and damage its photosynthetic structure.

Abstract:Seagrass beds are highly productive ecosystems that provide essential habitat and food for various marine species. However, seagrasses have been declining worldwide for decades because of human activities and global climate change. The conservation and restoration of seagrasses has become extremely urgent, especially in China. Recent studies showed that, in the rhizosphere of seagrasses, the organic carbon exudates from plant residues and roots are an important carbon source for could provide nitrogen for the growth of the plants, thereby promoting the restoration of seagrasses. Therefore, investigating N₂ fixation by in the seagrass rhizosphere is essential since it might play an important role in the nitrogen cycle of the seagrass bed ecosystem. In this study, the growth-promoting activities of the rhizobacteria of eelgrass was investigated by isolating two nitrogen-fixing strains (3A and 4G) from the rhizosphere sediments of by using N-free medium. Based on the morphology, physiological and biochemical characteristics, sequence analysis of 16S rDNA, and the nitrogenase structural gene nifH, we identified the 3A bacterium as sp.. The optimal culture conditions for the two Rhizobium strains were established, and typical growth curves for the two trains were obtained. In particular, strain 3A was a gram-positive bacterium and had an orange yellow-colored circular colony. In addition, it used D-mannose, D-melezitose, and L-rhamnose as carbon sources. The optimal growth temperature, pH, and salinity of 3A were 31.49℃, 8.18, and 2.585%, respectively. In contrast, strain 4G was gram-negative bacteria and had milky circular colony. It could use a series of hydrocarbons as carbon sources, such as D-cellobiose, D-glucose, D-maltose, sucrose, D-mannitol, and D-trehalose. Its optimal growth temperature, pH, and salinity were 37.27℃, 7.99, and 2.920%, respectively. Previous studies have shown that sp. can promote seagrass growth and increase the content of carotene, soluble sugar, and other substances, indicating that this species is a kind of growth-promoting bacteria. Nitrogen-fixing sp. is a typical plant growth-promoting bacterium with strong stress resistance that can produce beneficial plant growth-promoting and antibacterial substances. The nitrogen fixation rates of 3A and 4G were 252.21 nmol C₂H₄/(mL·h) and 196.31 nmol C₂H₄/(mL·h), as revealed by the acetylene reduction method. Comparison with the nitrogen-fixing bacteria reported in other studies revealed that the two strains isolated in this study showed good nitrogen fixation ability. Under suitable growth conditions, the two bacterial strains exhibited logarithmic phase proliferation. Accurate positioning of the bacterial growth logarithmic phase and elucidating the growth characteristics of the bacterial strains could provide basic data for the production of bacterial fertilizers in the future. The bacterial strains obtained in this study might be applied in the future development and application of microbial inoculants and seagrass Z. marina beds in the future.

Abstract:Heavy metal pollution in food is one of the major problems affecting food safety. Cadmium is a kind of heavy metal that is non-essential, highly toxic, and easily accumulated. It enters the food chain and poisons animals and humans. Shellfish easily accumulate heavy metals because of their low metabolic rate. Scallops can accumulate high amounts of cadmium, especially compared to other shellfish, and the content of cadmium in the edible part of scallops was several times higher than that considered the national standard; hence, this has become the focus of attention. In order to understand the molecular mechanisms of high accumulation of cadmium, this study was designed to obtain transcript sequence data and assess gene expression in the digestive gland of the scallop exposed to cadmium by using molecular technology. In all, 105071 unigenes were obtained with an average size of 829 bp and a N50 length of 1573 bp. All the predicted protein sequences (unigene sequences were translated using the Transeq program of the EMBOSS suite) were searched against the NR and Swiss-Prot protein sequence databases for gene annotation. Further, 24493 unigenes were assigned to at least one GO term under one of the three categories:biological process, cellular component, and molecular function. A total of 12028 unigenes were classified functionally into 26 KOG families, including biochemical metabolism, signal transduction mechanism, defense system, cellular structure, and gene expression. Moreover, 7849 unigenes were assigned to different KEGG pathways. The most represented pathways were signal transduction (1349 members), carbohydrate metabolism (751 members), and transport and catabolism (563 members). Most of them were involved in biological progress, e.g., ATP-binding cassette transporters, oxidative phosphorylation, ribosome biogenesis in eukaryotes, MAPK signaling pathway, glutathione metabolism, serine and threonine metabolism, and steroid hormone biosynthesis. These data would provide potential molecular targets in bivalves exposed to marine pollutants for functional studies of genes and to better understand the molecular mechanisms involved in metabolic and immune pathways.

Abstract:The aim of this study was to investigate the safety of the consumption of scallops exposed to diesel pollution, so as to provide basic information for the evaluation of the effects of oil pollution on the food safety of marine shellfish. The accumulation and elimination characteristics of scallops () to diesel were explored using the semi-static dynamic test in the present study. Scallops were exposed to light (-10^#) and heavy diesel. After a certain period of time, the scallops were placed in uncontaminated seawater. The content of petroleum hydrocarbon, polycyclic aromatic hydrocarbons (PAHs), and polycyclic aromatic sulfur heterocycles (PASHs), as well as alkanes, in water and scallop tissue at different times was determined by gas chromatography mass spectrometry. The results obtained are as follows:The content of petroleum hydrocarbon, PAHs and PASHs, as well as alkanes, in the scallop tissue was positively associated with the accumulation time and the petroleum hydrocarbon concentrations in water. Different tissues accumulated diesel to differing extents with accumulation being higher in the viscera than in the mantle and higher in the gills and other organs than in the adductor muscle. The accumulation ability of diesels in scallops was also related to the type of diesel. Under the same conditions, the scallop accumulated more heavy diesel than light diesel, while they eliminated heavy diesel more slowly than light diesel. Thus, heavy diesel pollution is more harmful to the quality and safety of shellfish and deserves more attention. When placed in uncontaminated water, the contaminated scallops could gradually eliminate petroleum hydrocarbons accumulated in the body, but the elimination was slower than the accumulation. The bioconcentration factor of alkane was lower than that of PAHs, and alkane in scallops was therefore eliminated faster than PAHs were. However, alkane is the main component of diesels. Thus, the elimination of petroleum hydrocarbon by scallops was mainly because of the elimination of alkane. The low-molecular-weight PAHs (comprising 2-3 aromatic rings) were dominant in the PAHs of contaminated scallops, and they were eliminated faster than high-molecular-weight PAHs (comprising 4-7 aromatic rings). When the contaminated scallops were placed in clean water, the petroleum hydrocarbons residue in the scallops returned to normal levels in a short time, but PAH residues (especially with four or more aromatic rings) remained for a long time. On the basis of the above results, we suggest that petroleum hydrocarbons in shellfish be monitored along with that in the water after an oil spill, and the PAHs residue also be taken into consideration. In addition, in the interest of food safety, the viscera of scallops should be discarded.

Abstract:The Japanese anchovy is a dominant species in the food web of the Yellow Sea, China. It is not only a small pelagic zooplankton feeder, but also the prey for over 30 important higher trophic level species. Its population plays a crucial role as wasp-waist control functional group in the marine ecosystem in the Yellow Sea. In traditional ecological research, the diets of the anchovy were determined based on species analysis of the gut content or stable isotope, fatty acid analysis. In this study, the application of particle size in the food analysis of fishes was advanced by analyzing the prey size compositions of anchovy in relation to the fish species body size. Data for species and size classification of prey in the anchovy gut content were collected, and zooplankton sorting was performed between June 2000 and November 2014 in the southern part of the Yellow Sea. The anchovy body size (standard length) ranged from 10 mm to 150 mm. Results showed that the species composition of anchovy diet was mostly determined by the environmental living conditions. Most zooplankton species in the diets of anchovy could be found in the environmental waters. The species and size diversity of diets varied similarly along with the anchovy body size. Both diversity indices of species and particle size had the highest values at the anchovy body size class of 110 mm. The mean size of prey particles increased gradually with anchovy body size. Larger anchovy tended to prey on relatively bigger items. According to the prey selectivity, three prey size shifts were found for the anchovy with body size: ≤ 30 mm, 30-70 mm, and ≥ 70 mm. Thus, integrating particle size into anchovy prey analysis could be useful for the evaluation of feeding selectivity in the fish feeding ecology analysis.

Abstract:The Administrative Department of Fisheries and Researchers has focused almost exclusively on the in-dustrialized fishing sector. Nevertheless, small-scale fisheries account for more than 90% of the world's capture fisheries and fish workers. Thus, complete understanding of the dynamics of small-scale fisheries and exploring the factors that drive fishery activity are urgently needed. Many multivariate methods have been applied to small-scale fishery data in order to distinguish the factors that influence catch composition. This study used multivariate methods to evaluate the spatial variations of catch composition and analyzed the relationships between environmental/fishing factors and catch composition. The survey data from 2013 to 2015 were obtained from 3 stations in Haizhou Bay where stow nets are used. In all, 103 species were captured. We selected 23 species whose weight was more than 1% of all catch species, to analyze the factors that influenced the catch composition. The 23 catch species accounted for 85.79% of the total weight. Cluster analysis (CA) was used to assess the catch species composition, and the CA dendrogram showed two groups, which were significant at the 95% confidence interval (<0.05). Approximately 15 catch species were included in the first cluster and 8 in the second cluster. According to the results of similarity percentage analysis, Alpheus heterocarpus were the main contributors to the similarity between the samples of the first cluster, and their similarity contribution rates were 26.68%, 16.86%, and 11.01%, respectively. The second cluster was represented by Odontamblyopus rubicundus, and their similarity contribution rates were 41.74%, 18.50%, and 17.13%, respectively. Further, the two clusters were distinguished from each other by , and their variance contributions were 11.87% and 10.28%, respectively. The non-metric multidimensional scaling (NMDS) discriminated stations, years, and months with respect to species catch composition. Both NMDS plots and one-way analysis of similarities indicated that catch species composition changed significantly among different stations and different months (>0.05). The redundancy analysis (RDA) suggested that environmental and fishing factors had significant effects on catch species composition. These variables jointly explained 54.11% of the total variance of the selected species. Among the fishing factors, effective net was the most important factor that explained 67.49% of the total variance, and the daily catch explained 32.51% of the variance. Among the environmental factors, sea surface temperature was the most important factor that explained 27.74% of the total variance, followed by land distance (18.43%), chlorophyll-a content (16.22%), sea surface salinity (13.78%), and wind speed (13.68%); depth only explained 10.15% of the total variance. Effective net was the most important factors driving catch species composition in the first cluster. In contrast, catch composition of the second cluster was influenced by sea surface temperature and wind speed. The partial RDA that included only environmental variables explained 26.40% of the variance, showing that environmental factors explained a significant proportion of the variation in catch species composition. Approximately 8.18% of the variance was explained by the removal of environmental variables. For example, in the second cluster showed a positive relationship with daily catch, and showed a positive relationship with sea surface temperature, whereas had no significant association with any of the variables. Catch composition of stow nets installed at Haizhou Bay varied temporally and spatially and was influenced by the combined effects of a range of environmental and fishing factors. Identifying factors influencing small-scale fisheries could be a critical step to implement marine fishery management measures that are more likely to succeed.

Abstract:Fishery resource density is a key indicator for assessing resource status and is commonly estimated using bottom trawl survey data. Because of the non-uniform distribution of marine organisms, bottom trawl data always contain extreme values (zeros or very large values), which will affect the accuracy and precision of the estimate of resource density. In order to decrease the effect of extreme values on the estimation of resource density, the △-distribution model was used when analyzing trawl survey data for in the Yellow River estuary between 2013 and 2014.The estimate of the mean resources density using the model-based method and that using the designed-based method was compared, and the effect of the quantity and distribution of survey data on the results for the △-distribution model method was also discussed. With respect to survey data for in August and October, the density estimated using the model-based method was lower than that using the design-based method, while the densities estimated using the model-based method were higher than those using the design-based method for other data sets. The quantity and distribution characteristics of survey data might be important factors affecting assessment results using the △-distribution model. Variance estimated using the model-based method was much less than that estimated using the design-based method for all data for the two species in different months. Zero and maximum-value data had different effects on the estimation of resource density using the △-distribution model method; the model was robust when dealing with survey data with high stability and precision.

Abstract:As one of the most important inshore fishery waters, the Beibu Gulf, is attracting increasing attention with regard to the density of fishery resources and resource changes. The fishery acoustic technology is increasingly being applied for fishery resource assessment, because of its advantages such as rapid, continuous, greater sampling rate, and rich spatio-temporal data. Nonetheless, this technology is influenced by some factors such as weather, sea conditions, and survey route; hence, the echo data is unreliable. In order to overcome the possible defects that exist in the sampling process, and to obtain a more reasonable density distribution of fishery resources, we combined the spatial interpolation methods with the fishery acoustic technology. We conducted a preliminary analysis of the Beibu Gulf fishery acoustic survey data obtained during July to August of 2014 by using Echoview (a fishery acoustic survey data processing system, Version 6.1). Next, Inverse Distance Weighted (IDW), Ordinary Kriging (OK), and Simple Kriging (SK) were applied to analyze the actual data after logarithmic transformation of the practical detection data, in order to obtain normally distributed data. By calculating and comparing the determination coefficients (), mean error (ME), and root mean square error (RMSE) of the three interpolation models (IDW, OK, and SK), we selected the optimal interpolation model fitting the fishery acoustic survey on the Beibu Gulf. The results showed that the distribution of fish density was relatively uniform, which indicated relatively less concentrated distribution in the survey area. Further, fish were mainly concentrated in the mideast coastal area and the midwestern region of the common fishing zone. In contrast, the distribution of fish in the south-central offshore waters was rare. By comparing the three interpolation parameters, we found that and RMSE showed a good precedence similarity in the following order:OK > SK > IDW. In contrast, ME showed the order of OK > IDW > SK. Our findings suggest that OK could be a better predictor of resource density distribution of the Beibu Gulf waters for the evaluation of fishery acoustic resource density of the area and is useful for potential application in the combination analysis of fishery acoustic technology and spatial interpolation.

Abstract:The coastal waters along the southern Shandong Peninsula waters are rich in fishery resources, and the spawning and feeding grounds for many important economic marine organisms are located here. In recent years, overfishing and pollution have caused considerable damage to fishery resources here, and crabs, including important economic species (such as ) and bait-type species (such as ) have been adversely affected. Although the community structure and diversity of crabs are of great significance for fishery production and fishery ecology, little research has been conducted in this respect in the southern Shandong Peninsula waters. Based on data from four bottom trawl surveys in this area from 2014 to 2015, the spatial and temporal distribution, structure community, dominant species, and diversity of crab populations were analyzed. Fifteen species of crabs were caught during the four surveys, which belonged to 7 families and 12 genera. The number of species caught changed seasonally because, as the area is located in the warm temperate zone, its temperature changes seasonally and the migratory crabs migrate to and from this area seasonally as well. were the main economic species caught, and the others were low-value species. Because of the reduction in the number of natural enemies, the euryhaline was the dominant species in all four surveys. Biomass changed seasonally, with the highest biomass observed in summer and the lowest in winter. Except in autumn, distribution of biomass differed regionally owing to the migration and foraging of . According to the data, the range of the Shannon-Wiener diversity index (') was 0.23-0.37, and that of the Margalef richness index () was 0.32-0.55. The diversity index changed seasonally, indicating an unstable community structure and lower-level diversity of crab populations in this area. The diversity index was higher in the east, lower in the west, and higher in the near shore, and lower in the offshore; therefore, we conclude that the eastern offshore area along the southern Shandong Peninsula is suitable for crab growth. The results of a CLUSTER analysis showed that the crab species in every season in the coastal waters along the southern Shandong Peninsula could be divided into three groups:the southwestern waters group, the northeast waters group, and the northwest waters group. The populations in every group changed with season and the community structure was unstable. The key factor that influenced groups division was the presence of small bait-type species, such as , because the populations of the large economic species are facing considerable damage due to overfishing and environmental pollution. This study shows that:1) Mostcrabs in the coastal waters along the southern Shandong Peninsula were small, bait-type species. The crab diversity was very low, and the dominant species varied considerably. 2) The community structure of crabs in the coastal waters along the southern Shandong Peninsula can be divided into three parts; most of the crabs found in this area are small bait-type crabs.

Abstract:The vertical habitat of tuna has significant effects on the longline catch rates, which are primarily influenced by oceanographic features. In order to support longline operations and fishery management, several key environmental factors were used to evaluate the influence of vertical habitat on longline catch rates in the tropical Atlantic Ocean. Regression model was used to determine the relationship between environment and longline catch rates, expressed as catch per unit fishing effort (CPUE), while generalized additive model (GAM) was used to evaluate the significance of environmental factors on CPUE. The results revealed that the environment and spatio-temporal factors had significant effects on catch rates, and the relationships were nonlinear. High catch rates were achieved in the summer and winter to the north of the equator, between 30°-50°W. The shape of the 12℃ isolines (open para curves) showed influences on longline catch rates. High catch rates were observed where the depth was lower than 250 m. The hooking rates declined as the depth of 12℃ isolines increased to 400 m. The nonlinear effects of the low depths of thermoclines and relative depths were both like a dome. The longline catch rates increased as the thermocline depth and relative depth increased to 200 m, while at depths greater than 200 m, the catch rates decreased. There were strong relationships between longline catch rates and the thermocline depth and relative depth, which were 200 m and 50 m, respectively. These results suggest that the influences of 12℃ isolines and thermoclines were cross. The catch rates reached maximum levels when the vertical habitat was compressed consistent with hooking depth and decreased when the vertical habitat depth was too large or too small, but could change by adjusting the depth of hooks. The vertical habitat of tuna should be taken into account in fisheries stock assessments and fishing grounds analyses.

Abstract:Based on the on-sea measurements on net position and net mouth height (vertical opening) of the 400 m×143.44 m (headline 61 m) of Antarctic krill trawl used by the "Mingkai" krill trawler operated at South Shetland Island from February to July 2015, this paper analyzed the effects of towing speed and warp length on the net position and net mouth height. The net position and net mouth height were measured by DR-1050 depth instruments and the corresponding towing speed and warp length during trawling were also recorded. In this study, the net mouth height is defined as the difference in water depth between the headline and footrope, while the net position is defined as the water depth of the central position of the net mouth. According to the usual operation practice of the fishing vessel and characteristics of the krill aggregation, the range of warp length increased from 138 m to 258 m, with 20-m intervals, and tow speed increased from 1 kn to 3 kn with 0.5-kn intervals. The main results are as follow:(1) The net mouth height of the krill trawl studied ranged from 13.6 m to 24.1 m, while the net position ranged from 50 m to 70 m deep. (2) During trawling, net position was controlled mainly by the length of warp. For each additional 20 m from 138 m of the warp length, the net position decreased by 1.9 m on average, and the net mouth height reduced by approximately 1.1 m on average. Warp length showed significant effects on both the net position and net mouth height (<0.01). (3) When towing speed increased from 1.0 kn to 3.0 kn, average rise rate of the net position reached 2.9 m/kn with the variation of warp length changing from 138 m to 258 m. When towing speed increased from 1.0 kn to 3.0 kn, the vertical opening of net mouth average reduction rate reached 2 m/kn, accounting for 19.8% on average. Towing speed had a significant impact on the net position and net mouth opening (<0.05). (4) Analysis of the relationship between rate of net position change and towing speed expression showed that average rate of the net position change decreased first and then increased with different ranges of towing speed under different warp lengths. This result can not only provide useful reference for the Antarctic krill fishing vessel captain who can, according to the size or water layer of the krill aggregation and its relation with the location of the net, timely adjust the warp length and towing speed and control the net at the water depth for accurate fishing, but also provide basic information for Antarctic krill trawl model experiments and independent design of the Antarctic krill trawl net.

Abstract:To promote the development of Antarctic krill ( Dana) fishery, we proposed two designs of the 4-panel trawl (dh256-1 and dh256-2). The net mouth perimeter of the two trawls was the same, and the width ratio of belly panel to side panel (WRBS) was different:1.00 for dh256-1 and 1.10 for dh256-2. Model experiments were used to study trawl performance, and to determine the optimized nets and accessories, which include the sum of buoyance and sinker weight (SBSW), bridle length, and horizontal opening coefficient ( was between 0.5 and 0.6 or when the trawl speed was under 1.5 m/s and the <0.05) was noted in the vertical net opening between the two trawls:the vertical net opening of dh256-2 was remarkably faster than that for dh256-1. For improving the trawl performance, the SBSW should be larger for dh256-1:the minimum SBSW for dh256-1 was 4.59 tf and that for dh256-2 was 1.98 tf. These differences might be related to the flow attack angle of the nets. The WRBS of dh256-2 was larger than that of dh256-1; the flow attack angle and head surface of belly panels increased and improved the vertical net opening. Con-versely, when the WRBS was smaller, the flow attack angle and head surface of side panels increased, and the pull of side line to bridle was strengthened, thereby limiting the vertical net opening. Therefore, when the WRBS is smaller, the SBSW should be larger. No significant difference in coefficient of the energy consumption ( was inversely related to the _e; when the bridle length was ≥ 50 m, the effect of bridle length to both the trawls was not obvious. Therefore, 50 m bridle needs to be used for the two trawls. The effect of SBSW on the of dh256-1 was related to the trawl speed:when the speed was ≤ 1.5 m/s, the effect of SBSW on C_e declined remarkably with an increase in SBSW. Since the trawl speed of the Antarctic krill is usually around 1.5 m/s, the dh256-2 was recommended for Antarctic krill fishery. These results can provide a basis for designing Antarctic krill trawls.

Abstract:The Japanese flounder () is an economically important marine fish that has been widely cultured in Japan, Korea, and China. The growth rate of females is significantly higher than that of males; production of all-female Japanese flounder populations for aquaculture has considerable advantages for improving yield and economic benefit. Gynogenesis is a type of parthenogenesis whereby homologous or heterologous sperms penetrate into the eggs and trigger embryogenesis; however, the sperm nucleus does not fuse with an egg nucleus to form a zygote. Thus, gynogenetic individuals inherit only maternal genetic information. In this review, we introduce the recent progresses of artificial introduction of gynogenesis in Japanese flounder. First, we describe the methods of meiogynogesis and mitogynogenesis. Next, we review the applications of gynogenesis in Japanese flounder, such as sex control and production of clones. Finally, we propose a breeding system using gynogenesis and discuss its potential applications in the genetic improvement and breeding of new variations in fish.