Abstract:Since its introduction from Southeast Asia in the late 1980s, marble goby (Oxyeleotris marmorata) has been artificially bred and cultured in China over 3 decades, and has developed into an important and excellent aquatic fish species. With the fast expansion of the culture scale, the original varieties have been unable to meet the aquaculture requirements. Therefore, it is urgent to speed up the genetic and breeding research of the marble goby, and cultivate new variety with the ability to adapt to artificial compound feeds, fast growth, cold resistance, and disease resistance. This review summarizes the research progress of the marble goby around the world in the past half century. Firstly, we reviewed the feature and research progress of the reproduction, development and growth of embryos, larvae and adult fish of marble goby, and discussed the effects of temperature, salinity and hypoxia on marble goby. Secondly, we reviewed the achievement and progress of marble goby aquaculture, and the difficulties to overcome in the near future. Finally, we proposed the future directions for the marble goby research in aquaculture.

Abstract:In recent decades, genome resequencing has been widely applied to study the genetic diversity in wild populations or cultured populations, such as estimation of divergence of populations and detection of artificial or environmental selection on the chromosomes. However, owing to lack of bioinformatics skills, most of the researchers have to resort to commercial platforms to analyze resequencing data, which needs high costs and long analysis period. The commercial platforms usually use the universal pipelines without personalized analysis, which sometime causes the erroneous results due to unreasonable parameters or reference genome data. Owing to the increasing demands of genome resequence data analysis in aquatic animals, we developed a user-friendly software package to facilitate population genetics analysis of genome resequencing data for aquatic biologists who may lack bioinformatics skills. By surveying the current research and achievements in the analysis of resequencing data in aquatic animals, the constructed software package integrated different bioinformatic tools, encompassing mapping the quality-controlled reads to the reference genome, detecting genetic variations, performing phylogeny and principal component analysis, clarifying population structure, calculating quantitative indicators of genetic diversity, and completing selective sweep analysis. All of the resulting data were finally visualized with an R or a Python language package. The present package was tested by analyzing the resequencing data of 30 Larimichthys crocea individuals of 3 populations, which successfully completed all of the designed tasks, such as alignment of the reads, identification of single nucleotide polymorphism (SNP), construction of phylogenetic tree and population structure, illustration of linkage disequilibrium decay and calculation of main diversity indexes. The generated outputs were well-visualized. The software package functionally integrated most of the basic statistics, calculation, and plotting for the analysis of wild and natural populations, which enabled most of the researchers to locally perform the data mining of genome resequence data to save time and costs. The corresponding source codes and instruction manuals have been uploaded to GitHub: https://github.com/xqteng/Re-seq_analysis.

Abstract:The Indian Ocean is an important marine fishery production area, and its marine catch has shown a continuously increasing trend in the past several decades. The scientific prediction of the catch trend in the future is of great significance to the development of China's pelagic fishery. Based on the catch data of Indian Ocean from 2000 to 2016, the main catch categories affecting the total catch were analyzed by using the grey system theory and method, and the catch of 2017 to 2018 were used for GM (1, N) models verification. Based on the optimal GM (1, N) , the total catch in the Indian Ocean from 2019 to 2025 was predicted. According to the study, the main categories that affect the total catch in the Indian Ocean were bottom fish, crustacean, pelagic fish, other marine fish and cephalopod, and their grey correlation degree is above 0.70. The optimal prediction model is GM (1, 5) and GM (1, 6) , the average relative error is 1.83% and 1.90% respectively, and the grey correlation degree is above 0.9. The average relative errors for 2017 and 2018 are 3.78% and 3.42% respectively. The total catch projections for 2019–2020 and 2021–2025 in the Indian Ocean are 11.86-12.90 million tons and 12.27-13.24 million tons, respectively. The main increases in catches are likely to come from pelagic, cephalopod and bottom fish. The study concluded that the growth of the total catch in the Indian Ocean during the 14th five-year plan period would limited, with a total increase of less than 0.8 million tons, and that the total catch be basically at the stage of full development. It is recommended that the scale of fisheries development should be strictly controlled in the future in order to ensure the sustainable development of marine fisheries and the sustainable utilization of fishery resources in the Indian Ocean.

Abstract:Large yellow croaker (Larimichthys crocea) is an important marine fish species. The reduction of salinity can promote fish growth and reduce the risk of Cryptocaryon irritans infection. This study evaluated the effects of low-salt acclimation on oxidative damage and transcriptome in the liver of L. crocea under hypo-saline stress. Fish with an average weight of (52.46±1.47) g were pre-exposed to salinity 25 or 20 for 7 d, and subsequently were subjected to salinity 10 for another 24 h. The results indicated that hypo-saline stress increased reactive oxygen species (ROS) and lipid peroxidation (LPO), low-salt acclimation had no effect on ROS and LPO. Interestingly, low-salt acclimation with hypo-saline stress reduced ROS and LPO when compared with hypo-saline stress, suggesting low-salt acclimation alleviated hypo-saline stress induced oxidative damage. A total of 356, 478 and 484 differentially expressed genes (DEGs) were obtained from low-salt acclimation group vs. control, hypo-saline stress group vs. control, low-salt acclimation with hypo-saline stress group vs. hypo-saline stress group., respectively. The results of GO functional enrichment and KEGG pathway enrichment showed that DEGs were significantly enriched in GnRH signaling pathway, PPAR signaling pathway, apoptosis, MAPK signaling pathway and Toll-like receptor signaling pathway, indicating low-salt acclimation improved hypo-saline stress tolerance of large yellow croaker by regulating ion and material transport, lipid metabolism, apoptosis and nonspecific immunity. Those findings revealed the regulation mechanism of low-salt acclimation enhanced hypo-saline stress adaptation, and also provided scientific basis for factory farming and inland farming of L. crocea in fresh or brackish water.

Abstract:This study was conducted to investigate the effects of myo-inositol by different preparation methods on growth performance, plasma biochemical indicators, hepatic antioxidant capability and intestinal anti-inflammatory gene expressions of Cyprinus carpio var. jian. A basic diet (C, 34.64% of crude protein and 7.86% of crude fat) was formulated, and two experimental diets 400 mg/kg enzymatic myo-inositol (C+400E-MI) and chemical myo-inositol (C+400C-MI) in the basic diet were prepared. 180 healthy juvenile C. carpio var. jian [(1.50±0.01) g] were randomly distributed to 9 tanks in triplicate at the density of 20 fish per tank. After the 10-week feeding trial, the growth performance, liver antioxidant ability and intestinal inflammatory response-related gene expressions were determined. The results showed that the dietary E-MI and C-MI increased protein efficiency and protein deposition rate (P<0.05), and 400 mg/kg of dietary E-MI improved the weight gain rate and specific growth rate compared to the control group (P<0.05), and reduced the content of plasma lactate dehydrogenase (P<0.05). Compared to the basic group, 400 mg/kg E-MI supplementation significantly increased the activities of hepatic total superoxide dismutase (T-SOD), glutathione (GSH) and glutathione peroxidase (GPX) (P<0.05). 400 mg/kg C-MI supplementation significantly increased the hepatic GPX (P<0.05), while the content of malondialdehyde (MDA) increased as well (P<0.05). The intestinal gene expressions showed that the inclusion of E-MI and C-MI significantly down-regulated the mRNA expressions of pro-inflammatory factors in the fish intestine, e.g. IL-6, TNF-α and IL-12 (P<0.05). The inclusion of 400 mg/kg E-MI significantly reduced the mRNA expressions of anti-inflammatory factors, e.g. TGF-β1 and il-10 (P<0.05). In general, the supplementation of 400 mg/kg myo-inositol by different preparation methods improved the growth and feed utilization of juvenile C. carpio var. jian, and inhibited inflammatory response in the intestine. In addition, the enzymatic myo-inositol exhibited a better effect on growth improvement and antioxidant capacity enhancement of juvenile C. carpio var. jian. Therefore, enzymatic myo-inositol is a nutritional additive for aquatic animals that meets the requirements of green development.

Abstract:Litopenaeus vannamei is a major cultured shrimp, accounting for 70% of the total output of mariculture shrimp in China. Genetic improvement is an essential measure for improving the important economic traits in shrimp aquaculture. Understanding the genetic diversity and population structure of different populations using molecular markers is considered as a prerequisite for efficient germplasm exploitation and utilization to deploy suitable breeding program for genetic improvement. Using the criteria of motif repeats, a total of 10 453 975 potential SSRs with a minimum of five repetitions were identified from the 1 663 588 777 bp genome sequence by Perl script of MISA, which accounts for 18.56% of the total length of the genome sequence with a distribution density of 6 589.25 loci/Mb. A total of 42 SSR primer pairs were randomly selected for validation, and 14 SSR loci had allelic polymorphism. The genetic characteristics of three representative domestic populations including Guihai No.1 (CG), Haixingnong No.2 (CH) and Shandong population, and three foreign populations including Ecuador No. 1 (FO), Ecuador No. 2 (FT) and Mexico (FM) were evaluated using 14 polymorphic microsatellite markers. The results showed that 208 alleles were detected in six populations, the average allele number, average expected heterozygosity, average observed heterozygosity and polymorphism information content were 14.9, 0.462, 0.736 and 0.7411, respectively. The genetic diversity of six populations ranged from high to low: CH > FO > FM > CT > FT > CG. There was medium genetic differentiation between the Guihai No.1 and three foreign populations. The analysis showed that Guihai No.1 and Haixingnong No.2 clustered into one branch, while Shandong population and three foreign populations including Ecuador No. 1, Ecuador No. 2 and Mexico clustered into another branch. In conclusion, the 14 polymorphic markers could be used as efficient markers to analyze the genetic diversity of L. vannamei population, and the furthest distance was found between Guihai No. 1 and three foreign populations. This study analyzed the genetic background of six important populations of L. vannamei, which is of great significance to its development of breeding program.

Abstract:Environmental microbiota plays important roles in the intestinal microbiota of aquatic animals. Procambarus clarkii has become the most important commercial species of shrimp in China with high commercial value, and the main culture mode of P. clarkii is rice-crayfish co-existing. P. clarkii culture is an important economic mainstay in Hubei province, China. However, information on the gut microbiota of P. clarkii is limited. To study the difference of bacterial community structure in the intestinal tract of P. clarkii and the environment of rice- crayfish comprehensive culture system in different areas, and to provide some basis for improving the comprehensive culture strategy of rice in different areas, Illumina MiSeq high-throughput sequencing method was used to sequence and analyze the two high-variation regions (V3-V4) of 16S rRNA gene of microbia of the water, sediment and intestine of P. clarkii in different regions (Wuhan, Yongzhou and Shaoguan). Redundancy analysis (RDA)was used to analyze the relationship among water, intestinal microorganisms and environmental factors. The results showed that the diversity of the bacterial community in the water, sediment and crawfish gut of rice shrimp integrated culture system in Wuhan area was higher than those in Yongzhou area and Shaoguan area. The bacterial community structure in the water and sediment of the rice shrimp integrated breeding system in Wuhan area was similar to those in Yongzhou area and Shaoguan area. Actinobacteria, Cyanobacteria, Proteobacteria and Bacteroidetes were the dominant phylum in water, Proteobacteria was the dominant phylum in sediments. The dominant bacteria in the intestin of P. clarkii in Wuhan area were Proteobacteria, Firmicutes and Bacteroidetes at the phylum level, and Citrobacter (10.85%), Aeromonas (9.88%) and [Anaerorhabdus]_furcosa_group (8.43%) at the genus level. The dominant bacteria in the intestin of P. clarkii in Yongzhou area were Firmicutes and Actinomycetes at the phylum level, and ZOR0006(9.78%), Bacteroides (5.41%) and [Anaerorhabdus]_furcosa_group (3.98%) at the genus level. The dominant bacteria in the intestine of P. clarkii in Shaoguan area were Firmicutes and Proteobacteria at the phylum level, and Citrobacter (9.31%) , bacteroidetes (4.29%) and [Anaerorhabdus]_furcosa_group (4.58%) at the genus level. The results of correlation analysis between environmental factors and bacterial communities showed that TSS and TP had significant effect on the bacterial community structure of water, and PO₄^3--P and CODcr had significant effect on the intestinal microbial community structure. The results show that there are some differences among the gut of P. clarkii, water and sediment of different regions, and the microbial structure of water bodies and sediment is more similar. The microbial diversity in the water body of rice shrimp integrated culture system in Wuhan area is the highest, which is beneficial to the stability of the breeding system.The culture environment in different regions did not affect the core phyla of microorganisms in the culture system, but changed the relative abundance of dominant phyla and genera. The nutrient content of culture environment will affect the microbial community structure to a certain extent.

Abstract:Babylonia areolata is well-liked and has great market value, but its embryonic development success rate is very low and it is difficult to meet the market demand.. In this study, the effects of light intensity, light quality and photoperiod on fertilization rate ( FR ), hatching rate ( HR ) and metamorphosis rate ( MR ) during embryonic development of B. areolata were researched by factorial design. In addition, the result was analyzed by establishing regression models to optimize light conditions and find the best combination level of light quality, light intensity and photoperiod for embryonic development of B. areolata. The results showed that compared with other light conditions, green light had a better promoting effect on embryo incubation, and FR、HR and MR had maximum of 89.84%, 90.34% and 91.49%, respectively when photoperiod was 12L∶12D and the light intensity was 16 μmol/(m²·s). However, under the condition of blue light, FR, HR and MR were lower than other light qualities for any combination of light intensity and photoperiod levels, with maximum values of 49.71%, 50.26% and 43.49%, respectively. With the increase of light intensity and the extension of light time, the three indexes decreased more and more obviously, which indicated that blue light inhibited embryonic development of B. areolata. Through the establishment of model analysis found that under different light quality conditions, FR, HR and MR were significantly affected by the linear, interaction and quadratic effects of light intensity and photoperiod, that is, under any light quality condition, there was interaction effect between light intensity and photoperiod. The optimal light conditions were optimized when the light quality was used as a classification variable, it was found that under the condition of green light, the light intensity was 13.70 μmol/(m²·s), and the illumination time was 15.54 h, the FR, HR and MR reached the optimal value, which were 91.359 %, 88.637 % and 92.023 %, respectively. However, under blue light conditions, at a light intensity of 14 and a light duration of 6 h, the values of FR, HR and MR were 45.28 %, 47.69 % and 45.04 %. Compared with other light qualities, under the optimized conditions, the effect of green light on the embryonic development of B. areolata was the most obvious, followed by red, white light and blue light. In summary, appropriate light intensity and light duration can act synergistically with light quality, and in actual production, green light conditions can effectively improve the emergence efficiency and seedling quality of B. areolata, and blue light has an inhibitory effect on embryo development.

Abstract:In order to understand the nutritional requirements of Japanese eel (Anguilla japonica) larvae, the nutrients composition, amino acids and fatty acids were determined in the tissues of migratory glass eel from 6 different locations in the offshore of China. The results showed that the moisture content was 78.62%±2.03%, and the crude protein content, the crude fat content and the crude ash content were 69.08%±0.64%, 11.96%±1.33% and 11.45%±1.30%, respectively on a dry weight basis. No significant difference in moisture content from different sampling sites was observed. Samples from Zhoushan site had the highest crude protein content and the lowest crude fat content, which was significantly different from other sampling sites. Meanwhile, visible contents were found in the fish intestine from Zhoushan samples. In different migration locations, the amino acids with the highest content included glutamic acid, aspartic acid, lysine and leucine; while cysteine was the lowest. However, the only significant difference of amino acids content was found in samples from Zhoushan site. The C16:0, C18:1n9, C20:5n3 (EPA), C22:5n3, C22:6n3 (DHA) were the main components in samples from different sampling sites. The EPA and DHA accounted for 31.59%±1.00% of the total fatty acids, and the essential fatty acids contents were significantly different among samples from various sampling sites. Studies have shown that the theoretical requirements of essential amino acids and fatty acids were higher in the feed of larvae fish, which implied that both were important for the growth of glass eel. By comparing the nutrient composition of different sites and the theoretical feed requirements, it suggested that the marine environment at Zhoushan site contained more suitable food for glass eel, and further research is still needed to study the open bait for eel.

Abstract:Faba bean water extract could improve the muscle textural quality of grass carp (Ctenopharyngodon idella), but would cause oxidative stress, intestinal damage and decrease growth performance. In order to study whether there is a synergistic effect between vitamin C/vitamin E and faba bean water extract to jointly promote the change of C. idella muscle quality, reducing oxidative stress and improving growth performance, this study took ordinary compound feed as a control, 30% of faba bean water extract group, 30% of faba bean water extract + 400 mg/kg of vitamin C+ 200 mg/kg of vitamin E group and faba bean group were the experimental groups, fed (250±20) g C. idella for 120 days. The weight gain rate, condition factor, visceral somatic index, hepatopancreas somatic index, abdominal fat index, feed conversion ratio and survival rate, muscle and intestinal microstructure of C. idella at 120 days were detected. The content of reactive oxygen species (hydrogen peroxide, superoxide anion, hydroxyl radical, oxygen radical, total reactive oxygen species) in the muscles and intestines of C. idella, the activities of enzymes related to the generation and elimination of reactive oxygen species (SOD, CAT, GSH, G6PD, NADPH, COX Ⅰ, COX Ⅲ, COX Ⅳ), the changes of mitochondrial membrane permeability transition pore and the level of mitochondrial membrane potential in muscle cells were detected at 40, 80 and 120 d. The results showed that the growth performance of C. idella in the faba bean water extract group (FBW) and faba bean water extract+V_C/V_E group (FBW+V_C/V_E) was significantly improved compared with the faba bean group, and the muscle texture was significantly improved compared with the control group (P<0.05). The activity of enzymes related to reactive oxygen species (ROS) generation was significantly decreased, and the activities of enzymes related to ROS elimination increased in the faba bean water extract group and the faba bean water extract+V_C/V_E group. In addition, the faba bean water extract+V_C/V_E group showed better antioxidant capacity. Through the observation of microstructure, the muscle fiber density of C. idella in faba bean water extract group and faba bean water extract+V_C/V_E group was significantly increased, the diameter was significantly decreased, and the degree of intestinal injury was significantly lower than that in faba bean group. The present study demonstrated that V_C/V_E play an important role with being added into faba bean water extract in improving texture quality and growth performance of C. idella, and they would have a high potential for quality improving of aquatic products.

Abstract:Feed conversion ratio (FCR, %) is an important economic trait of turbot (Scophthalmus maximus). Improving feed conversion ratio through selective breeding can effectively reduce the breeding cost and improve the breeding profit, thus promoting the development of the industry. Microsatellite markers are commonly used in molecular marker-assisted breeding of fish. In order to screen out microsatellite markers related to feed conversion ratio of S. maximus and improve breeding efficiency, 300 juvenile S. maximus were used as experimental material in this study, and individual feed conversion ratio was measured through a special cage culture system. The 30 samples with the highest and lowest feed conversion ratios were selected as the high feed conversion ratio group (group H) and the low feed conversion ratio group (group L). 40 pairs of microsatellite primers were used to amplify the DNA mixed pools of S. maximus from groups H and L by PCR. The genotypes of individual PCR products of the two groups were counted, and the loci with different allele fragments between the two pools were screened. Through further population verification and family verification, the correlation between microsatellite loci and feed conversion ratio of S. maximus was analyzed. The results showed that the allele of microsatellite locus YSKr148 at 238 bp was significantly positively correlated with the feed conversion ratio of S. maximus (P<0.01), and the correlation coefficient reached 0.359. The feed conversion ratio of the positive group was significantly higher than that of the negative group in family verification (P<0.01). In this study, for the first time, molecular markers significantly related to feed conversion ratio of S. maximus were screened, which provided a basis for studying the genetic basis and related molecular mechanism of this trait, and laid a foundation for molecular marker-assisted breeding of this trait.

Abstract:In recent years, the development of antibiotic substitutes with the functions of immune promotion and vegetative growth is the development trend of aquaculture industry. In order to study the effect of dietary tea polyphenols (TP) on the growth performance, feed utilization and antioxidant ability of Megalobrama amblycephala, in the experiment, 240 M. amblycephala with an initial weight of (3.5±1.0) g were selected and randomly divided into 4 groups of 3 replicates, each with 20 fish in each replicate. Four isonitrogen isoenergetic formulation diets supplemented with 0 mg/kg (control group), 100, 300 and 500 mg/kg tea polyphenols were prepared. After the 8-week feeding trial, the growth performance, muscle composition, blood biochemical indicators , liver antioxidant indicators and intestinal antioxidant indicators were measured. The results showed that the WGR of the fish fed 300 mg/kg TP were significantly higher than those of the control group, the PER was significantly higher than those with lower supplementary TP, and the FCR decreased significantly. 500 mg/kg TP supplementation significantly reduced the crude fat content of fish muscle. The TP supplementation significantly reduced plasma GLU content. The content of MDA in the liver and intestines of fish fed 300 mg/kg and 500 mg/kg TP supplementary diets were significantly lower than those in the control group . The content of reduced GSH in the liver and intestine tissues of fish fed 100 mg/kg and 300 mg/kg dietary TP were significantly higher than that in the control group. In addition, the hepatic T-AOC and GSH-Px activity of the 300 mg/kg TP supplementary group were also significantly higher than those in the control group. After the feeding trial, acute liver injury was induced by intraperitoneal injection of 50% concentration of CCl₄ solution. It was found that at 24 hours post-injection, the fish survival rates of the 300 mg/kg and 500 mg/kg TP supplementary groups were significantly higher than those of the 100 mg/kg TP supplementary group, and the survival rates in 100 mg/kg TP supplementary group was significantly higher than the control group. Further analysis on the hepatic antioxidant indexes of fish at 24 hours post-injection, we found that the hepatic MDA content was significantly reduced in the TP supplementary groups. The activity of SOD of the 500 mg/kg TP supplementary group was significantly higher than that in the control group , the content of GSH of the 300 mg/kg TP supplementary group were significantly higher than that in the control group. Considering the physiological effects and practical applications, the dietary supplementation of 300 mg/kg tea polyphenols effectively promoted the growth and feed utilization and improved the antioxidant capacities, and the supplementation at 500 mg/kg impoved anti-injury capacities and protect against oxidative stress damage of M. amblycephala juveniles. The results of this study provide a basis for the study of tea polyphenols in the feeds of pomfrets and provide a reliable reference for their better application in breeding production.

Abstract:The clam Meretrix petechialis is an important commercial bivalve mollusk widely distributed in China, Japan and Korea. The development of clam culture depends on the plenty of seed supply. However, mass mortalities of M. petechialis larvae often occur during hatchery rearing. Outbreak of disease is the main bottleneck for successful spat production. So, the characterization of pathogenic bacterial strains causing epizootics in larval culture is essential for developing efficient management strategies to prevent and control disease outbreaks in clam hatchery. In present study, the moribund umbo larvae of clam sampled from hatchery were analyzed by constructing bacterial 16S rDNA clone library. The results showed that the bacterial community diversity of moribund larvae was low, and the Vibrio mediterranei clones accounted for more than 75% in the library, indicating they may be the causative bacteria of clam larvae mortality. Furthermore, the dominant strain was isolated from the moribund larvae, and identified as V. mediterranei by 16S rDNA sequencing and phylogenetic analysis. The virulence of the obtained strain US2-01 was determined by artificial infection test, a dose effect was observed for the pathogenicity of US2-01 on clam larvae. The onset time of US2-01 infection was related to its concentration, and the onset time was delayed in the low concentration group (1.0×10⁴ CFU/mL). The cumulative mortality rate of infected clam larvae was 84% when they were immersed in final concentration 1.0×10⁶ CFU/mL US2-01 for 96 hours. The clinical signs were observed during the artificial infection experiment, the treated larvae gradually lost their swim ability, showing symptoms such as the shedding of veliger cilia, partial tissue dissociation, and the empty stomach, which were consistent with the symptoms of the naturally diseased larvae in hatchery. Finally, the drug sensitivity test was performed and the results showed that V. mediterranei strain US2-01 was resistant to commonly used antibiotics such as penicillin, ampicillin and erythromycin, moderately sensitive to tetracycline and doxycycline, and highly sensitive to the other seven antibiotics such as ceftazidime, gentamicin and kanamycin. Taken together, this is the first report that V. mediterranei is the potential pathogen of M. petechialis larvae in hatchery. The results could provide a scientific basis for the disease research and control for larvae breeding in the clam hatchery.

Abstract:Hypophthalmichthys molitrix is the main freshwater aquaculture fish in China, which belongs to low-value fish due to the less content of fish meat and large amounts of bones. Therefore, it was necessary to produce deep processing food, such as surimi products,to realize high-value utilization of H. molitrix. However, the gelatinization of H. molitrix surimi was weak, which was not conducive to the formation of dense surimi gels. Currently, exogenous additives and physicochemical technology were usually used to improve the surimi gel properties. Ultrasonic technology is a new non-thermal physical technology to detect food quality and improve food characteristics. In addition, it is simple to operate and has many potential applications in food industry. Commonly, low-frequency and high-intensity ultrasound (16-100 kHz) was used in the modification of plant protein and animal protein which contributed to the cavitation effect.. More research focused on the mechanism of protein modification by ultrasonic technology, but few on its practical application. In order to improve the gel properties of H. molitrix surimi and realize the practical application of ultrasonic technology, this research explored the physical characteristics of surimi gel and the secondary structure of surimi protein by 0-50 min ultrasonic treatment, as well as the relationship between gel properties and secondary structure. Furthermore, the principle of improvement and deterioration of gel network by ultrasonic technology was explained. Thus, the effects of ultrasonic time on the gel strength, color, relaxation time and microstructure of surimi gels by low-frequency and high intensity ultrasonic technology were studied. Moreover, the changes of protein molecular weight and secondary structure in surimi after ultrasonic treatment were also investigated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared spectrometer (FTIR Spectrometer). The results showed that after ultrasonic pretreatment for 10 min, the gel strength of surimi increased significantly from (260.81±3.26) g·cm to (285.13±5.96) g·cm, and the tightness of surimi gel improved. And the gel matrix showed higher whiteness of 72.74±0.13, carried out by ultrasound in 10 min. Additionally, the proportion of immobile water was increased, and the capacity to bind water of gels was enhanced, which made the network structure more compact. However, with the increase of ultrasonic time, the gel strength decreased, and the immobile water was changing into free water. Therefore, the ratio of free water increased, and the internal structure of gels tended to be weak and loose. SDS-PAGE image proved that salt-soluble proteins (myosin, actin, tropomyosin) mainly consisted in surimi, and did not degrade or aggregate with the increase of ultrasonic time. While the relative content of α-helix decreased, β-sheet, random coil structure and β-turn increased after appropriate ultrasonic processing. Through Pearson correlation analysis, ultrasound pretreatment could promote the unfolding of salt soluble protein, which was more conducive to the formation of compact network structure, enhancing gel strength and water holding capacity in surimi processing. In conclusion, proper ultrasonic pretreatment could improve the gel properties of surimi by changing the three-dimensional structure of surimi protein, but excessive ultrasonic time was not beneficial to the formation of dense surimi gel. This research provided an experimental basis for improving the gel properties of surimi products, the practical application of ultrasonic technology and the innovative development of surimi products.

Abstract:Crab pots have become one of the main fishing gears for harvesting swimming crabs in the East China Sea since the 1980s. However, the tremendous fishing effort of the crab pot fishery in the East China Sea has brought great pressure on crab resources. Installation of escape vents on crab pots is one of the potential technical measures to improve the fishing efficiency of pots and conserve crab resources. In this study, to examine the effect of the location of escape vents on escaping behavior of Portunus trituberculatus in crab pots, the response behavior of P. trituberculatus to three rectangular escape vent configurations, including B32 vent, escape vent with 3.2 cm opening height and located at the bottom edge of the side panel, B40 vent, escape vent with 4.0 cm opening height and located at the bottom edge of the side panel, and T40 vent, escape vent with 4.0 cm opening height and located at the top edge of the side panel, was observed in a tank by infrared underwater cameras. Generalized linear mixed models (GLMM) with logit distribution were used to analyze the effect of the location of escape vents and quantitative behavioral indicators derived from underwater observations, including the number of crabs, duration of stay in pots, and so on, on the escaping behavior of crab. The results from underwater observation indicated that P. trituberculatus pre-stocked in the pots could detect and approach the bottom vents readily in their search behavior on the floor of pots. The detection and approaching of the top vents only took place in their vertical search behavior. Although the durations from ingress to first approaching and mean durations of all approaching the top vents ware more than those for bottom vents, no significant difference in the mean number of times of approach was detected between the top and bottom vents. For crabs approaching vents, 87% of them attempted to pass through the vents and there was no significant difference in the attempt to pass through between bottom and top vents. The model fit of GLMM indicated that no significant quantitative behavioral indicators affected the escape attempts of crabs. All crabs walked sideways through vents, so whether crabs pass through an escape vent depends upon carapace depth. To better match the top escape vents, crabs spent more time and effort adjusting their posture and location. However, the output of GLMM fit shows that the location of escape vents has no significant effect on the ratio of crab escape, which indicates that P. trituberculatus are good at manipulating their body, while the effect of the number of crabs inside pots was a significant factor. According to behavior observation, it is suggested that the efficiency of the escape vent could be affected by the activity of search behavior of crabs and soaking time. Taking into account the structure of the crab pot and the current status of fisheries, the authors recommended an escape vent mounted at the bottom edge of the side panel should be a feasible technical measure.