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Abstract:The differences in artificial reef structure is one of the main factors affecting the scale effect of the flow field. We selected six widely-used types of reef monocases, namely Da-zi, Mi-zi, Hui-zi, Frame, Cross, and Solid artificial reefs, to study the influence of reef body structure characteristics on the flow field effect in a uniform layout model and further establishe the scale effect model of structurally different unit reefs. The results showed that, based on the law of flow field effect, the indices of reef structure characteristics were volume ratio, permeability coefficient, and relative cross-sectional area of reef monocase. The volume effect model of upwelling was Vu=0.448Ru–1.679–Cp(29.868Cp–6.921)+ Rsa(56.18Rsa–35.42), and the back eddy volume model was Vb=Ru(1830Ru–128)–Rv(95Rv–105)+ Cp(138Cp–154)–Rsa(418Rsa–180). Finally, based on the volume effect model of the flow field, we propose suggestions for selecting structural parameters of the reef body, which provides reasonable parameter guidance for the structural design of an optimal reef based on the flow field volume.

Abstract:Illex angentinus is an important economic cephalopod worldwide, as well as an important fishing target for China’s mainland and Taiwan Province. Catch per unit effort (CPUE) is a widely used index to express stock abundance in fisheries. However, CPUE is susceptible to many factors; therefore, it must be standardized. In this research, the statistical data of squid fishing production and the corresponding environmental data from January to April, 2012 to 2017 in mainland China were selected, and the BP neural network method was adopted to establish a model to standardize CPUE. The model uses month, longitude (Lon), latitude (Lat), sea surface temperature (SST), potential temperature of the -95 m layer (PT95), chlorophyll-a (Chl-a), and sea surface salinity (SSS) as input factors. There were 12 hidden layers, from 4 to 15, and the output layer was CPUE. R2, mean squared error (MSE), and average relative variance (ARV) were used as the evaluation criteria of the model. The results showed that a 7-18-1 structure was the optimal model, and the input layer factors in order from high to low weights were SST, SSS, month, PT95, Lon, Lat, and Chl-a. The temporal and spatial distribution predictions for the same sea area indicated that although the BP neural network model could not accurately predict the specific values of CPUE, it could predict the temporal and spatial variations of CPUE, which could be used for the CPUE standardization of I. angentinus.

Abstract:Surfgrass Phyllospadix iwatensis belongs to the family Zosteraceae. Similar to most seagrass species, surfgrass beds has declined in the past decades. Unlike most of the seagrasses that colonize soft substrates (e.g., sand or mud), surfgrass grows predominantly on rocky substrates and can survive in high-energy environments. Therefore, the widely used transplanting methods for seagrasses growing in sandy or muddy sediments cannot be used in surfgrass transplantation. To explore the feasibility of restoring degraded surfgrass beds through transplantation, a transplanting unit was designed specifically for surfgrass, and a transplanting experiment was carried out from April 2019 to August 2020 at three sites with different hydrodynamic regimes (high, middle, and low levels) in the coastal area of Mashanli in Rongcheng, Shandong Province. After transplantation, transplant survival and morphological and physiological characteristics were examined bimonthly. The results showed that at 16 months after transplantation, the survival rates of the surfgrass transplants were 63.7%, 61.0%, and 60.0% under the high, middle, and low hydrodynamic regimes, respectively, but these differences were not significant. The plant size (shoot height, leaf width, rhizome diameter, etc.), photosynthetic pigment content (chlorophyll a, total chlorophyll and carotenoids), and soluble sugar and starch content were all highest under high hydrodynamic regimes, and significant temporal variations were observed in these measurements. The results suggest that a higher survival rate can be achieved in all the three hydrodynamic regimes by using the transplanting method, and the area of the high hydrodynamic regime is more suitable for the growth of surfgrass transplants. The results of this experiment confirmed the feasibility of restoring degraded surfgrass beds at any of the three hydrodynamic regimes in the Mashanli area using the transplanting system and methods applied in this study.

Abstract:With increasing concern over the negative environmental impact of mariculture, ecological aquaculture based on multi-trophic systems has received extensive attention in recent years. Phytoplankton are important components of aquaculture ecosystems. They are useful in maintaining water quality by uptake of nutrients during photosynthesis and serve as a direct or indirect food source for cultured organisms. Some phytoplankton, such as diatoms and green algae, are conducive to the growth of shrimp, crab, shellfish, and fish, whereas others (such as cyanophytes and dinoflagellates) may be toxic to aquatic organisms in aquaculture systems. In the present study, a combination of traditional morphological analysis and high-throughput sequencing was used to comprehensively assess phytoplankton community composition and diversity in the ecological aquaculture system of a marine pond in December 2018. Eight phyla were detected using two methods, Chlorophyta and Cryptophyta being the most frequently recorded. Notably, the phyla Haptophyta and Chrysophyta were only found via high-throughput sequencing. Additionally, a total of 39 genera were detected using two methods, but only five genera, Eutreptiella, Oscillatoria, Pseudonitzschia, Pyramimonas, and Teleaulax were shared in both methods. Some picophytoplankton (≤2 μm) and small nanophytoplankton (>2 μm and≤10 μm) were detected via high-throughput sequencing, but were not observed via morphological analysis. Picophytoplankton represented 25.24% of the total phytoplankton sequence abundance, and small nanophytoplankton accounted for 60.42%. Phytoplankton diversity revealed upon morphological analysis was lower than that revealed via high-throughput sequencing. Therefore, the combination of traditional morphological analysis and high-throughput sequencing will be useful for obtaining a comprehensive understanding of phytoplankton community composition and diversity in aquatic ecosystems. This study serves as a foundation for the characterization of phytoplankton community dynamics in the ecological aquaculture systems of marine ponds for future research.

Abstract:The increasing velocity method was adopted to test critical swimming speed of Gymnocypris przewalskii using a wild migratory group and cultured groups of the ages of 1 and 2 years old, and then the fixed velocity method was used to test the swimming endurance of G. przewalskii. Finally, we simulated a three-stage fish ladder and calculated and analyzed the efficiency of fish passing the ladder. The results showed that: The absolute critical swimming speed (Ucrit) of the wild migration group (35.73±6.56) cm/s was significantly lower than that of the 2-year-old cultured group (57.77± 10.25) cm/s (P<0.01), but there was no significant difference between the wild migration group and the 1-year-old cultured group (31.66±9.97) cm/s (P>0.05). The relative critical swimming speed (U′crit) of the 1-year-old cultured group (3.25±1.42) BL/s, the 2-year-old cultured group (2.71±0.61) BL/s and the wild migratory group (1.71±0.35) BL/s significantly decreased with the increase of body length and age (P<0.01). The U′crit of males in the wild migratory group (1.96±0.27) BL/s was significantly higher than that of the female (1.54±0.31) BL/s (P<0.01), while there were no significant difference between the sexes in the 1-year-old and 2-year-old cultured groups (P>0.05). The duration of swimming in wild G. przewalskii was very short at a high flow rate of 100 cm/s (27.67±5.67) s, and there was a significant negative correlation between the duration of swimming and the flow velocity (P<0.01). The passing rate of wild G. przewalskii at three levels of the fish ladder was significantly different (P<0.01), and the lowest pass rate was only 36%. This study shows that G. przewalskii, a typical cold-water fish in high altitude and high salinity environments, has a relatively weak swimming ability and is likely to be affected by dams and other obstacles during their migration. The results of this study could provide basic data for the design and optimization of fish ladders and the protection of the migratory populations of G. przewalskii.

Abstract:Fishways are important ecological compensation measures that come with the construction of waterpower dams. Investigation of their swimming capability will provide the basis required for the design of fishery passage facilities. In this study, we used four major Chinese carp species to measure critical swimming speeds under five temperature gradients (10℃, 15℃, 20℃, 25℃, and 30℃). The results showed that the relative critical swimming speeds of Mylopharyngodon piceus, Ctenopharyngodon idellus, Hypophthalmichthys molitrix, and Aristichthys nobilis were (3.93±0.24)~(9.94±1.65) BL/s, (3.50±0.48)~(10.55±2.07) BL/s, (0.95±0.04)~(4.68±0.58) BL/s, and (2.22±0.18)~(3.95±0.23) BL/s, respectively, across 10℃~30℃. The absolute critical swimming speed and relative critical swimming speed of the four major Chinese carp species increased with the increase in water temperature at 10℃ to 20℃. The absolute critical swimming speed and relative critical swimming speed reached a maximum at 20℃, and then tended to stabilize. The swimming capability at 20℃ was significantly higher than that at 15℃ and 10℃, but was not significantly different from that at 25℃ and 30℃. In addition, the critical swimming speeds of C. idellus increased faster than that of the other three species of the four major Chinese carp, as the temperature increased. At the same temperature, the critical swimming speeds of C. idellus and M. piceus were similar, and significantly higher than those of H. molitrix and A. nobilis (P<0.01). Based on the results of this study, we suggest that the opening time of the fishway should be extended in the summer in the year, and the critical swimming speed of A. nobilis should be taken as the main basis during fishway designing.

Abstract:Fish anatomy, including osteology and myology, is very important for traditional ichthyological research and systematics. It provides the basis for taxonomy, phylogeny, morphology, veterinary, evolution, and other studies. However, few related papers on fish anatomy have been published in China, and hence, research is currently insufficient. Liparis tanakae, is a dominant species in the Yellow Sea and Bo Hai, which occupies an important position in the ecosystem, but no study has so far described its anatomical characteristics in detail. The osteological and myological descriptions of L. tanakae are given in this study, and some associated nerves are also mentioned here. The osteological descriptions comprise ten parts: circumorbital bones, neurocranium, jaws, suspensorium and opercular bones, hyoid arch, branchial arches, pectoral girdle, pelvic girdle, axial skeleton, median fin supports, and caudal skeleton; and myological descriptions comprise eight parts: cheek muscles, cephalic muscles between the cranium and suspensorium-opercular bones, ventral muscles of the head, branchial muscles, pectoral fin muscles, pelvic fin muscles, muscles associated with median fins, and caudal fin muscles. Examinations were made on specimens stained with alcian blue and alizarin red. The specimens were dissected under a stereomicroscope used to prepare drawings. Some renewal conditions of terminology and synonyms were stated, and few portions unnamed in Chinese, such as hyohyoidei abductor and retractor dorsalis, were named. The special structure of the pelvic fin and its locomotory mechanism were illustrated, along with the differentiation and function of the cheek muscles.

Abstract:Turbot (Scophthalmus maximus) is an important mariculture species in northern China because of its high economic value. As a cold-water carnivorous fish, its rapid growth relies on high dietary protein in the form of fish meal. Fish meal is a major component of aquatic feed because of its highly digestible protein, balanced amino acids, and good palatability. However, global fish meal production is insufficient, and its price has soared due to overfishing and climate change. There is an urgent need to find high-quality protein sources to replace fish meal in the diet. Many experimental studies on replacing fish meal with protein sources have identified shortcomings. Plant protein sources contain anti-nutritional factors and defects in the amino acid profile, and have poor palatability; animal protein sources are unstable in their nutrient composition. Much work remains to be done to identify new protein sources. Insects are the largest organism community in ecosystems, and offer a new kind of protein source with great potential. The European Commission has recently approved the use of protein derived from insects in aquatic feed. Hermetia illucens is a saprophytic insect that can consume livestock manure and domestic waste to produce high-value animal feedstuff. Its larvae can be used as an alternative protein source to fish meal because they are rich in amino acids and polyunsaturated fatty acids. In addition, H. illucens is fed on decaying organic matter such as food waste, animal excrement, and animal and plant carcasses; the breeding cost is low, and the adults do not disturb humans. It can be added to the feed of sea bass (Dicentrarchus labrax), rainbow trout (Oncorhynchus mykiss), catfish (Pelteobagrus fulvidraco), large yellow croaker (Larimichthys crocea), grass carp (Ctenopharyngodon idellus), california bass (Micropterus salmoides), and Scophthalmus maximus (turbot). Most research has investigated the defatted dry powder of H. illucens. However, there are no reports on the replacement of fish meal with full-fat H. illucens in turbot. Therefore, in this study, we aimed to evaluate the application of H. illucens larvae as turbot feed. This experiment was conducted to investigate the effects of replacement of fish meal protein with full-fat H. illucens larvae meal on the growth performance, feed utilization, serum biochemical indexes, and skin color of turbot, in order to provide important information for turbot culture. Four treatments were designed for this study. Four isonitrogenous and isoenergetic diets were formulated with H. illucens larvae meal by substituting it into fish meal at 0% (FM), 20% (HI20), and 40% (HI40); the fourth experimental diet (HI40AA) was HI40 supplemented with methionine and lysine. A total of 1200 turbot [initial body weight: (26.57±0.54) g] were randomly distributed into four experimental diets, each group with three replicates, and each replicate with 100 juvenile turbot. The fish were fed twice daily to apparent satiation. The water temperature was kept at 11.0℃~14.4℃ and the water was changed twice daily. After the 56 d feeding trial, the results showed that H. illucens larvae meal significantly influenced weight gain and specific growth rate, which were significantly lower in the HI40 and HI40AA groups than in the HI20 and FM groups (P<0.05); no significant differences were observed in the feeding rate, feed conversion ratio, hepatosomatic index, viscerosomatic index, condition factor, or body composition, including crude protein and ash, among all groups (P>0.05). The serum cholesterol and high-density lipoprotein in the HI40 and HI40AA groups were significantly lower than those in the HI20 and FM groups (P<0.05), and the content of serum low-density lipoprotein in the FM group was significantly higher than that in the other groups (P<0.05). The values of L* (lightness) and a* (redness) of turbot dorsal skin color in the HI40 and HI40AA groups were significantly lower than those in the FM and HI20 groups (P<0.05). The value of b* (yellowness) of turbot dorsal skin color in the FM group was significantly lower than those in the other groups (P<0.05); it was higher in the HI40 group than in the HI20 and HI40AA groups (P<0.05). No significant differences were observed in skin color parameters in the ventral area of the turbot (P>0.05). In conclusion, the replacement of dietary fish meal with H. illucens did not affect the growth performance and physiological parameters of turbot when the replacement level was no more than 20%, which is therefore the recommended substitution level of fish meal by full-fat H. illucens larvae meal in the diet of juvenile turbot.

Abstract:To understand the distribution of perfect microsatellites in the genome of the channel catfish (Ictalurus punctatus), we used MISA, a bioinformatics software package, to search and analyze the microsatellites. A total of 510 256 perfect microsatellites were isolated from 29 chromosomes of I. punctatus, with a total length of 11 036 941 bp. The chromosome containing the largest number of microsatellites was chromosome 2 (25 284), followed by chromosomes 3, 1, and 5. Chromosome 29 had the lowest number of microsatellites (11 591). The length of each chromosome was significantly correlated with the number of microsatellites it contained (SPSS, r = 0.98, P < 0.01). The highest relative abundance of microsatellites was found on chromosome 27 (785.03 ind./Mb), and the lowest was on chromosome 11 (615.89 ind./Mb). Among the six repeat types, mononucleotides were the most frequent, accounting for 45.31% of the total, followed by dinucleotides (38.53%), trinucleotides (8.73%), tetranucleotides (6.93%), pentanucleotides (0.46%), and hexanucleotides (0.04%). The predominantly repeated microsatellite sequences in the I. punctatus genome were A, AC, AG, AT, AAT, AAAT, C, AAC, AAAC, and AAG, showing an obvious inclination towards A and T bases. The results of this study provide a reference for the further study of I. punctatus genome characteristics and contribute basic data for future investigations into molecular marker-assisted breeding and genetic information assessment of I. punctatus.

Abstract:To reveal the genetic mechanism underlying hypoxia adaptation, it is important to identify the molecular markers and candidate genes associated with hypoxia adaptation traits. Genome-wide association studies (GWSA) are frequently used in the genetic dissection of both quantitative traits and qualitative traits, while a large number of molecular markers and samples are needed. In this study, the GWSA of the hypoxia adaptation traits of common carp (Cyprinus carpio) was conducted. A total of 1243 samples were collected for the hypoxia stress experiment, and individuals with extreme traits in the hypoxia experiment were selected as the preliminary screening samples. The Carp 250 K single nucleotide polymorphism (SNP) array was used for genotyping, generating genotypes of 199 577 SNPs for 91 samples. After quality control with a genotyping call rate of over 95% and a sample call rate of 90%, a total of 87 222 SNPs and 90 samples were obtained for the association analysis. A principal component analysis (PCA) showed no population stratification in the samples from both the sensitive and tolerant groups. Taking the PCA results as a covariance, a logistic regression was used for the association test with a threshold of the false discovery rate value of 0.05. Four associated SNPs for hypoxia adaptation traits (carp229220, carp195901, carp001519, and carp063890) were identified, and 23 genes were found in the neighboring regions of the four SNPs, including TNF receptor-associated factor 4 (traf4), fatty aldehyde dehydrogenase (aldh3a2), peroxiredoxin 5 (prdx5), estrogen-related receptor gamma (esrrg), guanine nucleotide-binding protein subunit gamma-3 (eng3), G-protein coupled receptor 12 (gpr12), general transcription factor 3C polypeptide 4 (gtf3c4), transcription factor SOX-30 (sox30), and transcription elongation (tcerg1l). Additionally, seven SNPs passed the suggestive line, which could be validated in future research with larger samples. Putative genomic regions related to hypoxia adaptation for domesticated common carp were obtained in this study, which shed new light on the fine mapping and identification of causative genes and the underlying mechanisms of hypoxia adaptation.

Abstract:Microphthalmia-associated transcription factor (MITF) is a transcription factor with a typical basic helix-loop-helix-leucine zipper structure. It is a key transcription factor in the melanin synthesis pathway in animals by activating downstream genes to initiate melanin synthesis. In order to explore the regulatory action of mitf during body color variation in Amphilophus citrinellus, the full-length cDNA of the mitf gene was cloned using the rapid amplification of cDNA ends technique, and the difference in gene expression in different developmental stages of embryos, different stages of body melatonin, and various tissues in A. citrinellus were analyzed through qRT-PCR. Two mutant sequences of mitf were obtained. The full-length of mitf1 cDNA was 1816 bp, including a 158 bp 5′UTR, a 428 bp 3′UTR, and a 1230 bp ORF coding a polypeptide of 409 amino acids. The full-length of mitf2 cDNA was 1638 bp, including a 160 bp 5′ UTR, a 428 bp 3′UTR, and a 1050 bp ORF coding a polypeptide of 349 amino acids. The analysis of the homology and phylogenetic tree results showed that mitf1 and mitf2 clustered into a small branch in the phylogenetic tree, which had the highest homology with Cichlidae fish and low homology with mammals. The results of the qRT-PCR showed that mitf1 and mitf2 were expressed to varying degrees in various tissues of adult fish, among which the expression in the eyes was the highest and was significantly higher than in other tissues (P<0.05), and the expression in muscle, brain, and kidney tissue was also higher. The mitf1 and mitf2 genes were expressed in all stages of embryonic development, and the expression level was highest in the cleavage stage, which was significantly higher than the other embryonic stages. With the body color transition from black to orange, the expression of mitf1 and mitf2 genes decreased gradually in the fish skin, scales, and tail fins. It showed that the expression of mitf was positively correlated with changes in body color from black to yellow in A. citrinellus, which may be related to the dynamic change in the differentiation and distribution ratio of pigment cells in the body color development stage of fish. Through understanding the molecular basis of fish body color development and variation, this study accumulates data for fish pigment cell development and the artificial improvement of fish body color.

Abstract:In this study, the full length cDNA sequence of Rachycentron canadum dnd (Rcdnd) was cloned using RACE technology for the first time. In total, the sequence comprises 1339 bp, including a 5′-UTR of 59 bp, a 3′-UTR of 173 bp, and an open reading frame of 1107 bp, encoding a protein of 368 amino acids. The deduced amino acid sequence contains a conserved RNA recognition motif and four conserved regions (CR1~4). Comparisons of the deduced amino acid sequence with those of other teleosts revealed the highest percentage identity (72.3%) with Seriola dumerili. Phylogenetic tree analysis also showed that the dnd of R. canadum was most closely related to the homologous proteins of S. dumerili. Reverse transcription polymerase chain reaction (RT-PCR) results indicated that Rcdnd was specifically expressed in the gonads, but not in other tissues. The results of real-time quantitative PCR (qRT-PCR) revealed that Rcdnd expression tended to gradually increase as the testis developed (Stages Ⅱ to Ⅴ). During the development of the ovary (Stage Ⅰ to Ⅲ), Rcdnd expression first increased substantially and then stabilized; the highest expression level was found at 150 days post hatching (dph) (Stage Ⅱ). Furthermore, the results of chemical in situ hybridization revealed that Rcdnd mRNA was mainly expressed in germ cells but barely detected in somatic cells. In the testis, Rcdnd mRNA signals were concentrated in the periphery of spermatogonia and primary spermatocytes; they were only weakly detected in secondary spermatocytes and barely detected in spermatids and spermatozoa. In the ovary, Rcdnd mRNA was highly expressed in oogonia, and the signals became weak in primary oocytes dispersed in the perinuclear cytoplasm. There were no significant differences in Rcdnd mRNA signals detected in oocytes in phases Ⅰ, Ⅱ, and Ⅲ. In conclusion, these findings suggest that the Rcdnd gene may play an important role in gonadal development and provide a theoretical reference for revealing the regulatory mechanism of germ cell differentiation during gametogenesis in R. canadum.

Abstract:To evaluate the quality characteristics of Acipenser baerii, Acipenser schrenckii, and their hybrids, their muscle, amino acid, and fatty acid compositions were compared. The results showed that the contents of crude ash, crude protein, and crude fat in hybrid muscle were higher than in A. baerii and A. schrenckii muscle, but not significantly (P>0.05). Sixteen amino acids, including seven essential amino acids, were detected in the muscle of A. baerii, A. schrenckii, and their hybrids. The total amount of amino acids, essential amino acids, flavor amino acids, and nonessential amino acids in hybrid muscle were higher than in that of the parents. There was no significant difference between the muscle values (WEAA/WTAA, WEAA/WNEAA, and WDAA/WTAA) for the hybrid sturgeon and those of its parents (P>0.05). According to the amino acid and chemistry score, the first limiting amino acid in all muscle samples was methionine plus cysteine, while the second limiting amino acid was valine. In addition, 18, 18, and 22 fatty acids were detected in the muscle of A. baerii, A. schrenckii, and their hybrids, respectively. The contents of saturated fatty acids, monounsaturated fatty acids, and polyunsaturated fatty acids in hybrid muscle were significantly higher than in that of the parents (P<0.05). Palmitic acid (C16:0) was the most abundant saturated fatty acid, oleic acid (C18:1n9c) was the most abundant monounsaturated fatty acid, and linoleic acid (C18:2n6c) was the most abundant polyunsaturated fatty acid in all muscle samples. Additionally, the crude protein, crude fat, amino acid, and fatty acid contents in the muscle of the hybrid were higher than in that of the parents. The hybrid also has higher edible and nutritional value than the parent species, and so has more obvious production advantages.

Abstract:The deterioration of the aquaculture environment and disease outbreaks occur often in high-density pond cultures of fish. Probiotics are the main and efficient method to regulate the microbiota of the fish intestinal tract and pond water environments, which will improve aquaculture conditions and reduce the incidence of diseases. To investigate the effects of probiotics on the composition and diversity of microbiota in the intestinal tract and pond culture environment of the Japanese flounder (Paralichthys olivaceus), samples from the Japanese flounder intestinal tract and environmental media (culture water, feed, and pond sediment) were collected. High-throughput sequencing of the 16S rDNA genes was performed to analyze the regulation of the microbiota of the intestinal tract and environmental samples by probiotics. Our results showed that the diversity of microbiota in the pond sediment and intestinal tract of Japanese flounder increased after the addition of probiotics, and was still in the pond sediment. Inversely, the diversity of the microbiota in the culture water declined, which was lower than that in the intestinal tract. Firmicutes, Proteobacteria, and Fusobacteria were dominant in the Japanese flounder intestinal tract, and the relative abundances of Firmicutes and Proteobacteria increased, whereas Fusobacteria decreased after the addition of probiotics. At the genus level, the relative abundances of Enterobacter and Bacillus increased, whereas Acinetobacter and Photobacterium first increased and then decreased in the intestinal tract. The relative abundance of genus represented by NS3a_marine_group firstly decreased and then increased in the Japanese flounder culture water. In the pond sediment, the change in the relative abundance of Bacillus was obvious, increasing from 3.78% to 33.64%. The relative abundances of Vibrio in the fish intestinal tract, culture water, and pond sediment decreased after the addition of probiotics. Some strains of Acinetobacter and Vibrio are important pathogens in aquaculture. The microbiota structure in the intestinal tract of Japanese flounder was similar to that in the pond sediment. Changes in the relative abundances of these main microbiota indicated that the addition of probiotics could optimize the microbiota structure of the Japanese flounder intestinal tract and environment. However, it is impossible that Lactobacillus, as the main microbiota of the probiotics, was able to colonize and persist in the fish intestinal tract, water, and pond sediment, which indicated that probiotics did not deliver bacteria but their probiotic function. Hence, the addition of probiotics could affect the microbiota structure of the Japanese flounder intestinal tract, water, and pond sediment.

Abstract:In this study, in order to explore the effects of acute ammonia stress on the antioxidant and ammonia-nitrogen metabolism systems of Panulirus ornatus, lobsters were exposed to different concentrations of ammonia (0.24±0.07, 1.04±0.08, 9.75±0.21, and 19.87±0.46 mg/L) for up to 48 h. The activity of antioxidant and ammonia-nitrogen metabolizing enzymes and related gene expression were assessed in the gills and hepatopancreas at 0, 6, 12, 24, and 48 h after ammonia stress. From 6 to 12 h, total antioxidant capacity (T-AOC) and superoxide dismutase (SOD) activity in the gills and hepatopancreas of P. ornatus under ammonia nitrogen stress increased to varying degrees, and was significantly higher than that of the control group (P<0.05). In the high-concentration group, T-AOC and SOD activity was inhibited for 48 h. The LPO content gradually increased with prolonged stress and was significantly higher than that of the control group (P<0.05) at 48 h. The activities of the ammonia metabolism enzymes glutamine synthetase (GS), glutamate dehydrogenase (GDH), glutamic-oxalacetic transaminase (GOT), and xanthine oxidoreductase (XOD) were all up-regulated to varying degrees under ammonia stress compared with those of the control group, indicating that they are jointly involved in the metabolic transport of NH4+. Additionally, from 12 to 24 h, the expression of GDH and GOT genes in the hepatopancreas was significantly higher than that of the control group (P<0.05); the same trend was identified in gill tissue. In brief, different concentrations of ammonia stress induce different levels of antioxidant enzyme activity. Panulirus ornatus mainly synthesizes glutamine under the combined action of hepatopancreas GS, GDH, and other metabolic enzymes to avoid excessive ammonia in the body.

Abstract:Marsupenaeus japonicus is an important cultured species of marine shrimp in China. Its characteristics include a varied diet, fast growth, and tolerating periods out of water, as well as being suitable for live shrimp marketing and long-distance transportation. The suitable growth temperature of M. japonicus is 23℃~32℃. The culture cycle of M. japonicus is seriously affected by low winter temperatures in northern China, which increases the costs of parent shrimp overwintering. Therefore, it is necessary to breed new varieties with low temperature tolerances. M. japonicus was exposed to water at 10℃, 16℃, and 22℃ for 72 h, with M. japonicus exposed to water at 28℃ used as the control group. The results showed that the total antioxidant capacity (T-AOC), superoxide dismutase (SOD) enzyme activity, and GSH content in the gill and hepatopancreas decreased first, then increased and then decreased, while the MDA content and caspase-3 enzyme activity increased over time. The relative expression of the SOD and Caspase-3 genes decreased first, then increased, then decreased, and continued to increase, which was similar to their corresponding changes in enzyme activity. In order to prove that low temperature stress caused damage to the body of M. japonicus, a TUNEL test was performed. It was found that the apoptosis rate increased significantly with the extension of the stress time. The apoptotic rates of the gill control group, 3 h at 10℃, and 72 h at 10℃ were 2.03%, 6.20%, and 26.27%, respectively. The apoptotic rates of the hepatopancreas cells were 1.06%, 25.65%, and 42.33% for these exposure times, respectively. In conclusion, low temperature stress reduced the antioxidant capacity of M. japonicus, destroyed the original balance of the internal environment, and then led to oxidative damage. In this study, the changes in cell apoptosis and the antioxidant status of M. japonicus under low temperature conditions provided data that support the need to cultivate new varieties with low temperature tolerances.

Abstract:With the breeding technology development and progression of the breeding industry for Litopenaeus vannamei, their breeding has increased across the world, and high-density factory farming has become a new breeding mode for L. vannamei. However, with the scale and density expansion of breeding, there are a series of problems, such as germplasm degradation, water quality deterioration, and the emergence of frequent diseases. However, relevant research is insufficient at this stage in China, the layout of shrimp breeding is unreasonable, and planning is relatively poor, which severely restricts the survival and development of the L. vannamei breeding industry. Therefore, theoretical guidance on breeding capacity improvements is urgently needed. The establishment of a dynamic energy budget (DEB) model, an individual growth model based on the DEB theory to study the relationship between biological and physiological mechanisms and the environment, for L. vannamei, and further establishment of its aquaculture capacity, is of considerable significance for guiding aquaculture management and evaluating aquaculture capacity. Kooijman first proposed the theory of DEB based on the κ principle in 1986, which was used to describe the absorption, storage, and utilization of energy by organisms at the individual level. This indicates that a portion of the assimilated energy is used by organisms to maintain the growth of their own body, and the portion is used for development and reproduction. The DEB model can predict the dynamic growth of specific species´ body length, weight, and gonads at the individual level. Assuming that food and temperature are the main driving forces of biological metabolism, it provides a comprehensive framework for understanding the overall physiological performance of organisms. Therefore, to better control the individual dynamic growth status of the industrialized high-density culture of L. vannamei, this research utilized the DEB theory. With regard to the shrimp DEB model research method, five necessary parameters for constructing the DEB model of L. vannamei were obtained. The body length and wet weight of L. vannamei were obtained through biological measurements, and the shape coefficient (δm) was obtained by transforming and regressing the two values. According to the oxygen consumption rate per dry weight of L. vannamei under different experimental temperature conditions, the Arrhenius temperature (TA ) was calculated. According to the dry weight value of L. vannamei and the respiratory oxygen consumption rate in a starvation experiment, the values of three parameters (volume-specific costs for structure [EG], maximum storage density [EM] and volume-specific maintenance costs per unit of time [pM]) were calculated using the measured energy. The experimental results showed that the body length and volume of L. vannamei exhibited a cubic function relationship as per the statistical analysis: V=0.009 3L3.109 4 (R²=0.998 7), and the linear regression slope of the wet weight cube root and body length of the shrimp is the shape coefficient δm (δm=0.23). Three different experimental groups revealed a positive relationship of the oxygen consumption of L. vannamei per unit dry weight within the experimental temperature range of 22℃~34℃, with an inverse relationship after the temperature exceeded 34℃. Before the inflection point of 34℃, the ln value of the oxygen consumption rate per unit dry weight had a linear relationship with the reciprocal of the temperature T (thermodynamic temperature, K). The average value of the absolute slope values of the three regression equation sets was the Arrhenius temperature (TA) value (TA=6156 K). After the starvation experiment, the dry weight of L. vannamei decreased from the (2.36±0.32) g to (1.23±0.24) g, and the organic matter content decreased from 82% to 62%. The formula calculated the values of [EG] and [EM] were 5826 and 2211 J/cm3 respectively; the respiratory oxygen consumption rate stabilized from the initial 0.95 mg/(ind.∙h) to 0.58 mg/(ind.∙h), The value of [pM] (volume-specific maintenance costs per unit of time) is 31.47 J/(cm3∙d), calculated by the formula. To improve the accuracy and effectiveness of the study parameters, samples were collected over the entire growth process, and the values obtained were consistent with those of previous studies, within a reasonable range. Although the accuracy of the five model parameters obtained in this study needs to be improved, they are all effective. The L. vannamei DEB model constructed under optimal food and water temperature conditions is successful, and it simulates the feedback of the growth of L. vannamei to the environment in a detailed manner. The DEB model has been widely used for a variety of marine organisms worldwide; however, there is minimal research on crustaceans, such as shrimp. In this study, five necessary parameters for constructing the DEB model of L. vannamei were obtained through related experiments, which laid the foundation for the subsequent construction of the L. vannamei DEB model, and provided a reference for research on other crustaceans. The theoretical basis can provide support for the industrialized high-density farming of L. vannamei.

Abstract:Litopenaeus vannamei culturing industry is an important part of the rural economy in coastal areas. With the development of the shrimp farming industry, diseases breakout frequently. Antibiotic overuse can lead to bacterial antibiotic resistance and antibiotic resistance genes (ARGs). These then threatens human health and safety. Therefore, the evaluation of bacterial antibiotic resistance phenotypes and antibiotic ARG abundance can help to understand antibiotic pollution in specific areas. According to our preliminary investigation, more probiotics were used during L. vannamei culturing in Jiangsu Province. In order to avoid damaging the microbial community structure in ponds, less antibiotics were used during shrimp farming. To understand the relationship between bacterial resistance in L. vannamei intestinal culturable bacteria and different growth stages, four main culture models of L. vannamei in Jiangsu Province were selected as research objects. This study investigated the bacterial resistance to 12 antibiotics (tetracycline, doxycycline, fluorobenicol, chloramphenicol, sulfamethoxazole, cotrimoxazole, neomycin, gentamicin, ciprofloxacin, norfloxacin, ceftriaxone, and cefotaxime) and the abundance of nine ARGs (tetA, tetG, qnrA, qnrS, cmle3, floR, aadA, sul1, and sul2) of the intestinal culturable bacteria in samples using the K-B disc diffusion method and qRT-PCR technology. The results showed that Vibrio was the dominant bacterial genus among the shrimp intestinal culturable bacteria in different aquaculture models. The species and quantity of culturable bacteria in adult shrimp intestines increased significantly compared to those in post-larvae intestines (P<0.05). The proportion of antibiotic resistant bacteria decreased. The abundance of ARGs declined significantly (P<0.05). No obvious regularity was observed among the different aquaculture models. The antimicrobial resistance and abundance of ARGs in the intestinal bacteria of adult shrimp were lower than those in juvenile shrimp under different aquaculture patterns, indicating that reducing the use of antibiotics by administering probiotics may reduce the resistance of culturable bacteria in the intestinal tract of L. vannamei. In future research, the differences in the bacterial antibiotic resistance and ARG abundance in the intestinal tract of L. vannamei under different aquaculture models can be further explored by combining the methods of metagenomics.

Abstract:Estrogen-related receptor (ERR) is a eukaryotic transcription factor that is closely related to the effect of estrogen and is involved in the regulation of energy metabolism, cell proliferation and differentiation, gonadal development, and other physiological processes. To understand the role of estrogen-related receptors in the ovarian development of Exopalaemon carinicauda, the EcERR was cloned using RACE technology. The gene is 2025 bp long, including an open reading frame of 1374 bp, a 5′ untranslated region of 241 bp, and a 3′ untranslated region of 410 bp, which encodes 457 amino acids. Tissue expression analysis showed that EcERR was expressed in many E. carinicauda tissues, with the highest expression level in ovarian tissue. The expression level of EcERR in the cleavage stage was significantly higher than in that of other embryo and larval development stages (P<0.05). The expression level of EcERR first decreased and then increased during ovarian development, with the highest expression level in StageⅠ. After 5-hydroxytryptamine invaded, the expression levels of vitellogenin and EcERR in the experimental group were significantly higher than in the control group (P<0.05). The results showed that EcERR is involved in the regulation of E. carinicauda ovarian development and plays a key role in its early stages.

Abstract:The razor clam, Sinonovacula constricta, as a eurythermic bivalve, might have special adaptive mechanisms for defense against environmental stress because of its specialized lifestyle and limited mobility. To understand the expression characteristics of genes involved in different metabolic processes, quantitative reverse transcription PCR technology was used to analyze the expression levels of three types of temperature response candidate genes (molecular chaperone genes, metabolic and immune related genes, and apoptosis genes) based on a transcriptomic analysis in the gills and hepatopancreas of S. constricta under different acute high temperature conditions (30℃, 32℃ and 34℃). The results showed that the expression of molecular chaperone genes was significantly upregulated at 4 h under thermal stress and was positively correlated with temperature. Meanwhile, gills responded earlier than the hepatopancreas. The mRNA expression of metabolic and immune responses and apoptotic genes increased and then decreased in both tissues with the extension of stress time. In conclusion, the regulation of these genes played significant roles to maintain basic homeostasis in S. constricta under heat stress. The expression of immune response genes was more significant in the hepatopancreas. This study provides a theoretical basis for further exploring the molecular mechanisms of high temperature responses of S. constricta and provides candidate genes for molecular marker-assisted breeding in this species under thermal stress.

Abstract:Pyropia katadae var. hemiphylla is an important Pyropia species in China. Increasing consumer demand for P. katadae var. hemiphylla has led to its commercial breeding and floating raft cultivation in Jiangsu Province and Shandong Province in China in the past two years. However, it remains to be determined what the optimum iron concentrations for the growth of conchocelis and conchosporangial formation of P. katadae var. hemiphylla are and to understand the physiological and biochemical adaptability to different iron concentrations. Therefore, relative growth rate, ratio of conchosporangial formation, and physiological and biochemical indexes (including chlorophyll fluorescence parameters, contents of reactive oxygen species, contents of antioxidant, and activities of antioxidant enzymes) under different iron concentrations were studied. From the results of these experiments, the main conclusions are as follows: Growth, maximum photochemical efficiency of photosystem Ⅱ (Fv/Fm), and quantum yield of regulated non-photochemical energy loss in photosystem Ⅱ [Y(NPQ)] of P. katadae var. hemiphylla increased significantly at an iron concentration of 0.040 mg/L, suggesting that this iron concentration improved the photosynthetic efficiency and photoprotective efficiency of vegetative conchocelis. Relative growth rate (RGR) decreased significantly in groups with high iron concentrations (0.160~0.800 mg/L), while the ratio of conchosporangial formation increased significantly at high iron concentrations. These results indicate that high iron concentrations inhibited the vegetative growth of conchocelis, while promoting the transition from vegetative growth state to developmental state. There was a significant positive correlation between the ratio of conchosporangial formation and Fv/Fm, indicating that the photosynthetic efficiency of conchocelis was significantly improved after the transformation of vegetative conchocelis to conchosporangia filaments. The addition of iron resulted in significant accumulation of reactive oxygen species (ROS) in conchocelis. The contents of carotenoids and proline, and the activities of SOD, POD, and GR in P. katadae var. hemiphylla may have increased so that the ROS level was reduced under high iron stress, thus balancing ROS production and ROS clearance. These results can provide a theoretical basis for the application of iron nutrition in the cultivation of P. katadae var. hemiphylla.

Abstract:This study aimed to compare the edible yield and flavor characteristics of Chinese mitten crabs (Eriocheir sinensis) from four regions in Jiangsu Province, China, to provide a theoretical basis and guidance for understanding consumer preference. For this, representative authentic Chinese mitten crabs from Yangcheng Lake, Gucheng Lake, Tai Lake, and Xinghua were used. The edible yield, flavor profiles, free amino acids, flavor nucleotides, and free fatty acids were measured, and the degree of flavor was evaluated using the taste activity value and equivalent umami concentration (EUC). The results showed that Tai Lake crabs had the highest edible yield [(33.08±0.31)% in male crabs, (37.65±1.09)% in females]. Yangcheng Lake and Gucheng Lake crabs had similar flavor profiles, as did Tai Lake and Xinghua crabs; however, Yangcheng Lake and Gucheng Lake crabs were sweeter, whereas Tai Lake and Xinghua crabs had a better umami flavor, although their bitterness and astringency were also high. Yangcheng Lake crabs had the highest sweet amino acid content in whole edible parts, male crab meat, female crab meat, and crab yolk: (676.65±1.30) mg/100 g, (899.00±2.88) mg/100 g, (950.34±4.78) mg/100 g, and (309.86± 0.73) mg/100 g, respectively. Whole edible parts and male crab meat from Tai Lake crabs had the highest umami amino acid content [(98.06±4.07) mg/100 g and (123.76±6.72) mg/100 g, respectively] and the highest EUC values [(11.62±0.66) g MSG/100 g and (15.29±2.58) g MSG/100 g, respectively]. Finally, total free fatty acids in Yangcheng Lake, Gucheng Lake, and Tai Lake crabs were higher than those in Xinghua crabs. In conclusion, the results indicate differences in the edible yield and flavor of Chinese mitten crabs from different locations. Overall, Yangcheng Lake crabs had the most prominent sweet flavor. Tai Lake crabs had the highest edible yield and their flavor profiles included a marked degree of umami; however, they also had a bitter flavor. Umami flavor was present in female crab meat and crab yolk from Yangcheng Lake and Gucheng Lake, in addition to male crab meat and crab paste of Tai Lake and Xinghua.

Abstract:To make full use of shrimp head waste, the protein, amino acid, phospholipid, astaxanthin, and chitin contents were determined from the fresh heads of four shrimp species, and the quality of the different shrimp heads was compared and evaluated. These shrimp heads came from four common species in the Shandong Province: Procambarus clarkia, Penaeus japonicas, Penaeus orientalis, and Penaeus vanmamei. The results showed that the weight ratio of the head waste to the whole shrimp weight for the three penaeids reached approximately 40%. The highest weight ratio (85.52%) was observed for P. clarkia. All shrimp heads were rich in protein, ranging from 12.47%~14.91% of the fresh shrimp head weight. The essential amino acid contents in the shrimp head proteins of the four species reached more than 40%, and the umami and sweet amino acid contents were also high. Therefore, the shrimp heads of these four species are suitable for the development and utilization of protein hydrolysate/peptide amino acids. The phospholipid contents were 12.38~15.00 mg/g for the three penaeid species heads, and only 3.39 mg/g for the P. clarkia heads. The relatively higher astaxanthin content was 68.46 μg/g for P. vanmamei and 61.62 μg/g for P. japonicas, followed by 41.42 μg/g for P. orientalis and 30.71 μg/g for P. clarkia, respectively. Therefore, the penaeid heads can be used as a raw material for extracting phospholipids and astaxanthin. However, the chitin content in the head of P. clarkia was about 3-fold more that of the three penaeid species, reaching about 4.67%, making it suitable for the preparation of chitin-related products. Findings of this study show that the by-products of the shrimp heads of these four species are rich in protein and amino acids, while the phospholipid, astaxanthin, and chitin contents varied significantly in the shrimp heads. Therefore, high value-added bioactive components can be developed from the shrimp heads of different species and may have a wide range of application.