Abstract:The utilization of inorganic carbon in filaments of Scytosiphon lomentaria was investigated by pH-drift technique and pH electrode method combined with related inhibitors. The influence of different concentrations of carbon dioxide on the activity of intracellular carbonic anhydrase (CA) was also explored at the same time.The results showed that (1)the pH compensation point of filaments of S. lomentaria was 9.21 and the CO₂ compensation point was 0.74 μmol/L.Acetazolamide (AZ) has no significant influence on the pH compensation and the inorganic carbon uptake amount in the first three hours of the inhibitor experiment. Ethoxyzolamide (EZ) and vanadate (Van) decreased the pH compensation point to the same value 8.82 and the inorganic carbon uptake amount inhibition rates were 55.93% and 56.72%, respectively, in the first three hours of the inhibitor experiment. Under natural conditions, filaments of S. lomentaria use free CO₂ and HCO₃^- as inorganic carbon source, and the utilization of HCO₃^- depends on ATPase and intracellular CA. (2) 0.35%, 0.70% and 1.20% CO₂ can inhibit the activity of intracellular CA of filaments of S. lomentaria and the inhibition rates were 6.29%, 17.44% and 27.15%, respectively. The higher CO₂ concentration, the stronger inhibition effect of the activity of intracellular carbonic anhydrase.

Abstract:The relationships between muscle fat content and biological parameters of the yellowfin tuna (Thunnus albacares) were studied to determine if there were any relationships between them and to better understand its characteristics of growth, reproduction and the fishing ground. The biological data and muscle fat content of 91 yellowfin tuna were collected from the longline fishery in waters of 6°33'N~10°33'S, 44°54'E~68°32'E, Western Central Indian Ocean from October, 2013 to April, 2014. Histogram count figures were obtained to show the spatial or temporal distribution of fat content and fat content by gender, dressed weight, and gonad maturity. A generalized additive model (GAM) was used to analyze the relationships between fat content and condition factor (K), somatic index (SI), gonadosomatic index (GSI) and fork length (FL). Results showed that:① the fat content of yellowfin tuna was in the range of 0.1%–26.7%, and the average was 6.94%; ② the fat content of yellowfin tuna was low from October to December, 2013, and then was increasing after December, 2013. The fat content of (2°N~3°N, 59°E~60°E) was the highest (15.3%) and that of (7°S~8°S, 44°E~45°E) was the lowest (1.2%), and there was significant differences among them; ③ there was no significant difference among the fat contents by gender, gonad weight, gonad maturity stages or fork length; ④ By GAM, the results showed that there was no significant correlation between fat content and K, SI, GSI or FL. Results of this study suggest that:① the yellowfin tuna begin to reproduce in March and April; ② the area of 2°N~3°N, 59°E~60°E might be an important spawning ground; ③ there was no significant correlation between female reproductive capacity and muscle fat content.

Abstract:Sebastiscus marmoratus was the main economic fish in Gouqi Island offshore waters of north-east Zhoushan Islands, which played an important part in local fishery. This research used carbon and nitrogen stable isotope technology to analyze the feeding habit of S. marmoratus in different seasons and developmental stages and evaluated the nutrition contribution from food organism such as zooplankton, amphipoda, shrimp, crabs and small fishes. It showed that in the four seasons of Gouqi Island offshore waters, the δ¹³C value of S. marmoratus was between -18.2‰ and -14.7‰, of which the average value was -15.6‰; the δ¹⁵N value was between 3.3‰ and 9.9‰, of which the average value was 7.9‰. One-Way ANOVA showed that the δ¹³C value and that of δ¹⁵N were insignificantly different between seasons. This indicated only a slight difference in the feeding habit between different seasons. A linear-regression analysis was carried out, which analyzed the whole body length and the carbon and nitrogen stable isotope ratios and showed the δ¹³C and δ¹⁵N values changed with the body length significantly, which indicated the differences of the feeding habits of different developmental stages were very significant. Cluster analysis divided S. marmoratus with different body length into three groups:one group with the length of 0 to 19 mm, another group 20 to 79 mm and 80 to 109 mm and the third one 110 to 199 mm. ANOSIM analysis showed the differences between the three groups were quite significant. The δ¹³C value of S. marmoratus was close to that of the food organism such as shrimp, crabs and small fishes. When analyzing the nutrition contribution of food organism with IsoSource Software, the research found Caprellidae's average nutrition contribution to S. marmoratus was the greatest, i.e. 22.3%, and that of the fishes, shrimp and crabs was all above 12%. Based on the δ¹⁵N value of S. marmoratus of Gouqi Island offshore waters, the average trophic level was 3.18, indicating that the S. marmoratus was of low-level carnivores feeding on Caprellidae. The research found that S. marmoratus was benthos feeders rather than zooplankton feeders and Caprellidae, fish, shrimp and crabs etc. were the main food source.

Abstract:In this study, emergy analysis method was used to evaluate the benefits and driving forces of largemouth bass (M. salmoides) aquaculture system from ecological and economic points. For analysis, a number of different inputs have been identified and grouped in two categories:renewable environment resource inputs and purchased external resource inputs. The first group counted five natural, free and renewable inputs (solar radiation, wind, rain, earth cycle and river water), while the second group included eight external inputs (construction, fingerlings, electricity, feed, medicine, labor, rent and maintenance). Emergy indices for the largemouth bass aquaculture system calculated from the emergy evaluation, such as Transformity (TR), Emergy Yield Ratio (EYR), Environmental Loading Ratio (ELR), Emergy Exchange Ratio of Yield (EER_Y), Emergy Sustainability Index (ESI) and Emergy Index for Sustainable Development (EISD), were applied to characterize the resource utilization, environmental impact and the overall sustainability of the largemouth bass aquaculture system. These indices were compared with those of four other fish farming systems:the large yellow croaker (Larimichthys crocea) aquaculture system around Dongji Island in Zhoushan, China, the eel aquaculture systems on wetlands surrounding the Pearl River Estuary, China, the polyculture system of ophicephalus and mullet on wetlands surrounding the Pearl River Estuary, China and the dike-pond agro-ecological engineering system in Sanshui city of the Pearl River Delta. The results showed that the total emergy inputs was 4.51×10¹⁷ sej/(hm²·a). The renewable emergy inputs was 1.24×10¹⁶ sej/(hm²·a), which accounted for 2.75% of the total emergy inputs. The external emergy inputs was 4.38×10¹⁷ sej/(hm²·a), which accounted for 97.25% of the total emergy inputs. More than 70% of the emergy inputs into the largemouth bass aquaculture system was feed (77.33%). Labor was the second largest emergy input to the system (5.08%). The river water emergy was the major renewable environment resource input for largemouth bass aquaculture system (2.75%). The TR of this system was 2.18×10⁶ sej/J, EER_Y was 2.028, and EYR was 1.028. The ELR was 35.39, ESI was 0.029, and EISD was 0.059. The lower ESI with EISD and the higher ELR showed that the purchased external resource emergy inputs achieved a greater effect than renewable environmental resource emergy in largemouth bass aquaculture system, and the system had more dependence on purchased external resource emergy inputs, which indicated that the largemouth bass aquaculture system was less sustainable. The result showed that measures which reduced feed inputs and improved the feed utilization efficiency, such as using feed and additives with low feed coefficient, increasing feeding frequency, etc., could reduce the purchased external resources inputs, and then elevate the ESI and EISD of the largemouth bass aquaculture system. Integrated aquaculture was another method which could get the same result.

Abstract:In order to comprehend whether the polymorphism of grass carp GH gene was associated with growth traits and muscle compositions, 156 individuals from Yangtze River were used in this study. Nine polymorphic loci were found in the GH gene 3' partial sequence:G2825A、G2914T、T2966G、A3002T、T3022C、A3301G、C3463T、C3547T、C3620T, which were named SNP1-SNP9 respectively. Nine loci were not significantly deviated from Hardy-Weinberg equilibrium based on Chi-square test (P>0.05), and performed moderate polymorphism (0.25 <PIC< 0.5). The results of linkage disequilibrium showed that SNP3, SNP4, SNP5 were a set of completed linkage disequilibrium (r²=1) and SNP2, SNP7, SNP9 were a set of completed linkage disequilibrium (r²=1). Haplotype analysis for five loci in GH 3'partial sequence revealed 6 haplotypes, which Hap1(30.4%) had the greatest proportion, Hap6(4.8%) had the lowest proportion. A general linear model and multiple comparisons were used to analyze the correlation between those single nucleotide polymorphisms (SNPs) and grass carp traits. The results showed that the body weight, body length and fat content of individuals with the homozygous mutant genotype at SNP2 and SNP3 were significantly higher than wide-type and heterozygous mutant genotype. Similar results were found in diplotype combinations analysis. The body weight, body length and fat content of combination with heterozygous mutant genotype at SNP2 and SNP3 were significantly higher than other combinations. The results showed that the polymorphism of SNP2 and SNP3 in grass carp GH gene had a significant correlation with growth traits and muscle composition (P<0.05), and it might have utility as markers for practical breeding programs for growth traits and muscle composition in grass carp. Meanwhile, we have laid a foundation for further research on the functional verification of the relevant mutation sites.

Abstract:To study the effect of bivalve on meiofauna in shrimp ponds, physical and chemical characteristics of sediment, abundance and biomass of meiofauna were analyzed both in monoculture and polyculture of shrimp (Litopenaeus vannamei) with bivalve (Tegillarca granosa). Four treatments with different stocking density of bivalve[0 ind/m² (S), 60 ind/m² (SC1), 120 ind/m² (SC2), 180 ind/m² (SC3)] were designed, and each treatment was stocked with 17×10⁴ ind/hm² of shrimp. The results showed that, with the increase of culture time, ①organic matter content showed an upward trend. pH value and ORP were gradually decreased; increase of bivalve stocking density is beneficial to slowing the progression of the deterioration of sediment environment. ② The abundance and biomass of meiofauna showed a downward trend; community structure of meiofauna was more stable with the increase of bivalve stocking density. ③ Regression analysis showed that the ratio of ostracoda to nematodes had obviously positive correlation with the shrimp yield. A certain density of polyculture with bivalve was conducive to increasing the ratio of ostracoda to nematodes. A preliminary result showed that, to have a good yield, the average ratio was better to reach 6 during shrimp culture, and a single value was not less than 3.5. Therefore, shrimp polyculture with bivalve was conducive to sediment quality improvement and can increase growth of meiofauna, and higher density (80-140 ind/m²) of bivalve had a clear function of purification of the sediment.

Abstract:Ribosomal DNAs were mapped comparatively with fluorescence in situ hybridization (FISH) in Argyrosomus amoyensis and Larimichthys crocea to explore the variations of karyotype microstructure among Sciaenids. The results showed that the karyotypes were quite different between A. amoyensis and L. crocea referring to macrokaryotype, and distribution mode of 18S rDNAs and 5S rDNAs. In A. amoyensis, the karyotype is 2n=48t (FN=48); single pair of 18S rDNA signals were mapped at interstitial region of Chromosome 1; and single pair of 5S rDNA signals were located at proximal region of Chromosome 3. In L. crocea, the karyotype is 2n=2sm+4st+42t (FN=50); single pair of 18S rDNA signals were mapped at terminal region of short arm of Chromosome 18; and 9~11 pairs of 5S rDNA signals distributed mostly on centromeric termini of acrocentric chromosomes or terminal on the short arms. Together with the available cytogenetic data of Sciaenids, the following conclusions were drawn:(1) the karyotype of A. amoyensis represents characteristics of ancestral karyotype in Sciaenidae, while the karyoytpe of L. crocea was derived from the ancestral karyotype through rearrangement and transposition; (2) the macrokaryotype and the location of 18S rDNA sites were rather conservative in Sciaenidae with several exceptions, while the 5S rDNA sites varied dynamically among species. Hence, further studies to investigate microstructure variations of karyotypes among Sciaenid species with FISH should be encouraged.

Abstract:In order to provide reference for effective prevention and control of the bacterial septicemia of Palea steindachneri, the present experiment was conducted to investigate the pathogen of P. steindachneri with bacterial septicemia and the presence of six virulence genes. The pathogen was isolated from the heart and liver tissues of P. steindachneri by using conventional methods, and the pathogenicity of the strains was confirmed by artificial infection. Then the pathogen was identified based on API 20NE bacteria identification system and PCR amplification of 16S rRNA gene. Presence of virulence genes was determined using the polymerase chain reaction. Results showed that four dominant strains named SRB125, SRB142, SRB143 and SRB345 were isolated from the heart and liver tissues of diseased P. steindachneri. The mean fatality rate of healthy P. steindachneri was 97.50%–100.00% and the pathogenic bacteria of bacterial septicemia of P. steindachneri were the four isolated strains. According to the biochemical and molecular identification results, the four isolated strains were all Aeromonas hydrophila, and they had the closest genetic relationship with A. hydrophila L3-5 (KP716701), sharing homology of 99.9%. The four strains contained two virulence genotypes, hly⁺Aer⁺Alt⁺Act⁺ahal⁺ahp⁺ and hly⁺Aer⁺Alt⁺Act⁺ahal⁺ahp^-, each accounting for two strains. Strain SRB143 from Nanning City and SRB345 from Guiping City all lacked gene ahp.

Abstract:The Y-box protein family is highly conserved nucleic acid binding proteins which are conserved from bacteria to human. In this study, the cDNA encoding cold shock protein Y-box from oriental river pawn Macrobrachium nipponense (MnY-box) was cloned by using EST analysis and rapid amplification of cDNA ends (RACE) approach. The full length cDNA of MnY-box was 1501 bp, consisting of a 5' untranslated region of 84 bp, a 3' untranslated region of 541 bp, and an open reading frame of 876 bp. The deduced protein had 291 amino acid residues with molecular mass of 31.48 kDa. Based on the protein similarity comparison, the Y-box protein family was very conservative in CSD domain. Phylogenetic tree analysis stated that oriental river prawn has the closest relationship with Daphnia pulex. Quantitative real-time RT-PCR analysis showed that the MnY-box gene was expressed in haemocytes, hepatopancreas, muscles, gill, brain, testis, ovary and intestines with the highest level of expression in the hepatopancreas. After environmental low temperature and recovery challenge, the relative expression level of MnY-box in hepatopancreas was significantly higher compared to the control group at 3 h to 12 h post-low temperature, followed by return to control levels at recovery 12 h. What's more, we constructed prokaryotic expression system and obtained the recombinant proteins of M. nipponense Y-box, which may provide information for further functional study.

Abstract:The purpleback flying squid Sthenoteuthis oualaniensis is widely distributed in tropical and subtropical areas of the Pacific Ocean and the Indian Ocean. In the northwest Pacific, the highest concentration is found in the South China Sea, while the waters of Ryukyu Islands and southwest Taiwan are regarded as fishing grounds of S. oualaniensis. To manage this squid and exploit it scientifically, it is important to investigate the genetic structure of its population. In this study, the genetic diversity of S. oualaniensis from the northwest Pacific (including the South China Sea, the East China Sea, and the Philippine Sea) was revealed, and sequence analysis of the mitochondrial DNA cytochrome b gene (Cytb) was used to assess its genetic structure. A total of 105 partial sequences of cytb were obtained, each 896 bp long, from which 72 haplotypes were defined. Haplotype diversities and nucleotide diversities for all geographical populations were 0.982±0.006 and 0.012±0.006, respectively, with corresponding maximum values of 0.973±0.014 and 0.015±0.008, respectively, in the population from the Philippine Sea. Haplotype diversities in populations from the South China Sea and the East China Sea were 0.959±0.026 and 0.943±0.031, respectively, while nucleotide diversities were 0.006±0.003 for both areas. Three populations from the South China Sea, the East China Sea, and the Philippine Sea were characterized by a higher haplotype diversity and higher nucleotide diversity. Analysis of molecular variance showed that 34.6% of genetic variance came from individuals among populations, and highly significant genetic differentiation was detected; a similar result was obtained from the fixation indices (F_st) among the three populations. The neighbor-joining haplotype tree and reduced median network analysis detected three distinct lineages (A, B, and C), and highly significant genetic differentiation was detected among the lineages (F_st=0.735-0.805). Neutrality tests and mismatch distribution analysis suggested that lineage B recently experienced a population expansion, around 103 000-125 000 years ago. In summary, the genetic structure and phylogeographic pattern of S. oualaniensis in the northwest Pacific appear to have been caused by ocean currents and climatic changes since the Pleistocene. The northwest Pacific S. oualaniensis should be considered as at least three stocks in their assessment and management.

Abstract:By using histopathology and polymerase chain reaction (PCR) methods, studies were carried out to find the cause of the white-gill disease in Larimichthys crocea cultured in cage in Zhejiang Province. White-gill diseased fish had the typical symptom of pale gills and there is no ulcer in the body surface of infected fish. However, the blood and blood cell counts in the white-gill disease fish were significantly decreased. Pathological observation showed serious pathological changes in internal organs. In white-gill diseased fish, haemocytes, in particular, erythrocytes reduced sharply in the blood vessels of liver, spleen and other organs and degenerative changes occurred in red blood cells, too. Under electron microscope, a large number of viral particles were observed in the cytoplasm of spleen, with an average diameter of 40 to 45 nm. With the primers derived from RSIV, no fragments of the RSIV DNA could be amplified from the white-gill diseased fish. The results indicated that although white-gill disease and RSIVD both can lead to the symptom of pale gills, but the pathogen that caused each disease was completely different, and the white-gill disease that broke out in Zhejiang may be associated with another virus.

Abstract:In order to establish a rapid assay for inactivated infectious spleen and kidney necrosis virus (ISKNV), ISKNV ORF099 was selected as a promising target gene based on the results of transcriptomic profiles of Mandarin fish brain cells (CPB) infected with ISKNV and qRT-PCR. Standard curve of C_T value and plasmid copy number was drawn with standard plasmid pMD099, and the linear equation was:C_T=-3.42lgx+39.455, and the minimum detection limit was 3 copies/μL. Results of repeated trials showed variation coefficients of intra-and-inter groups were less than 2%, indicating the method has high sensitivity and repeatability. The ISKNV suspension was diluted into 10⁰–10³ copies/mL, and each T25 cell culture flask was inoculated with 1 mL virus diluted solution. Thereafter, total RNAs were extracted at 7, 9 and 11 d post inoculation. The mRNA of ORF099 gene was detected using routine qRT-PCR method. The results showed that the mRNAs of ISKNV could be detected from cells inoculated with one copy ISKNV virus at 7 days post inoculation. CPB cells have been inoculated with three batches of ISKNV inactivated by different concentrations (0.05%, 0.1%, 0.2%) of formaldehyde for 9 days. Results showed that ISKNV ORF099 mRNA was only detected from cells inoculated with 0.05% and 0.1% formaldehyde inactivated ISKNV at 7 days post inoculation by qRT-PCR. However, after blind passaging three generations, cells inoculated with ISKNV inactivated by 0.1% final concentration of formaldehyde did not exhibit CPE. The inactivated ISKNV did not cause clinical symptoms and death of fish, indicating this rapid virus inactivation test has higher sensitivity than cell blind passage trial and the fish safety test. The established method will be important for improving the ISKNV inactivated vaccine production.

Abstract:Tanichthys albonubes, which was listed as Class Ⅱ protected animal in China's State Key Protected Aquatic Animal List, is a typical representative of the small Danioninae fishes in South China. Aimed at understanding morphological differentiation between populations as well as providing scientific basis for developing conservation strategies of T. albonubes, we investigated the body-form variation using landmark-based geometric morphometric method among 8 wild populations and 2 hatchery populations of T. lbonubes. Frozen anesthetized fresh specimens were then fixed in 95% ethanol, a Nikon D-800 SLR camera was utilized to take standard images of the fixed specimens afterwards. Landmark coordinate values were extracted after samples digitized by image processing and processed by relative warp principal component(RW), grid deformation and discriminant analysis in TPS series software. The 24 RW were then identified using discrimination analysis to differentiate the ten T. lbonubes populations. The result indicated that, the 1 st, 2 nd and 3 rd RW accounted for 48.20%, 23.12% and 14.83% of the total variation respectively, of which type Ⅱ landmarks 12, 13, 14 and 15 had important contributions, and could explain the most variations. The most morphological variations were displayed in eye diameter and head shape. Furthermore, it uncovered obvious morphological variation among wild populations and hatchery populations. Therefore, we suggest that it should be forbidden to release the hatchery populations in filed. Given the results in this study and the punctate distribution of T. albonubes, we also proposal that the 7 wild populations (expect Vietnam) should be regard as 7 management units(MU), respectively.

Abstract:This paper described a kind of subunit vaccine, and the effect of Anabaena-expressed VP28 against white spot syndrome virus (WSSV) and the related immune response in Litopenaeus vannamei. Firstly, L. vannamei was orally administered by feeding Anabaena-expressed VP28 for 7 days. Secondly, the shrimp was challenged with WSSV and its mortality was monitored. Finally, the shrimp related immune index was measured. The results revealed that Anabaena-expressed vp28 can significantly improve the shrimp's ability against WSSV. The survival rate of feeding and immersing infected WSSV is 78.80% and 83.19% respectively. The results showed that oral agent can enhance the ability against WSSV in L. vannamei. After shrimp was administrated by Anabaena-expressed vp28, the shrimp enzyme acitivity at different time points showed that superoxide dismutase (SOD), phenoloxidase (PO), catalase (CAT), alkaline phosphatase (AKP) at 2 h after immunization were rising, and reached peak at 48 h or 96 h, which suggested that oral agent could cause the change of enzyme activity. The enzyme activity of shrimp hepatopancreas and muscle after feeding infection showed that the SOD activity of experimental group in hepatopancreas after challenge was 42.10%, 32.26% and 16.04% higher than those of the positive group, wide type group and blank group. In muscle, SOD activity was 17.70%, 11.50%, 15.00% and 10.00% higher than those of negative control, positive control, wide type and blank group after challenge. And the PO activity, CAT activity, and AKP activity of the experimental group were 12.17%, 88.80% and 240.07% higher than that of the positive control after challenge in hepatopancreas respectively. The PO activity, CAT activity, and AKP activity of the experimental group were 21.49%, 30.90% and 100% higher than that of wide type after challenge in hepatopancreas respectively. ACP activity was slightly higher than that of negative control, but ACP activity had no significant difference in the muscle groups. The results of shrimp PO, CAT, AKP and ACP activity of immersing infection were similar to feeding infection. The experiment group CAT and AKP activity after immersing infection is significantly higher than other groups, and the CAT activity of immersing infection were more significant than feeding infection. The PO activity of shrimp hepatopancreas of experiment group after immersing infection was significantly higher than those of positive control, wide type and blank, but ACP activity of different group was not significantly different. This paper showed that Anabaena-expressed vp28 can strengthen shrimp's resistance to WSSV and decrease the mortality of L. vannamei from white spot disease. The Anabaena-expressed vp28 can be drug and feed from the same feedstock without purification, which has great application potential for field use in large-scale production.

Abstract:In 1998, the orexin was independently discovered by two different laboratories, and it was latterly proved to have wide functions in feeding promotion, energy balance regulation, growth and reproduction in vertebrates. It is secreted and released from hypothalamus and can encode two peptides, orexin A and orexin B. They exhibit high conservation in sequence during evolution, and the prior research verified that they both have important functions in feeding regulation and energy metabolism in mammals and fish. Cynoglossus semilaevis is an important economic farmed flatfish and a favorite table fish in China. Its farming industry is expanding, however, the endocrine mechanisms underlying growth and feeding actions remain limited. To explore the possible endocrine mechanisms for food intake regulation of C. semilaevis, the matured peptide fragment of orexin B was amplified and subcloned into the prokaryotic expression vector pET-32a to successfully construct orexin B/pET-32a recombinant plasmid. The recombinant plasmid was high-efficiently expressed in E. coli BL21 strains after being induced by IPTG with special fusion polypeptides containing His6 at their N-terminus. The molecular weight of obtained orexin B polypeptide is 21.14 ku and maximally accounted for 43.5% of the whole bacterial protein post 6h induction with 1.0 mmol/L IPTG at 37℃. Western blotting analysis indicated that the recombinant polypeptides had the antigenicity to His6 antibody. The recombinant protein could be purified using Ni²⁺-NTA affinity chromatography. In vitro incubation of hypothalamus with recombinant expression orexin B of C. semilaevis indicated that it could promote the secretion and release of NYP peptide from hypothalamus, and upregulate the expression level of NPY mRNA. Meanwhile, the recombinant orexin B protein also could upregulate the expression level of orexin mRNA in hypothalamus at low concentration. All these verified that the obtained recombinant orexin B protein has biological activity in the present study. The present results would be helpful for better understanding the role of orexin B in feeding regulation and development of high-efficient feed additive for farming industry of C. semilaevis.

Abstract:

Abstract:Paraffin embedded tissue section and hematoxylin-eosin staining were used to investigate the morphological characteristics of smooth and striated adductor muscles in Crassostrea gigas. Muscle fibers were stained histochemically for NADH-diaphorase and adenosine triphosphatase activity (ATPase) to identify fiber types in smooth and striated muscles. The morphological characteristics of myofibers within smooth and striated muscles were compared by quantifying muscle diameter and cross-sectional area. Muscle fiber diameter in smooth muscle (5.97 μm) was significantly smaller than that in striated muscle (7.41 μm) (P<0.05). Muscle fiber density of smooth muscle (25 485.65±3917.807 n/mm²) was significantly higher than that in striated muscle (16 908.25±3917.807 n/mm²). The cross-sectional area of myofibers in striated muscle (40.45 μm²) was significantly greater than that in smooth muscle (26.25 μm², P<0.05). The result of NADH-TR histochemistry showed that the myofibers in smooth muscle were slow oxidative fibers (type I), as indicated by positive blue reat unstained by NADH-TR. ATPase histochemistry revealed that fibers in striated muscle were intensively stained and the fibers was type Ⅱ with a high ATPase activity. The fibers in smooth muscle were lightly stained or unstained, suggesting the fibers were type I. The results of ATPase/NADH-TR staining were consistent. In this study, we firstly illustrated the morphological characteristics of myofibers in smooth and striated adductor muscles of C. gigas, and compared the differences in contraction and metabolic profiles between smooth and striated muscles. This research not only provides important information for in-depth studies on biological characteristics of muscle fibers in C. gigas, but also provides theoretical basis for improving the meat quality of molluscs.