Dkkl1 gene plays an important role in mammalian testicular development and spermatogenesis, but the research of Dkkl1 gene in turtles is still limited. Therefore, in order to explore its potential function and mechanism of action in turtles, we cloned a cDNA fragment of Dkkl1 gene from Chinese soft-shelled turtle (Pelodiscus sinensis), and analyzed its sequence characteristics, expression pattern and response to exogenous hormone treatment. The cDNA of Dkkl1 gene was 823 bp in length, with 3' UTR of 67 bp, 5' UTR of 90 bp, open reading frame of 666 bp, and encoded 222 amino acids in total. Dkkl1 protein is a kind of alkaline protein with poor stability and high hydrophilicity. The secondary and tertiary structures of Dkkl1 protein are mainly dominated by α-helix and irregular coil. Amino acid sequence homology comparison showed high similarity with Chinemys reevesii Dkkl1 protein (81%), but low homology with Dermochelys coriacea Dkkl1 protein (70%). RT-PCR and RT-qPCR analyses reveal that Dkkl1 mRNA was significantly highly expressed in spermathecae of 3-winter-age P. sinensis adults (P<0.001), while it was hardly expressed in the rest of somatic tissues. Moreover, the expression of Dkkl1 gene in P. sinensis spermathecae gradually increased with age and peaked at 3-winter-age. In addition, both 17β-estradiol and 17α-methyltestosterone treatments significantly inhibited the expression of Dkkl1 gene in adult P. sinensis spermathecae (P<0.05). The results suggest that the Dkkl1 gene might play an important role in the process of testicular development and spermatogenesis in P. sinensis.
To explore the early embryonic development process of bullfrogs (Rana catesbeiana) and supplement their biological information and imaging data, we obtained the fertilized eggs from artificially bred bullfrogs by natural oviposition to investigate their morphological changes and biological characteristics. The results show that the size of fertilized eggs was (1.41±0.31) mm. At temperature of (24.5±0.4) ℃, the early embryonic development process could be divided into 7 phases and 24 stages. It took 177 h 38 min for the fertilized eggs to reach the operculum closure stage, and the total accumulated temperature was 4 249.71 h·℃. The embryonic development process showed a pattern of a fast speed at the first several stages (From fertilized egg to 64-cell stage) and then a slowdown at the latter stages. When being stimulated by external stimuli, the embryo had an annular contraction response by bending the head and tail. Later, as the embryo hatched until the completion of gill closure, they become tadpoles.
Yangtze sturgeon (Acipenser dabryanus) is an endemic fish in China and has been listed as a critically endangered (CR) species by the International Union for Conservation of Nature (IUCN). In order to provide a reference basis for healthy breeding and disease analysis of juvenile Yangtze sturgeon, we analyzed the composition, diversity and dynamic changes of microbial flora between its surface mucus, intestinal content and culture water by using Illumina high-throughput sequencing technology. The results show the diversity of microorganisms in culture water was higher than that in mucus and intestinal content. The microbial community structure of mucus and intestinal content were more similar, and could be clearly distinguished from the microbial community of culture water. On phylum level, mucus and intestinal content were mainly composed of Actinobacteria, Proteobacteria and Firmicutes, while the culture water was mainly composed of Proteobacteria, Bacteroidetes and Firmicutes. Seven potential pathogenic genera were found, mainly in culture water and mucus which might lead to the occurrence of diseases under certain circumstances. BugBase phenotype prediction analysis reveals that both Gram negative and Gram positive bacteria were present in the mucus, intestinal content and culture water of juvenile Yangtze sturgeon. The dominant microbiota of intestinal content was Gram positive bacteria, accounting for over 60%. The dominant microbial communities in mucus and culture water were both Gram negative bacteria, accounting for 60% and 70%, respectively. In terms of oxygen demand, mucus and intestinal content were mainly composed of aerobic bacteria, while culture water was mainly composed of aerobic and facultative anaerobic bacteria.
Ammonia (NH4+-N), nitrate (NO3−-N) and nitrite (NO2−-N) are the main contaminants in industrial aquaculture systems. High nitrogen concentration in water is likely to cause aquaculture water pollution and endanger the safety of aquatic animals. Aerobic denitrifying bacteria are widely used to remove nitrogen-containing aquaculture wastewater. In order to obtain a strain that can safely and efficiently treat wastewater with high ammonia nitrogen concentration, we studied the aerobic denitrifying bacteria WM28 with high ammonia nitrogen resistance screened from aquaculture ponds. The strain was identified through morphological observation, physiological and biochemical tests and 16S rRNA gene sequencing. The environmental and biological safety of the strains were evaluated through antibiotic tests and zebrafish (Danio rerio) toxicity tests. The growth and denitrification performance were measured in three single nitrogen source simulated wastewater, and the denitrification capacity was tested in high concentration ammonia nitrogen simulated wastewater. WM28 was identified as Rhodococcus ruber with high antibiotic sensitivity and good biosafety. The removal rates were 100%, 76.3% and 66.99% after 48 h incubation in single NH4+-N, NO3−-N and NO2−-N media, respectively. Their removal rates of NH4+-N reached 100% at high concentrations of 100–500 mg·L−1 NH4+-N in simulated wastewater experiment after 48 h. 700 mg·L−1 NH4+-N was removed by more than 88% after 116 h. At 120th hour, the initial NH4+-N concentration of 1 000 mg·L−1 was still capable of denitrification with a removal rate of 74.38%, which indicates that strain WM28 has great tolerance to high ammonia nitrogen. In summary, strain WM28 is a safe and efficient aerobic denitrifying bacteria with high ammonia tolerance, and has promising application prospects in the treatment of aquaculture and industrial wastewater.
Development of sea cucumber larvae needs to go through stages of auricularia, doliolaria, pentactula and juvenile. High mortality rate from metamorphosis and development of planktonic larvae to attachment stage of seedlings is a common problem in tropical sea cucumbers breeding. However, the gene regulation mechanism underlying the metamorphosis development of tropical sea cucumber is still unclear. In this study, we chose larval Holothuria leucospilota from four periods of early auricularia (A), mid auricularia (B), late auricularia (C) and doliolaria (D) as samples for high-throughput transcriptome sequencing to investigate the molecular mechanism underlying its metamorphosis development. The results show that a total of 83.6 GB Raw reads were generated, and 93 528 Unigenes were obtained by splicing. Pairwise comparisons between adjacent groups of the four sequencing libraries show that the number of genes with significant differential expression in A_vs_B, B_vs_C and C_vs_D were 17 732, 11 757 and 11 319, respectively. GO function enrichment shows that differential genes were mainly enriched in GO functions related to cell growth, such as molecular function and catalytic activity. In addition, KEGG pathways were analyzed, and the results show that the differential genes were significantly enriched in pathways related to cell differentiation, proliferation and apoptosis, such as PI3K-Akt, cell cycle and cancer pathways. Among them, the enrichment frequency of the pathway in cancer significantly increased during the metamorphosis process, which indicates a key role in the transformation of larval growth and development mode. The screened differentially expressed genes and predicted functional information can lay a foundation for the research on the regulatory mechanism of growth and development, artificial breeding and molecular improvement application of H. leucospilota.
Mystus macropterus is a high-quality aquaculture variety that urgently needs to be developed. Exploring the characteristics and patterns of early developmental stages of cultured M. macropterus can provide basic data for its seedling cultivation and large-scale efficient seed production. We studied the morphological characteristics and developmental features of its embryos and juveniles by microscopic observation, and measured the morphological indicators to derive regression equations for the growth characteristics of juveniles. The results show that the fertilized eggs of the fish were oval and yellowish brown, with a diameter of (3.46±0.3) mm. At incubation temperature of 26.2 ℃, the embryos took 79 h to develop for eight stages with 28 periods, including fertilization, cleavage, blastocyst, gastrula, neuroembryo, organ differentiation and hatching, and the total accumulative temperature was 2065.26 h·℃. The total length of the larvae was (7.31±0.52) mm, the larvae stage lasted for 10 d, and most of the yolk sac was absorbed at early stage of larvae. The full-length specific growth rate (SGRL) was 9.79%, and the weight-specific growth rate (SGRm) was 12.31%. Most of the larvae opened 7–8 d after membrane emergence, and the yolk sac disappeared on 9th day. The SGRL and SGRm were 4.15% and 12.25% at later stage of larvae, respectively. The juvenile stage lasted for 11 d. The fins were basically mature, and the body size and body color were close to those of adult fish. SGRL was 4.30%, SGRm was 13.17%, and the total length was 22–24 mm. The statistical model shows that the growth of the larvae and juveniles is of allometric type.
Sargassum ilicifolium is the dominant species in the coastal seaweed field of Hainan Island. To provide technical support for the protection and restoration of seaweed field, we studied the physiological and ecological adaptability of S. ilicifolium by using chlorophyll fluorescence technology in addition with analysis of changes in photosynthetic pigment content and growth rate under different growth conditions. At different temperatures (10, 14, 18, 22, 26 and 30 ℃), light intensities (10, 20, 40, 80, 120 and 200 µmol·m−2·s −1) and salinities (20‰, 24‰, 28‰, 32‰, 36‰ and 40‰), we measured the specific growth rate, chlorophyll content and maximum fluorescence yield (Fv/Fm) of S. ilicifolium. The results show that the optimal temperature for the growth of S. ilicifolium was 18–26 ℃; the optimal light intensity was 20–120 µmol·m−2·s−1; the optimal salinity was 16‰–36‰. These results indicate that S. ilicifolium is a temperature-loving macroalgae and is more sensitive to low temperature stress. Too low or too high light intensity will lead to algal damage. Therefore, the effects of temperature and light intensity on the growth and spatial distribution should be fully considered in the process of conservation and restoration of the seaweed fields dominated by S. ilicifolium. These results indicate that S. ilicifolium is a temperature-loving macroalgae and is more sensitive to low temperature stress. Too low or too high light intensity will lead to algal damage. Therefore, the effects of temperature and light intensity on the growth and spatial distribution should be fully considered in the process of conservation and restoration of the seaweed fields dominated by S. ilicifolium.
Skipjack tuna (Katsuwonus pelamis) is widely distributed in tropical and subtropical waters around the world and is a key target species in global tuna fishery. The abundance of its resources is influenced by various marine environmental factors. In order to explore the mechanisms by which precipitation affects the distribution and variation of resources in different K. pelamis stocks, based on the data from the pair trawl fishery in Mauritanian waters during 2017−2019, data from the purse seine fishery from the Western and Central Pacific Ocean during 2018−2020, and data from the longline fishery recorded on the IATTC website during 2010−2020, combining with environmental data such as precipitation, sea surface salinity (SSS) and sea surface temperature (SST), we analyzed the spatiotemporal distribution of catch per unit effort (CPUE) for three different fishing methods of skipjack tuna and its relationship with environmental factors such as precipitation by Generalized Additive Model (GAM). The findings indicate that month significantly influenced the CPUE of skipjack tuna for pair trawl and longline fishing methods (P<0.05). Latitude also had a significant effect on all the three fishing methods (P<0.05). Precipitation exhibited an extremely significant effect (P<0.001) on the CPUE of skipjack tuna for pair trawl fishing method and a significant effect (P<0.05) for purse seine fishing method. The trend of this effect was relatively consistent, with higher CPUE occurring within a more suitable range of precipitation. However, the effect of precipitation on the CPUE of skipjack tuna for longline fishing method was not significant. Sea surface salinity and sea surface temperature also had significant effects on the CPUE of skipjack tuna for all the three fishing methods (P<0.05). Hence, when analyzing the effects of environmental factors on fishery CPUE in the future, it is recommended to include precipitation in conventional marine environmental factors.
To evaluate the gastrointestinal effects of Amomum villosum essential oil on promoting digestion and protecting intestine tract in breeding of Oreochromis niloticus, we fed the juveniles [(20.34±2.08) g] with basic diets of 0 (Control group), 2 (Low-dose group), 4 (Medium-dose group) and 8 g·kg−1 (High-dose group) of A. villosum essential oil for 8 weeks. The results show that with the increase of essential oil concentration: 1) The final body mass, final body length, weight gain rate and specific growth rate increased first and then decreased, but the feed conversion ratio (FCR) decreased first and then increased. The growth indexes of the low dose group were better than those of the other groups (P<0.05). 2) The activities of pepsin, gastric amylase, intestinal amylase and intestinal lipase in each group increased first and then decreased, and the activities of digestive enzymes increased significantly in the low dose group (P<0.05). 3) The activities of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT), concentrations of glutathione (GSH) and malondialdehyde (MDA) in the intestine increased first and then decreased, and the difference in the low-dose group was significant (P<0.05). 4) In serum, the concentrations of total protein (TP), globulin (GLOB), total cholesterol (TC), triacylglycerol (TG), low density lipoprotein cholesterol (LDL-CH) and high-density lipoprotein cholesterol (HDL-CH), as well as activities of alanine aminotransferase (ALP) and alanine aminotransferase (ALT) decreased first and then increased. The concentrations of TP, GLOB, TC, LDL-CH and HDL-CH in the low-dose group decreased significantly (P<0.05). To sum up, adding 2 g·kg−1A. villosum essential oil into basic diet can improve the digestive capacity, intestinal antioxidant capacity and serum biochemical indexes of juvenile tilapia and promote their growth performance.
In order to evaluate the reasonable dosage and safety of copper (II) sulfate, metrifonate and povidone-iodine, which are commonly used in aquaculture, and their toxic effects on GIFT tilapia (Oreochromis niloticus), we tested their acute toxicity and histopathological effects on GIFT tilapia under hydrostatic conditions. The results show that the LC50s (24, 48 and 96 h) of copper sulfate were 13.715, 10.351 and 5.896 mg∙L−1, respectively, and the safety concentration was 1.769 mg∙L−1. The LC50s (24, 48 and 96 h) of trichlorfon were 43.036, 25.887 and 16.689 mg∙L−1, respectively, and the safety concentration was 2.810 mg∙L−1. The LC50s (24, 48 and 96 h) of povidone iodine were 10.509, 9.301 and 8.674 mg∙L−1, respectively, and the safety concentration was 2.190 mg∙L−1. Histopathological observation suggests that copper sulfate exposure can cause blurred gill filament outline, vacuolation of gill tissue, enlargement of liver tissue gap, vacuolation and nuclear atrophy, damage of nerve fibers in brain tissue, cell apoptosis, damage of renal tubular structure and nuclear membrane. Trichlorfon exposure can cause gill tissue damage and cell apoptosis, liver tissue denuclearization, mitochondrial swelling and vacuolation, brain tissue nerve fiber damage, nuclear pyknosis and renal interstitial hemorrhage. Exposure to povidone iodine can cause atrophy of gill filaments, incomplete structure of mitochondrial bilayer membrane, vacuolation of liver tissue, apoptosis of cells, and slight damage of nerve fibers. In conclusion, copper sulfate, trichlorfon and povidone iodine are relatively safe drugs for tilapia, but their dosage should be carefully controlled to avoid irreversible tissue damage.
Compared with ozone gas and ozone water, ozone ice not only maintains the original characteristics of ozone, but also shows higher ozone stability, better preservation effect and more convenient use. In this study, in order to explore methods for preparing high concentration ozone ice and improving ozone preservation rate, we used an ozone water integrated machine circulation device to prepare high-concentration ozone water. By adjusting the flow rate of ozone gas in ozone water integrated machine, the water temperature and pH in the circulating water tank, we determined the optimal conditions for preparing high-concentration ozone water. Then we used high concentration ozone water to prepare ozone ice, exploring methods for preparing high concentration ozone ice and improving ozone preservation rate by changing the preparation conditions and storage methods of ozone ice. The results show that ozone water of 50.27 mg·L−1 can be prepared in a short time by fixing the flow rate of ozone gas of 3 L·min−1 and adjusting the water temperature to 5 ℃ in circulating water tank and at pH of 3. Ozone ice with an ozone retention rate of 58.13% can be prepared by using liquid nitrogen to freeze high-concentration ozone water at temperature of 5 ℃ and pH of 5. In addition, the stability of ozone ice can be effectively improved by adding acetic acid as acidity regulator of ozone ice and storing the ozone ice at −40 ℃.
As the primary producer of river ecosystem, the dynamic changes of phytoplankton are related to the stability of fishery resources and water ecosystem. We investigated the community structure of phytoplankton in three typical sections of the Pearl River in dry season (March), wet season (July) and level season (November) in 2021, and evaluated the current situation of water quality by biodiversity and other indicators, so as to provide technical support for the Pearl River water pollution control and water ecological restoration. Results indicate that the species composition, abundance and dominant species of phytoplankton showed significant spatiotemporal changes (P<0.05). A total of 187 species were identified throughout the year (117 in March, 98 in July and 77 in November). The average cell abundance of phytoplankton was 8.6×105, 72.1×105 and 4.0×105 cells·L−1 , and the biomass was 1.235 4, 4.674 5 and 0.569 8 mg·L−1 in March, July and November, respectively. The abundance of Cyanophyta reached 1.18×107 cells·L−1 (Slight cyanobacteria bloom level) in Shijiao section of the Pearl River in wet season. The phytoplankton community structure in the upper reaches of the Pearl River changed from chlorophyta type in dry season to chlorophyta-cyanobacteria type in wet season, and Scenedesmus quadricauda, Merismopedia tenuissima and S. armatus var. boglariensis f. bicaudatus were the dominant species throughout the year. In the lower reaches, the phytoplankton community structure changed from diatomic type to diatom-cyanobacteria type, with Melosira granulata and M. tenuissima as the dominant species. Shannon-Wiener index (H'), Pielou index (J') and Margalef index (D) were 1.58–3.05, 0.51–0.84 and 1.60–3.42, respectively. According to the comprehensive evaluation based on the biodiversity indexes, the water quality in the three typical reaches of the Pearl River was between mild pollution and α-medium pollution, and the water quality still needs to be improved.
In order to solve the problems in paternity test and genealogical management for improved variety breeding of Monopterus albus, we obtained 16 microsatellite markers with high polymorphism through whole genome searching of and following confirmation, and established two multiplex PCR sets by using 16 high polymorphic microsatellite markers and successfully applied to the parentage assignment for 11 full-sib M. albus families. The average allele number(Na) of 16 microsatellite was 5.562; the average of abserved heterozygosite(Ho) was 0.627; the average of expected heterozygosite(He) was 0.619; the average of polymorphic information content (PIC) was 0.564. Parentage analysis reveals that the combined exclusion probability of first parent given only the genotype of the offspring (CE-1P) was 0.999 999 99, the combined exclusion probability of a second candidate parent given the genotype of the offspring and one known parent (CE-2P) was 0.999 999 91, and combined exclusion probability of a parent pair given only the genotype of the offspring (CE-PP) was 0.999 964 76. The simulated identification rate of the 11 M. albus families was 99.96%, and the actual identification rate was 95%. Furthermore, the simulation analysis shows that the identification rate could reach over 95% in the case of 200 candidate parental individuals with known sexes and 150 candidate parental individuals with unknown sexes. The cluster analysis shows that 108 offspring could be clustered correctly except two, and the accuracy rate was 98.18%. The paternity method of M. albus established in this study provides important technical support for the future breeding program and management of germplasm resources of M. albus.
Lewis antigen is regarded as a specific binding receptor for norovirus, and Lewis-like antigen is also present in oysters as a vehicle for norovirus transmission, but the pathway for synthesis of this carbohydrate in oysters has not been elucidated. To clarify the pathway of norovirus receptor-like Lewis antigen synthesis in oysters, we cloned the CgFUT5 gene from Pacific oyster (Crassostrea gigas) genome and analyzed the expression in five tissues. The full sequence of CgFUT5 gene was obtained by rapid amplification of cDNA ends (RACE) and bioinformatically analyzed by real-time quantitative polymerase chain reaction (RT-qPCR). A prokaryotic expression plasmid was constructed to transform Escherichia coli for heterologous expression, and immunogenicity was identified by immunoblotting (Western blot). The cDNA sequence of CgFUT5 gene with 1 173 bp open reading region was obtained by cloning, and phylogenetic tree shows that CgFUT5 gene was genetically related to the rockweed glycosyltransferase gene that had the function of synthesizing Lewis antigen in several species. The recombinant CgFUT5 protein could be overexpressed in E. coli, and the expressed recombinant CgFUT5 protein specifically bound to both anti-human FUT5 antibody and anti-6×His tag antibody. To sum up, CgFUT5 gene was successfully cloned and found to be abundantly expressed in oyster gill tissue, and CgFUT5 protein has similar immunogenicity to human FUT5 protein. It is hypothesized that a Lewis-like antigen synthesis pathway exists in oysters, and the genes regulating Lewis-like antigen synthesis in oysters also have differential tissue expression.
To compare the otolith morphology of different Larimichthys polyactis populations, and to further clarify their population division, we applied the landmark method better at extracting morphological features for the first time, to explore the morphological differences of otoliths from L. polyactis populations in the Southern Yellow Sea and East China Sea. From March to December 2022, 30 individuals of 1-year old fish had been collected from each from Haizhou Bay (HZB), Lyusi (LS), Yangtze Estuary (YTE) and Zhoushan (ZS) fishing grounds. After extracting the left sagittal otoliths, we seclected even landmarks in otolith contour and four landmarks in sulcus acusticus for the landmark analysis. Results show that: 1) Among the 11 landmarks, those in sulcus acusticus (Landmark 8−11) had main contribution (91.88%) in explaining the main source of morphological variation, while those in otolith contour (Landmark 1−7) just had 8.12%, which reveals that the differences in otolith morphology among the four geographical groups mainly came from the auditory sulcus of otolith. 2) According to the scatter plot of principal component analysis, part of the Haizhou Bay population was significantly divided into one group, while the remaining Haizhou Bay fishing grounds and all other three fishing grounds had highly overlapped and clustered into another group, indicating that there might be two L. polyactis populations in the Southern Yellow Sea area, namely the Southern Yellow Sea-East China Sea group and the Northern Yellow Sea-Bohai Sea group. This also indicates that there were mixed L. polyactis populations in the Haizhou Bay fishing grounds. This may be explained by the long-term egg and larval dispersal process controlled by the current and active migratory routes during feeding and overwintering period. The results verified the potential of otolith morphology in delineating the populations of L. polyactis, providing valuable references for their spatiotemporal distribution.
In order to explore the synergistic effects of acidification and environmental pollutant phenanthrene (PHE) on Chinese mitten crabs (Eriocheir sinensis), we carried out a 14-day joint exposure experiment of E. sinensis [(15.0±2.3) g] to different pH (5.5, 6.5, 7.8) and PHE (0, 50 µg·L−1). The results show that: 1) Under the synergistic treatment of pH 5.5×PHE 50 on E. sinensis, the hepatopancreas and gill tissues were severely damaged; the shape of the hepatopancreatic tubules changed; a large number of vacuoles appeared in the atrophy of the hepatic duct cells. The gill axis was enlarged; the cuticle of the gill filament was damaged; the local basement membrane was ruptured. However, pH 6.5×PHE 50 did not significantly damage the hepatopancreas and gill tissues of E. sinensis. 2) PHE treatment significantly reduced the contents of Gly and LDL-C in hepatopancreas of juvenile E. sinensis, indicating that PHE could decrease the energy metabolism level of E. sinensis. Compared with the control group, pH 5.5×PHE 50 inhibited the contents of TG, Gly, HDL-C and LDL-C, while pH 6.5×PHE 50 significantly increased TG content. 3) Real-time fluorescent quantitative PCR experiment shows that AHR, ARNT and CYP1A1 increased significantly with the decrease of pH, and reached the highest values at pH 5.5. The results reveal that the combining effect of acidification and PHE changes the energy metabolism of E. sinensis, and pH 5.5 significantly aggravates the toxic effect of PHE on the hepatopancreas tissue structure of E. sinensis, as well as its energy metabolism.
In order to explore the suitable breeding density and effective culture mode of Tapes dorsatus in three sea areas of Beibu Gulf, Guangxi, we had carried out basket nursery culture, basket adult culture and net cage hanging experiments of T. dorsatus in mudflat of three sea areas in Qingzhou, Beihai and Fangchenggang from May 2021 to January 2023. The results show that: 1) The suitable nursery culture density for T. dorsatus were 2 000, 1 500 and 1 500 grains·basket−1, respectively, and the growth indexes and survival rate of T. dorsatus decreased with the increase of nursery culture density. The survival rates of all density groups in Beihai were significantly better than those in Fangchenggang and Qinzhou (P<0.05). Except that the growth indexes (Shell length, shell width and body mass) in d5 group (3 000 grains·basket−1) in Beihai were lower than that in Fangchenggang, the growth indexes of other groups were all higher than those of Fangchenggang and Qinzhou. 2) The suitable culture densities of T. dorsatus in Beihai, Fangchenggang and Qinzhou were 40, 40 and 20 grains·basket−1, respectively. The growth indexes and survival rate of T. dorsatus at adult stage were Beihai>Fangchenggang>Qinzhou, and the survival rate decreased with the increase of cultivation density. When the density of net cage suspension in Fangchenggang was 30 grains· cage−1, all growth indexes were the highest. There were no significant differences in shell length, shell width, shell height, body mass and survival rate among different density groups in net cage suspension (P>0.05). The results of environmental factors show that the water temperature, beach temperature, salinity, transparency, pH and DO in Beihai were slightly higher than those in Fangchenggang and Qinzhou, with relatively stable water quality. The water quality environment in Qinzhou and Fangchenggang changed greatly and was unstable. The diameter of plasmid at the bottom of Beihai mudflat was mainly coarse sand (49.00%), Fangchenggang was mainly composed of medium sand (59.28%), and Qinzhou was mainly composed of fine sand (77.33%). The results of phytoplankton quantity show that the species and quantity of phytoplankton algae in Beihai were the largest, and the least species and quantity of phytoplankton algae were in Qinzhou. The research indicates that T. dorsatus is suitable for nursery and adult culture in three sea areas of Beibu Gulf, and the breeding effect in Beihai is better than that in Fangchenggang and Qinzhou. Besides, 1.5-year-old T. dorsatus is suitable for net cage hanging culture in Fangchenggang sea area.
In order to study the adhesion characteristics of fouled organisms on different materials of mesh, we had carried out on-site hanging experiments of ultra-high molecular weight polyethylene mesh and copper alloy mesh in the waters of Nanri Island, Putian City, Fujian Province during March−May 2022 (Spring) and June−August 2022 (Summer). The results reveal that the attachment of the two kinds of fouled organisms showed certain seasonal differences. The compactness, quantity of species, quantity of dominant species, wet mass and density of the two net-coated stained organisms were lower in spring than in summer. In spring and summer, for ultra-high molecular weight polyethylene mesh, the average compactnesses were 47.19% and 86.98%, respectively; the average wet masses of fouling organisms were (144.83±15.69) and (1 054.59±34.81) g·net−1, respectively; the average densities were (2 699±49) and (4 630±53) ind·net−1, respectively; the quantities of species were 12 and 35, respectively; the quantities of dominant species were 4 and 6, respectively. In spring and summer, for copper alloy mesh, the average compactnesses were 41.04% and 74.95%, respectively; the average wet masses of fouling organisms were (118.32±20.13) and (876.25±23.16) g·net−1, respectively; the average densities were (2 678±42) and (3 870±64) ind·net−1, respectively; the quantities of species were 12 and 19, respectively; the quantities of dominant species were 3 and 4, respectively. The compactness, quantity of species (The same in spring), quantity of dominant species (The same in spring), wet mass and density of ultra-high molecular weight polyethylene mesh were higher than those of copper alloy mesh in spring and summer. The change of seawater temperature is the main reason for the seasonal difference of fouling organisms, and the anti-fouling biological adhesion effect of copper alloy mesh is better than that of ultra-high molecular weight polyethylene mesh.
