Abstract:The complement system is an evolutionary and crucial component of the innate immune response, which is key to detecting and removing invading pathogens. C1q-domain-containing proteins (C1qDC), as the first subcomponent of the classical pathway in the complement system, can bind immune complexes and activate the classical pathway. Although recent advances in many species have reported the characterization and functional roles of C1qDC in innate immunity, systematic knowledge of C1qDC is still lacking in Pinctada fucata. In this study, the phylogenetic relationship, sequence structure, motif composition, chromosome location, and expression pattern of identified C1qDC genes from the sequencing data of the whole genome of P. fucata were analyzed. The results showed that 285 C1qDC genes were identified and divided into five groups. C1qDC genes have been studied in many species, but the transcript number varies greatly among different species. In previous studies, 232, 335, and 476 C1qDC genes were identified in Mytilus galloprovincialis, Crassostrea gigas, and Crassostrea virginica, respectively. The transcript numbers are far more than that of C1qDC genes in fish and humans, and this is likely related to the lack of adaptive immunity of invertebrates and a weak ability of bivalves to resist adverse external environment and pathogens. The massive gene family expansion has occurred in bivalve evolution and is also common in the bivalve genomes. Structure analysis revealed that all the C1qDC proteins of P. fucata contained motif 1 and were randomly distributed on 14 chromosomes. Additionally, 68 pairs of tandem duplication and one pair of segmental duplication events were found. The higher synonymous substitution rate relative to the non-synonymous rate observed in P. fucata evoked C1qDC genes to evolve under purification selection. Some C1qDC genes showed high levels of polymorphism and were driven by selective pressure to fight off the noxious pathogens. Adaptive evolution of sequence polymorphism likely reflected the coevolution or interplay of host and pathogen. Recent research showed that C1qDC mainly functions as a pattern recognition receptor to mediate cell phagocytosis and agglutination via directly interacting with the receptor on the cell outer membrane. According to the transcriptome data, 56 C1qDC genes (32 upregulated and 24 downregulated) were significantly differentially expressed after the Vibrio alginolyticus challenge. Additionally, real-time PCR was implemented for eight randomly selected C1qDC genes, and agreement was confirmed between the high-throughput sequencing and real-time PCR data. The expression of the C1qDC genes increased in the hemocytes of P. fucata, which indicated that C1qDC might be involved in the immune response related to V. alginolyticus infection. These results provide a theoretical basis for further analysis of the evolutionary pattern of the C1qDC genes and the regulatory roles in the immune response in bivalves.

Abstract:Osteoglossidae, a family of ancient fishes known as “living fossils,” has high economic, cultural, and scientific value. In this study, we analyzed the molecular phylogeny of higher-order elements in the Osteoglossidae family using ribosomal DNA sequences. The complete sequences of the ribosomal gene of Arapaima gigas, Heterotis niloticus, Osteoglossum bicirrhosum, O. ferreirai, Scleropages formosus, S. jardinii, and S. leichardti, obtained using second-generation and third-generation sequencing methods, were as follows: 11714 bp, 8957 bp, 12057 bp, 11556 bp, 10377 bp, 10724 bp, and 10725 bp, respectively. The base content of GC ranged from 63.78% to 66.13%. The lengths of 18S rDNA were 1835 bp; GC content ranged from 54.06% to 54.5%. The genetic distance ranged from 0.000 to 0.024, and the sequence identity varied from 97.52% to 100%. The lengths of ITS1 rDNA were between 598 bp and 871 bp; GC content ranged from 72.6% to 78.3%. The genetic distance ranged from 0.000 to 0.852, and the sequence identity varied from 38.34% to 99.5%. The lengths of 5.8S rDNA were 159 bp; GC content ranged from 57.23% to 57.86%. The genetic distance ranged from 0.000 to 0.019, and the sequence identity varied from 98.11% to 100%. The lengths of ITS2 rDNA were between 327 bp and 612 bp; GC content ranged from 70.34% to 80.07%. The genetic distance ranged from 0.000 to 0.799, and the sequence identity varied from 31.63% to 99.53%. The lengths of 28S rDNA were between 3996 bp and 4419 bp; GC content ranged from 62.42% to 65.69%. The genetic distance ranged from 0.000 to 0.066, and the sequence identity varied from 84.98% to 99.95%. The lengths of IGS rDNA were between 1815 bp and 4679 bp; GC content ranged from 63.73% to 71.52%. The genetic distance ranged from 0.001 to 1.877, and the sequence identity varied from 19.31% to 98.31%. The phylogenetic tree was constructed using the neighbor-joining method and Bayesian inference method on the 18S, ITS1, ITS2, and 28S single sequences and the 18S+ITS1+5.8S+ITS2+28S combined sequence. The results showed that the topological structure of the two trees was consistent. Moreover, this result is concordant with the traditional classification of seven species of bony tongue fish, except for ITS1, which can be used as a molecular marker of Osteoglossidae. Our findings provide data for the phylogenetic study of ancient fishes and to enrich the diversity and evolution mode research of fish using ribosomal RNA genes.

Abstract:To explore the regulation of lysophosphatidylglycerol acyltransferase (LPGAT) expression patterns during the ovarian development of Eriocheir sinensis, the open reading frame (ORF) sequence of Es-lpgat1 of E. sinensis (accession number: MZ312613) was cloned. Then, its temporal and spatial expression patterns during ovarian development were analyzed using real-time quantitative polymerase chain reaction (qRT-PCR), in situ hybridization, and RNA interference. The results showed that the ORF of Es-lpgat1 was 1125 bp in length, en-coding a 374-amino acid protein with a molecular weight of 44 kD. It belonged to the LPGAT superfamily, and the amino acid sequence deduced from Es-lpgat1 exhibited the highest identity with Portunus trituberculatus. qRT-PCR results showed that Es-lpgat1 was expressed in different tissues during the ovarian development of E. sinensis, with the highest expression in the ovary and the lowest level in the gills (P＜0.05). During the ovarian development cycle, both the hepatopancreas and ovary at ovarian stage II presented the highest expression levels of Es-lpgat1mRNA (P＜0.05), and there was a significant increasing trend during the period from ovarian stage III to stage V. The results of in situ hybridization showed that in ovarian stage II, the strong signal of Es-lpgat1 mRNA was localized in the cytoplasm of previtellogenic oocytes and endogenous vitellogenic oocytes of the ovary, while a very weak signal was detected in stage IV ovaries. However, a strong signal of Es-lpgat1 mRNA was localized in fibrillar cells (F cells) and resorptive cells (R cells) of hepatopancreas at stages II and IV. After knockdown of Es-lpgat1, the expression levels of Es-gpat2 and Es-dgat2 were significantly up-regulated, while the expression levels of Es-agpat4 and Es-dgat1 were significantly down-regulated. In summary, Es-lpgat1 mRNA was mainly expressed in the ovary and hepatopancreas of E. sinensis, which was significantly related to the ovarian stages. These results suggested that Es-lpgat1 may be involved in phospholipid metabolism during ovarian development of E. sinensis.

Abstract:The breeding array is currently the most popular genotyping tool and has played an important role in crops and livestock breeding. In the aquaculture industry, many genotyping arrays have been developed and applied to the genetic breeding of important aquaculture species. The large yellow croaker (Larimichthys crocea) industry in China is threatened by numerous problems, such as germplasm degradation and frequent diseases. It is urgent to overcome the current development bottleneck through breeding, and a stable breeding array is needed. In this study, a breeding array named “Ningxin-2” is developed based on the high-throughput single nucleotide poly-morphism (SNP) array “Ningxin-1.” The “Ningxin-2” array selects representative SNP sites in the haplotype block of large yellow croakers and integrates SNP sites that are associated with cryptocaryon resistance and high-temperature tolerance of the large yellow croaker. The “Ningxin-2” breeding array integrates 54077 high-quality SNP sites evenly distributed in the large yellow croaker genome. Evaluation of “Ningxin-2” in 756 large yellow croakers from six populations shows that the call rate of the array is above 98.4%, and the proportion of polymorphic SNP is above 91.2%. The “Ningxin-2” is stable, accurate, and cost-efficient, and it is expected to play an important role in research for targeted genetic improvement and genomic selection of large yellow croakers.

Abstract:Triplophysa yarkandensi is an indigenous fish in the Tarim River in Xinjiang Province. To accumulate theoretical breeding data for T. yarkandensi, the effects of morphological traits on body weight were explored. Body weight (Y) and nine morphological traits were measured, including the total length (X₁), body length (X₂), body height (X₃), head length (X₄), tail stalk length (X₅), snout length (X₆), eye length (X₇), interorbital space (X₈), and slit width (X₉). Correlation analysis, path analysis, and regression analysis were used to determine the three main morphological traits that affect body weight (Y). The best-fitting model for the three main morphological characters and body weight was determined by curve fitting. Overall, there was a significant positive correlation between body weight and morphological traits (P＜0.01); the length of the tail stalk, eye diameter, and eye distance were not related to each other (P＞0.05). There were multiple collinear relationships between other traits and body weight; head length had the most direct effect on body weight (0.470), and body length had the most indirect effect on body weight (0.447), although head length and body length were the main variables that affected body weight. Head length was the largest direct determinant of body weight (0.221), and the largest co-determination coefficient of body length and head length was 0.341. The sum of the determinants of body weight (Y) for the three morphological traits was 0.958, which explained 95.8% of the variation. The linear equation for the three main morphological traits and body weight was Y=–2.8+2.94X₂+0.764X₄+0.906X₅ (R² =0.958). The optimal model equations for the three main morphological traits and body weight contained exponential functions, a power function, and a linear function, and the model equations were Y=2.739e^0.158X2 (R² =0.936), Y=4.946X₄ ^1.100 (R₂ =0.931), and Y=9.582+8.876lnX₅ (R² =0.807) for the curve equation for the tail stalk length and body weight (Y). This indicated that the tail stalk length was not a main morphological factor and was the only variable that could not explain the change in body weight. Body length and head length were the main selection traits, and tail stalk length was an auxiliary trait, which could be used to guide T. yarkandensi breeding.

Abstract:Phosphoenolpyruvate carboxylase is a key enzyme in the gluconeogenesis pathway. When animals and plants are under adverse environmental conditions such as temperature stress, they can convert oxaloacetic acid into phosphoenolpyruvate, generating glucose to maintain the blood glucose balance. This process plays an important role in stress resistance. In this study, PEPCK gene of Pinctada fucata martensii was identified, the changes of PmPEPCK expression under low temperature stress were analyzed, and single-nucleotide polymorphism (SNP) sites in the exon region of PmPEPCK in low temperature tolerant breeding line F3 (R) and Beibu Gulf wild populations (W) of Pinctada fucata martensii were screened and compared. Sequence analysis showed that the PmPEPCK gene had a full length of 2557 bp; the 5?UTR and 3?UTR were 56 bp and 446 bp long, respectively, and the open reading frame was 2055 bp long and encoded 684 amino acids. PmPEPCK was expressed in the tested tissues, among which the hepatopancreas had the highest expression (P＜0.05). The time-series expression results in gill tissues after low temperature stress showed that the expression of PmPEPCK in the low temperature group reached the highest at 12 ℃ and 17 ℃ at 6 h, which was significantly higher than that at 22 ℃ noted in the control group (P＜0.05), indicating that PmPEPCK participates in the low temperature response process of shellfish. A total of 108 SNPs were identified in the exon region of PmPEPCK, of which 47 SNPs showed significant differences between the R and W population (P＜0.05). Among the 47 SNP loci, 11 genotypes only appeared in R, which were the AG genotype of loci g.60010420, g.60007411, and g.60011365; genotype AA of loci g.60006265 and g.60006166; genotype CT of loci g.60007389 and g.60011387; genotype TT of loci g.60009449 and g.60006028; genotype GG of locus g.60011341; and genotype GT of locus g.60009464. Thus, after 3 generations of selection, the PmPEPCK gene of the R population was strongly positively selected. These SNPs and their genotypes of PmPEPCK may be related to the low temperature tolerance of the breeding line and used as candidate markers for selective breeding.

Abstract:Artemia is an important live feed in shrimp larviculture. In this study, Artemia nauplii hatched from commercial Artemia cyst products originating from the Great Salt Lake in the USA, Aibi Lake in Xinjiang, China, Shuanghu Lake in Tibet, China, and Bohai Bay salt ponds in China were fed to Litopenaeus vannamei postlarvae (PLs) to evaluate the effects of Artemia feeding on growth, muscle composition, and resistance to ammonia nitrogen and salinity stress on the shrimps. L. vannamei PL5 were randomly divided into four groups. Each group contained three replicate tanks in which 1000 PLs were stocked at a density of 50 PLs/L. The PLs were fed newly hatched Artemia nauplii from different origins. The initial feeding ratio was 100 Artemia/(PL·d), which increased by 10% per day during the 15-day culture period. The results showed a significant difference in biometrics and nutritional composition of Artemia cysts and nauplii from different origins. Those from Shuanghu had the largest cyst diameter, Instar I nauplii length, individual dry weight, and the greatest crude protein and crude fat content. Additionally, they had the greatest arachidonic acid (ARA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) content in shrimp muscles. Although feeding Artemia nauplii from different origins did not result in a significant difference in survival rates, body length, muscle crude protein, or crude fat content of the PLs (P＞0.05), significantly higher ARA, EPA, and DHA content was observed in the muscles of shrimp that were fed with Shuanghu Artemia nauplii (P＜0.05). Furthermore, the highest total superoxide dismutase (T-SOD) activity was obtained in the hepatopancreas of shrimp that were fed with Shuanghu Artemia nauplii, whereas the highest acid phosphatase (ACP) activity was observed when feeding Aibi Artemia (P＜0.05). There was no significant difference in alkaline phosphatase activity among the groups (P＞0.05). Moreover, the shrimps that were fed with Shuanghu and Aibi Artemia had better resistance to high salinity and ammonia nitrogen stress, which may be related to the higher DHA and EPA content and higher T-SOD and ACP levels in the shrimps. The outcome of this study provided evidence for the effective application of Artemia with different origins in L. vannamei larviculture.

Abstract:Spawning grounds play a key role in recruiting fishery resources, and their health status directly contributes to the biomass dynamics and sustainability of fishery resources. In the present study, using spawning grounds in Shandong inshore waters as an example, based on the comprehensive analysis of various marine ecosystem health assessment studies, a health assessment system of the spawning ground was established by the analytic hierarchy process, and the evaluation results of the system were verified. Two first-level indicators were considered in the health assessment system, the environment and function of the spawning ground. Six second-level indicators were covered, namely, biotic environment, hydrological environment; human disturbance; fish eggs, larvae, and juveniles; spawning stock size; and spawning ground area. There were 21 third-level indicators. The health status of the spawning ground was characterized by a comprehensive health indicator (CHI), with the health status of the spawning grounds in Shandong inshore waters during the 1980s regarded as the baseline. The results of the health assessment system of the spawning ground conducted in this study were verified using the spawning ground health status in the Shandong inshore in May 2008 as an example. The average CHI was 0.571 in the spawning grounds in Shandong inshore waters during May 2008. In general, the spawning ground had a sub-health status. The CHI of the northern Shandong Peninsula, northern Haizhou Bay, southern Shandong Peninsula, and Laizhou Bay were 0.596, 0.593, 0.590, and 0.505, respectively. The accuracy of the evaluation system was proven by a comprehensive analysis of the results of related studies.

Abstract:A survey of early fish resources in the Fujin section of the lower Songhua River was carried out to know about the status of early fish resources and the location of spawning grounds from June to July in 2016—2018. A total of 8916 eggs and 31232 larvae were collected. A total of 33 species belonging to 7 families and 3 orders were identified by morphological and molecular biological methods. Among them, 12 fish species produced drifting eggs and floating eggs. The estimated abundance of fish eggs flowed through the Fujin section was 85.58×10⁸ eggs, 57.43×10⁸ eggs and 60.51×10⁸ eggs from 2016 to 2018, respectively. The dominant species were Hemiculter bleekeri bleekeri, Gobiobotia pappenheim and Saurogobio dabryi, and the abundance of fish eggs was 143.35×10⁸ eggs, 15.62×10⁸ eggs and 7.19×10⁸ eggs during the surveys, respectively. The spawning amount of these three dominant fishes accounted for 64.56% of the total spawning amount. The abundance of fish eggs of drifting egg fishes Hypophthalmichthys molitrix and Culter alburnus, and floating egg fishes Elopichthys bambusa and Siniperca chuatsi was 1.36×10⁸ eggs, 3.19×10⁸ eggs, 2.77×10⁸ eggs and 0.32×10⁸ eggs, respectively. According to the analysis of the developmental period and flow rate, the spawning grounds of Hypophthalmichthys molitrix originated from the Dulu River estuary to the Dailiangzi River in Huachuan County and from Suwopeng to the Zhonghe Village section. Redundancy analysis results showed that the drifting density of Hemiculter bleekeri bleekeri eggs was significantly correlated with transparency and that of Hypophthalmichthys molitrix, Culter alburnus, and Elopichthys bambusa was significantly correlated with water temperature and flow. In order to more effectively protect the fish resources of the lower Songhua River, it was recommended to increase the releasing number of fishes such as Ctenopharpharyngodon idellus, Mylopharyngodon piceus (Richardscn), Megalobrama skolkoui (Dybowski) and Culter mongolicus mongolicus (Basilewsky); establish a comprehensive prevention and control system for soil erosion in the Songhua River Basin to reduce the impact of soil erosion and water pollution on fish habitats; develop aquatic biodiversity observation, early warning, and evaluation systems to monitor key areas and key populations. Based on the scientific research and judgment of the monitoring results, we should adjust and optimize the Songhua River aquatic life protection measures.

Abstract:Coral reef ecosystems harbor the highest biodiversity of all marine ecosystems and are known as the “tropical rainforests in the ocean.” Fish biodiversity in coral reef ecosystems is extremely rich, as high as 1/3 of the total number of marine fishes. Importantly, reef ?shes are the major source of protein for many island nations and account for approximately 10% of the global ?sheries catch. Fish are an important part of coral reefs and an essential part of maintaining the health of coral reefs. Coral reef ecosystems provide habitat and the primary food sources for coral reef fishes. At present, the coral reef ecosystem off the coast of the South China Sea is experiencing a significant decline, fishery resources are under a serious threat, and catches have decreased significantly. To better understand and protect the coral reef ecosystem and fishes in the Qilian reef of Xisha Islands, we conducted comprehensive surveys from 2018 to 2020. Historical data showed that 315 fish species were found in Qilianyu Island, belonging to 49 families and 12 orders. Perciformes was the largest, accounting for 79.05%. A large number of fish species in Indo-Pacific coral reefs were composed of 29 families. In our survey, except for Microdesmidae, which was not found in this study, other 28 families were recorded and accounted for 89.52% of the total number of species. The results supported the classic theory of the high connectivity of coral reef fish. The cluster analysis of fishes on the reefs of the South China Sea at the family level showed that the coral reef fishes of Qilianyu were the most similar to the fishes of the three offshore reef islands in Vietnam. Overall, small fishes were the most abundant, accounting for 49.04%, followed by medium-sized fishes with 31.09%, and large-sized fishes with only 19.87%. Regarding food types, carnivorous fish were the most abundant with 163 species, followed by omnivorous fish with 91 species and herbivorous fish were the least with 61 species. A total of 37 fish species, mostly carnivorous species, were not found in recent years compared with the historical research data. Furthermore, large fishes were all carnivorous, indicating that the Qilianyu coral reef fishes are being overfished. The number of small fishes was as high as 66.57%, and most of these fish belonged to Pomacentridae, Chaetodontidae, and Labridae, which were all highly dependent on coral reefs, indicating a significant decline in the Qilianyu coral reef ecosystem. According to the number of coral species, it can be inferred that the number of fish species in the Qilianyu coral reef area would be 400 or more, indicating a rich fish diversity. However, nearly 100 species were not recorded in recent surveys, further indicating that the coral reef ecosystem has been severely disturbed by human and has declined. At present, the coral reef ecosystem of Qilianyu has been greatly affected by human activities, especially overfishing, which has led to an instability of the coral reef ecosystem. Therefore, protecting Qilianyu coral reef fish resources requires the control of fishing intensity and protection of this unique coral reef habitat.

Abstract:In this study, we analyzed the stomach contents of main fishes collected using a bottom trawling net in the offshore waters of southern Zhejiang, China from 2016 to 2019. By combining with the data of early feeding habits, we constructed the food web topology of the fish community based on interspecific trophic relationships. The keystone species of the fish community was determined using the topological network index and KPP calculation. The results showed that there were 276 pairs of trophic links in the food web based on the feeding analysis. Trichiurus lepturus with the highest D, D_in, CC, BC, and IC and Benthosema pterotum with the highest D_out, TI¹ , and TI⁹ had the highest rank among the 34 species, indicating that they were closely related to other species in the fish community and could control the stability of community structure and information diffusion. The key index of T. lepturus (K and K_t) and B. pterotum (K_b) had the highest value, indicating that they played a decisive role in the energy flow and information transfer of community structure. It was verified using KPP calculation that T. lepturus played a decisive role in the stability of fish community structure and the transmission of interspecific information in the offshore waters of southern Zhejiang. In this study, the keystone species of the fish community were identified using 11 topological parameters combined with KPP calculation. It was found that T. lepturus (D, D_in, CC, BC, IC, K, and K_t) and B. pterotum (D_out, TI¹ , TI⁹ , and K_b) played a key role in the stability of community structure, in which T. lepturus was the keystone predator and B. pterotum was the keystone prey.

Abstract:The fishway of the Xiajiang Hydro-Junction was built to meet the needs of breeding and over-wintering migratory fish. To alleviate the effects of its operation, netting and interception methods were used to conduct surveys to determine the effects of the fish passage at the Xiajiang Hydro-Junction during October 2019, January 2020, April 2020, and August 2020. A total of 4605 fishes was collected, including 42 species belonging to 4 orders, 9 families, and 34 genera, mainly small- and medium-sized fishes. The body length ranged from 2.3 cm to 48.5 cm. The dominant species were Zacco platypus, Squalidus argentatus, Saurogobio dabryi, Culter alburnus, and Pelteobagrus fulvidraco, accounting for 17.24%, 14.26%, 6.86%, 5.78%, and 4.89%, respectively. The migratory fishes in the fishway included Ctenopharyngodon idella, Squaliobarbus curriculus, Pseudobrama simoni, and Anguilla japonica. The number of passing fish varied seasonally and was the highest during summer, accounting for 42.23% of the total, whereas the number was the lowest during winter, accounting for 11.69% of the total. Factors affecting fish passing were mainly water temperature and water level. There were 42 species of fish passing through the entrance of the fishway of the Xiajiang Hydro-Junction. There were more species of fishes passing through the fishway of the Xiajiang Hydro-Junction than those through other fishways. These results will provide reference data for the optimization and effective operation of fishways, which could have implications in the protection of fishery resources in the Ganjiang River.

Abstract:为评估镇江长江豚类省级自然保护区鱼类资源密度及时空特征, 于 2018年在该水域进行了 4次水声学调查。 结果显示, 水声学调查所得鱼类资源密度均值范围为 0.090~0.575 尾/m² , 均值为 0.286 尾/m² ; 鱼类资源密度的空间分布特征随季节变化较明显, 7 月和 10 月, 和畅洲的南、北汊鱼类资源密度要显著高于其上游和下游; 1 月和 4 月, 则是和畅洲上、下游的资源密度相对较大, 其中 7 月保护区水域的鱼类资源密度最大, 1 月最小。调查水域内单体目标强度呈单峰状分布, 主要集中于?59.5~?53.5 dB, 春季、秋季和冬季的单体目标均匀分布于水深 10~40 m 的水层, 夏季则多集中分布于水深 5~20 m 的水层。本次调查较准确地反映了镇江保护区水域内的鱼类资源密度及其时空分布信息, 为保护区管理部门评价长江豚类的栖息地质量以及实施科学管护提供科学依据。

Abstract:Studying the ecology of fish parasite population is useful to understand the distribution characteristics of all individuals of the same population in a certain time and space, in addition to the growth and decline of the parasite population. In addition, it is important to study the relationship among parasite, host, and environment. There are many rivers and lakes in Tibet with a unique fish composition. However, little attention has been paid to the parasites of the indigenous fish in Tibet, and the research on the population ecology is very limited. Only the native fish in Lhasa River and Lake Chugutso and Glyptosternum maculatum in the Yarlung Zangbo River have been reported. Yamdrok Lake is located in the south of Tibet, and it is the largest lakes in the south of the Yarlung Zangbo River and the north of the Himalayas. Gymnocypris waddellii is the only Schizothorax fish in this lake with no known studies on its parasites. In this study, we evaluated the status of intestinal helminths of G. waddellii in Yamdrok Lake to further understand the fauna composition and characteristics of parasites of native fishes in Tibet. Our study may contribute to further research about fish, parasites, plateau uplift, and special geographical environments. We dissected 180 G. waddellii individuals in July 2020, identified and counted the parasitic helminths, and analyzed their spatial dynamics and distribution patterns. We found five intestinal helminths spe-cies: Parabreviscolex niepini, Contracaecum eudyptulae, Streptocara sp., Neoechinorhynchus sp., and Al-locreadium sp. The prevalence of Neoechinorhynchus sp. was the highest; the infection intensity and mean abun-dance of P. niepini was the highest; and the prevalence, infection intensity, and mean abundance of Streptocara sp. were the lowest. Moreover, t-test of independent samples showed that there was no significant difference in the mean abundance of male and female populations infected with intestinal helminths. The results of correlation analysis showed that there was no significant correlation between the total length of the host and the number of intestinal helminths. Distribution patterns of the five populations were analyzed by variance mean ratio, and the results showed that they were aggregated. The host frequencies in each population were fitted with a negative bi-nomial distribution, and the significance of the results was analyzed using x² -test. Although the populations of P. niepini and Streptocara sp. were aggregated, they did not conform to the negative binomial distribution. Among the five populations, the uninfected hosts had the highest frequency. In case of infection, the host frequency of P. niepini infected with 1–5 was the highest, C. eudyptulae and Allocreadium sp. infected with 1 was the highest, Neoechinorhynchus sp. infected with 1–2 was the highest, and the host frequency of Streptocara sp. was lower and similar when the number of infections was 1–6.

Abstract:Understanding the settlement process of longline gear is of considerable significance for increasing the catch rate of target species and reducing the bycatch of other species. In this study, based on the finite element theory, a three-dimensional dynamic settlement process model of longline settlement was constructed using the lumped-mass method. The wind speed and direction, three-dimensional current data, fishing gear parameters, and operational parameters of 12 sites measured at sea from March 2016 to July 2016 were used as inputs, and the seven level and six order Runge-Kutta method was used to solve the model. The depth and sinking duration of 80 hooks corresponding to the measured sites were calculated and the simulated sinking speed and gear spatial shape were obtained. These data were then compared with the measured data at sea. The results showed that: (1) the established three-dimensional settlement model of longline settlement could be used to calculate the hook depth, sinking duration, sinking speed, and gear spatial shape at the flow velocity in the X, Y, and Z directions of –0.05– 0.80 m/s, –0.30–0.28 m/s, and –0.12–0.10 m/s, respectively; (2) there were no significant differences among the hook depth, sinking duration, and sinking speed obtained using the three-dimensional settlement model and conventionally measured (P＞0.05); (3) the simulated gear space shapes were similar to those of the measured space shapes. The numerical simulation model developed in this study can predict the hook depth, sinking duration, sinking speed, and spatial shape under the interaction of three-dimensional ocean currents and achieve dynamic three-dimensional visualization.