Abstract:We developed a black shell color line (BF) based on the color of radiating ribbed stripes in shell prismatic layers and growth characteristics by employing family selection and population selection methods. We aimed to explore the production performance of the selected lines by comparing the performance indicators of the black shell color line F5 (BF5) and the control group (CG), including fertilization rate, hatching rate, metamorphosis rate, growth traits, tolerance to low temperature and high salt content, and pearl production traits. The fertilization, hatching, and survival rates on the 10th and 20th day of larvae and the metamorphosis rate of the BF5 population were higher than those of the CG population, but the difference was not significant (P＞0.05). Following 20 days post hatching, the average shell length of BF5 group was significantly higher than that of the CG group (P＜0.05), and the average shell length of the BF5 group was 17.47%, 21.34%, and 20.28% higher than that of CG group at 240, 330, and 600 days after hatching, respectively. Following 30 days of exposure to the heat stress caused at 33 ℃, the survival rate of BF5 and CG groups was 84.4% and 63.9%, respectively, and this difference was significant (P＜0.05). Following 30 days of exposure to 16‰ low salt stress, the survival rate of BF5 and CG groups was 69.2% and 56.7%, respectively, with significant differences being observed between the two groups (P＜0.05). From 150 days after nuclear implantation to the end of the beading period (270 days), the survival rate of BF5 was significantly higher than that of the CG population (P＜0.05). The survival rate of BF5 was 18.92% higher than that of CG. There was no significant difference between the commercial bead rate and the high-quality bead rate of BF5 and CG (P＞0.05). The nucleation retention rate and nacre thickness of BF5 were significantly higher than CG (P＜0.05), and the increase rates were 18.97% and 22.61%, respectively. Our results indicated that BF5 had better pearl production traits. The findings of this study provide basic data for breeding and industrial application of Pinctada fucata martensii.

Abstract:Darkbarbel catfish (Pelteobagrus vachelli) is native to the Yangtze River basin. This fish species is intensively cultured because of its economic value and genetic advantage in breeding. The development of a sperm cryopreservation technique has facilitated the reproductive management and conservation of germplasm resources of numerous aquatic animals. However, this technique has not been thoroughly studied and established in darkbarbel catfish. This study aims to assess the effects of different extenders, cryoprotectants, and freezing procedures on the sperm quality of darkbarbel catfish, to develop a cryopreservation protocol for this fish. Computer-assisted sperm analyses of darkbarbel catfish sperm motility and velocity revealed the preferable viability of semen in extender 2 (all g/L; NaCl 10.01, KCl 0.5, NaHCO₃ 0.44, MgSO₄·7H₂O 0.25, Na₂HPO₄·12H₂O 0.09, KH₂PO₄ 0.07, glucose 0.99). The optimal dilution ratio was 1:10. The effects of methanol, glycols, 2-methoxyethanol, and dimethylsulfoxide (DMSO) on darkbarbel catfish sperm before and after cryopreservation were assessed. Sperm stored in an extender containing DMSO displayed significantly lower motility before freezing and poor quality after cryopreservation (P＜0.05). Sperm motility and progressive motility were highest when methanol was used as the cryoprotectant. Sperm quality decreased significantly with increasing methanol concentrations before milt samples were frozen, with opposite results evident in post-thaw samples (P＜0.05). The progressive motility of darkbarbel catfish sperm following cryopreservation was highest in 10% methanol and was stable with further increases in methanol concentration (P＜0.05). Freezing and thawing procedures were optimized in this study. Equilibration time had no significant effect on sperm post-thaw quality. However, significant effects of fumigation height and time on sperm progressive motility were observed (P＜0.05). Sperm progressive motility displayed a significantly high value at the height of 7 cm above the surface of liquid nitrogen and then decreased significantly with increasing fumigation height (P＜0.05). Sperm placed horizontally 7 cm above the liquid nitrogen surface for 10 min exhibited preferable post-thaw quality. Thawing temperature and time did not significantly affect sperm total motility, but significantly affected the progressive motility of darkbarbel catfish sperm. The highest post-thaw sperm quality was observed using a water bath at a higher temperature of 42 for 9 s. In conclusion, the high quality of darkbarbel catfish sperm, compared to fresh milt, is ℃ achieved by storing the milt in extender 2 at a dilution ratio of 1:10, adding 10% methanol as a cryoprotectant, equilibrating at 4 ℃ for 30 min, fumigating 7 cm above the liquid nitrogen surface for 10 min, and thawing sperm at 42 for 9 s.

Abstract:Elucidating the occurrence and persistence of spawning grounds is warranted to minimize the damage caused by human activities to fish. Fish eggs and larvae, which aggregate in high numbers in a limited area, can be particularly vulnerable to negative environmental impacts. The increasing pressure on the fishery resources in Zhejiang fishing grounds have led to a sharp decline in the resources and damaged the structure of fish communities. In 2017, the government established the Qixing Islands and other 9 spawning ground reserves to protect and repair the resources of the main economic fish species. The Qixing Islands are a group of outer reefs in the southernmost part of Zhejiang Province. Located at the intersection of Taiwan Warm Current, Zhejiang and Fujian coastal currents, and the Kuroshio Current, the waters around these islands provide suitable hydrographic environment and abundant food resources, making it an ideal spawning and nursery ground for many fish species. The fish eggs and larvae phase marks a crucial period in early fish life as it is a highly sensitive and vulnerable stage. Changes in its abundance can directly impact population recruitment. Therefore, understanding the community structure of fish eggs and larvae is of great significance for conserving and utilizing marine fish resources. Additionally, fish community structures respond to the changes in environmental factors in the waters where they are located. At present, limited research has been conducted on fish eggs and larvae in the Qixing Islands spawning ground reserve. This study aimed to explore the correlation between the species composition of fish eggs and larvae and their relationship with environmental factors in the spawning ground reserve of Qixing Islands. Samples were collected during six cruises conducted in 2018 (April, May, and November) and 2019 (April, May, and November) using a large plankton net. These samples were then analyzed to assess the species composition, spatio-temporal distribution, community structure, and their relationship with environmental factors of fish eggs and larvae in this area. A total of 1490 eggs and 278 larvae were collected, belonging to 9 orders, 26 families, and 60 species. The most prevalent species of eggs included Harpodon nehereus, Konosirus punctatus, whereas those of larvae included Engraulis japonicus and Stolephorus commersonnii. The spatio-temporal distribution of fish eggs and larvae exhibited a non-stationary characteristic, primarily in the eastern part of the surveyed area. Moreover, there was a higher density of fish eggs and larvae in 2019 than in 2018. Cluster analysis and nonmetric multidimensional scaling (NMDS) sorting results indicated a highly significant difference (P= 0.001) in the cluster composition of eggs and larvae, and the community structure was characterized by obvious regional division. Mantel test correlation analysis and redundancy analysis showed that environmental factors such as temperature, salinity, and dissolved oxygen were closely related to the distribution of fish eggs and larvae. The study indicates that in the early stages of establishing protected areas, there has been a positive impact on the replenishment and restoration of early-stage fish resources. However, the area is predominantly characterized by small-sized and low economic value fish. In light of existing measures for the recovery of fisheries resources, it is recommended to further strengthen the conservation efforts for economically important species and promote their rational development and utilization. Spawning peaked during spring, with the reserve being predominantly populated by warm-temperature or warm-water species of fish during both spring and autumn. Less significant and smaller species dominate over those considered more significant and larger within the community. The spatial distribution trend indicated that the eastern part of the surveyed sea area was closer to the closed area line, followed by coastal areas and central region. Eggs were mainly concentrated in the waters around the closed area line, and larvae were densely distributed in coastal waters. Temperature, salinity, and dissolved oxygen influenced the distribution of eggs and larvae. The community structure of eggs and larvae in the spawning ground reserve of Qixing Islands was in a state of dynamic change, and the establishment of the reserve played a positive role in restoring the early resources of fish. The reserve remains the spawning and nursery ground for most fish species. Consequently, resource protection must be strengthened and rational development and utilization of economically important fish species must be undertaken by building upon the existing restoration measures used for fisheries resources.

Abstract:In Qidong, Jiangsu Province, there used to be 440 km² of mudflats, which is a crucial habitat for benthic shellfish—a significant and unique marine resource. However, human activities such as mudflat reclamation and coastal construction have reduced the suitable habitat for shellfish and altered the local ecological factors. Conversely, shellfish proliferation and release activities have also been performed frequently, which have impacted the resources, biodiversity, and overall equilibrium of benthic shellfish ecosystems. Presently, the lack of understanding regarding the distribution and community structure of shellfish resources has hindered the effective management of shellfish and the protection of germplasm resources. Conversely, there have been frequent shellfish proliferation and release initiatives. Here, we aimed to systematically understand the biodiversity and resource status of benthic shellfish, explore the main environmental factors affecting the community structure, and provide basic data for the shellfish resources protection and habitat restoration. For this, we surveyed 8 sections of Qidong intertidal mudflats in the spring and autumn of 2019 and analyzed the species composition, diversity, density, dominant species, and distribution of shellfish. A total of 30 species of benthic shellfish were recorded during the spring and autumn surveys, including 14 species of gastropods and 16 species of bivalves. Across the elevation gradient of the intertidal zone, the average density of benthic shellfish exhibited the following trend: high tide zone＞medium tide zone＞low tide zone. The dominant species of benthic shellfish in intertidal mudflats were Mactra veneriformis, Dosinia laminata, Meretrix meretrix, Moerella iridescens, and Bullacta exarate. The results of non-metric multidimensional scaling showed that the benthic shellfish could be divided into three groups. The first group comprised three tidal zones of the Q1 section (Lvsi harbour) housing M. iridescent and R. philippinarum; the second group included the three tidal zones of Q8 section (Qixingsha) and several middle and low tidal zones of central sections, with D. laminata and B. exarate being the predominant species. The remaining central sections formed the third group, with M. meretrix and M. veneriformis as the characteristic species. Canonical correlation analysis showed that the densities of both M. meretrix and M. veneriformis were positively correlated with sand content and D50, while being negatively correlated with clay content. The density of M. iridescens was positively correlated with clay content, while being negatively correlated with sand content. D. laminate was negatively correlated with total organic carbon. A clear differentiation was observed in shellfish composition in Qidong intertidal mudflats, owing to the significant differences in salinity and bottom plasmid diameter. Our results suggest that the northern mudflats must be developed into protection areas for small shellfish resources (such as M. iridescens and R. philippinarum). In contrast, the central coastal mudflat is suitable for large bivalve shellfish (such as M. veneriformis and M. meretrix). Sandbars are not conducive to the development of shellfish since they are susceptible to various factors such as channel fluctuations, strong tides, typhoons, and storm surges.

Abstract:Chub mackerel (Scomber japonicus) is an important pelagic fishery resource in the East China and Yellow Seas. Being a poikilotherm, its body temperature is sensitive to environmental temperature, and climate warming-induced alterations in the marine ecosystem have negatively impacted the life history and population dynamics of poikilothermal fish such as the chub mackerel. Understanding the relationships that climate warming shares with the individual life history of chub mackerel and its population dynamics are crucial for the sustainable utilization and scientific management of its resources. In this study, we aimed to investigate the effects of climate warming on growth, reproduction, survival, and population status of chub mackerel in the East China and Yellow Seas. We constructed the dynamic energy budget integral projection model (DEB-IPM) using dynamic energy budget and integral projection models. The results show that: (1) climate warming will increase the growth rate of chub mackerel in the early stage (age＜220 d), decrease the maximum body weight of adults, increase absolute fecundity, and increase natural mortality. Consequently, chub mackerel individuals will allocate more assimilative energy to reproduction, thus limiting the growth and abundance of large individuals in chub mackerel populations and causing individuals to be smaller in size. (2) The population growth rate of chub mackerel showed a unimodal change with temperature, i.e., population growth rate increased and then decreased with increasing temperature. (3) The growth and reproduction of small and medium-sized chub mackerel individuals (200–600 g) during the early growth stages were responsible for disturbing their population dynamics. However, under the influence of climate warming, the contribution of growth and reproduction of chub mackerel to allocation of optimal energy for population growth would be altered. This change led to a decreasing body weight with increasing temperature, corresponding to the peak of the sensitivity contribution. Hence, it is more important to protect the early stages of chub mackerel. While acknowledging uncertainties in estimating and setting model parameters, the DEB-IPM can simulate the effects of climate warming on the life history characteristics of chub mackerel individuals as well as the changes in population dynamics. This model serves as a valuable theoretical and modeling tool that facilitates the scientific management of chub mackerel in the East China Sea and Yellow Sea under the conditions of climate warming.

Abstract:The elements in the hard tissues of organisms are important natural markers for reconstructing their life history and habitat. The present study aimed to explore the changes in the elements present inside the statolith core and edge of Argentine shortfin squid (Illex argentinus) by using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The element content was determined in the core and edge of statoliths, and the ratios of Sr, Ba, Mg, Mn to Ca were analyzed. Thereafter, mixed-effects models were used to analyze the relationship between these four elements and Ca ratios in the edge and core of statoliths. Ba/Ca values were found significant differences in the core of statoliths between female and male individuals, so did in the edge of statoliths. Significant differences were also observed in the Ba/Ca values of statolith core among different hatching months. Additionally, in male individuals, the Ba/Ca values in the statolith edge exhibited notable variations across different sampling months. The Sr/Ca values in the core of statoliths and the Ba/Ca values in the edge showed significant differences between different sampling latitudinal centroids. The Sr/Ca, Ba/Ca, and Mg/Ca values in the core of statoliths were significantly higher than the corresponding element ratios in the edge, while no significant difference was observed in the Mn/Ca values between the core and edge of statoliths. The results of the mixed-effects model showed that there was no relationship between the element ratios in the edge of statoliths and the corresponding element ratios in the core for females, whereas the Ba/Ca and Mn/Ca values in the edge of statoliths increased with the increasing Ba/Ca and Mn/Ca values in the core for males. These findings suggest notable variations in Sr, Ba, and Mg elements between the core and edge of I. argentinus statoliths. Additionally, they highlight sex-specific differences, specifically in the Ba element. This study provides a basis for further revealing the environmental selection adaptability and life history of I. argentinus and can provide data reference for mastering the species resource fluctuations.

Abstract:The sea area near Gouqi Island harbors expansive floating colonies of Sargassum horneri, whose specific source remains unidentified. Despite this, the distribution of S. horneri in the intertidal zone is limited. Hence, analyzing the growth changes of both intertidal zone and raft S. horneri is essential for understanding the origins of “gold tide.” Previous studies have demonstrated a correlation between the growth of intertidal zone and S. horneri and the changes in effective accumulated temperature. Furthermore, it is suggested that temperature and irradiance may have varying effects on the growth of intertidal zone and raft S. horneri. In this study, we aimed to explore the specific sources of floating S. horneri in the sea area near Gouqi Island. We also aimed at elucidating the growth patterns of both intertidal zone and raft S horneri and identifying the required effective accumulated temperature. Additionally, we aimed to discern the distinct impacts exerted by temperature and irradiance on these growth patterns. Intertidal zone and raft S. horneri were collected monthly between September 2022 and June 2023. The temperature and irradiance changes during the life cycle in this period were recorded, and the variations in different plant traits, such as plant height, wet weight, longest primary branch length, were analyzed. Lastly, the effects of temperature and irradiance on the growth of S. horneri were also investigated. The results are summarized below: Average plant height, wet weight, and longest primary branch length of raft S. horneri were (168.1±21.0) cm, (147.6±24.1) g, and (131.8±26.4) cm, respectively, which were much larger than those of intertidal zone S. horneri [(67.9±22.5) cm, (62.4±16.7) g, and (46.4±10.6) cm]. Before the breeding period, the growth rates of wet weight, plant height, and longest primary branch length of raft S. horneri were much higher than those of intertidal zone S. horneri. Raft S. horneri grew rapidly compared to intertidal zone S. horneri. The low temperature condition of about 9 ℃ limited the growth of S. horneri, and the stable irradiance around 35 μmol/(m² ·s) may be the key factor that leads to the effective accumulated temperature required for the growth of raft S. horneri. This value was much smaller than that of intertidal S. horneri. Additionally, the breeding time of raft S. horneri was 1–2 months earlier than that of intertidal zone S. horneri, and the growth rate of the former was much greater than that of intertidal zone S. horneri. Raft S. horneri may contribute significantly to the floating S. horneri population in the sea area near Gouqi Island. Our results illustrate that the growth rate of plant height, wet weight and longest primary branch length of the raft S. horneri was much faster than that of the intertida zone S. horneri, and it suggest that irradiance is the key environmental factor affecting the growth and reproduction of intertidal zone and raft S. horneri. These results provide a scientific evidence for identifying the source of floating S. horneri, which may assist its efficient cultivation in the sea area near Gouqi Island. In addition, the study confirmed the interference of external factors; for example, the impact of waves on the growth of intertidal zone S. horneri was much greater than that on the growth of subtidal zone S. horneri. Hence, the maximum plant height of intertidal zone S. horneri at similar temperatures and greater irradiance was smaller than that of subtidal zone S. horneri, and the decay was faster than subtidal zone S. horneri.

Abstract:The jumbo flying squid Dosidicus gigas, which is widely distributed in the eastern Pacific Ocean, has been regarded as an important fishing target for Chinese distant-water fisheries. Previous studies have linked the fluctuations in squid catch to varying local environmental conditions and climate shifts, such as sea surface temperature, chlorophyll-a, and El Niño-Southern Oscillation. As a short-lived cephalopod, D. gigas is sensitive to environmental changes caused by climatic events, leading to changes in both the spatial and temporal distribution of its habitats. The Pacific Decadal Oscillation (PDO) is a strong indicator reflecting climate and environmental changes occurring across interdecadal time scales within the Pacific region. Though the oscillation between the warm and cold phases of the PDO can affect the marine ecosystem and fishery industry in the Pacific Ocean, limited research has been conducted on its effect on short-lived cephalopod species, particularly D. gigas. In addition, D. gigas has a diurnal vertical migration pattern, which is influenced by water temperature. Studies have demonstrated that employing a habitat model that incorporates vertical water temperature factors leads to improved simulation and prediction of the distribution of D. gigas habitats. In this study, we aimed to analyze the long-term changes in the vertical water temperature and suitable habitat of D. gigas in different PDO periods. We calculated the suitability index (SI) of vertical water temperature and the habitat suitability index (HSI) of D. gigas from 1950 to 2015 off Peru using four key water temperature factors at 0, 50, 100, and 150 m. The water temperatures at all four depths in the Peruvian waters were significantly higher during the warm phase of the PDO than those during the cold PDO phase. The HSI observed on the fishing ground displayed a significant negative correlation with the PDO index. In the cold phase of the PDO, the vertical water temperature off Peru experienced cooling, leading to higher quality habitat for D. gigas. This shift caused the favorable water temperature range to move northwestward, inducing an increase in the habitat suitability. The suitable habitat expanded and shifted northwestward. However, during the warm phase of PDO, vertical water temperatures increased, which was unfavorable to the growth of D. gigas. Moreover, the suitable water temperatures range decreased, resulting in lower HSI and a southeastward shift of suitable habitat. In addition, there were significant seasonal variations in the suitable habitat of D. gigas. In contrast to spring, HSI exhibited higher levels during summer, which coincided with expansion of suitable habitat towards northeast. Our findings suggested that spatio-temporal distribution of D. gigas habitat is closely related to the changes in seawater temperature at different water layers driven by the PDO phase shift. Moreover, there are clear seasonal variations in the distribution of this habitat.

Abstract:Bioamines play important roles in organisms, including controlling the biosynthesis of nucleic acids and stabilizing their structure to prevent denaturation. However, excessive intake of bioamines within a short period can inhibit the detoxification system. Meanwhile, excessive bioamines can damage the human body, even proving fatal. Pelagic marine fish such as Scomber japonicus and Engraulis japonicus are rich in ornithine, histidine and other amino acids, and related proteins. However, these compounds are easily decomposed by endogenous and exogenous enzymes during the storage of fish, resulting in the rapid production of several biogenic amines. Hence, they are labelled as fish with high biogenic amines. Several pelagic marine fish resources—an indispensable and important fishery resource in China and even globally—are at risk of high biogenic amine content. Here, we aimed to investigate the variations in different indicators during the spoilage of high biogenic amine fish and identify appropriate storage methods for them. S. japonicus and E. japonicus, two important pelagic fishes and typical high biogenic amine fishes in the eastern coastal areas of China, were selected as research subjects. Different indicators were assessed during the spoilage process, including pH, biogenic amine content, and volatile gas. Logistic analysis of biogenic amine content and linear discriminant analysis of volatile gas were performed. We found that S. japonicus and E. japonicus should not be stored for more than 3 days in cold temperatures (4 ℃). When S. japonicus was stored for ＞ 18 h and E. japonicus for ＞ 12 h at room temperature (25 ℃), significant changes were observed in their flavor and safety. Freezing temperature is the suitable storage temperature for S.japonicus and E. japonicus. Generally, the content of histamine in fish with high biogenic amine is higher than that of other biogenic amines; however, our study revealed that the content and change rate of cadaverine are higher than that of histamine in E. japonicus during the spoilage process. Therefore, cadaverine may be used as an indicator of the spoilage stage of E. japonicus, and detecting cadaverine in certain fish might better reflect the extent of spoilage compared to solely measuring histamine content. The results of this study provide theoretical support for the evaluating quality changes and safety control of fish with high biogenic amine. Moreover, they play a crucial role in early warning aimed at preventing poisoning associated with high biogenic amine fish.

Abstract:Enterocytozoon hepatopenaei (EHP) is a microsporidian parasite that infects shrimp. Although EHP infection does not cause widespread mortality in shrimp, it significantly slows down their growth and makes them more susceptible to other pathogens, resulting in significant economic losses. Thus, it has emerged as a major threat to the shrimp farming industry. The successful decoding of its genome sequence and genetic code has provided a robust foundation for various fundamental research endeavors. These endeavors provide valuable data essential for the identification and exploration of important functional genes in EHP. Here, we aimed to study the basic information regarding microsatellites in the EHP genome and provide theoretical support for molecular marker development, population evolution, and genetic diversity studies of EHP and its related species. We used bioinformatics to analyze the quantity, distribution, and frequency of SSR (simple sequence repeat) sites in the whole EHP genome and compared them with the corresponding properties of five other microsporidian fungal species. A total of 794 SSRs were identified in the EHP genome, with a total length of 21773 bp, accounting for 0.72% of the genome. The average length of SSRs was 27.43 bp, with a relative abundance of 262 loci/Mb and a relative density of 7184.43 bp/Mb. Of the six identified types of SSRs, tetranucleotide SSRs were the most prevalent, with 570 SSRs and a total length of 12152 bp; they accounted for 71.79% of the total SSRs, the average length of SSRs was 21.32 bp, with a relative abundance of 188.08 loci/Mb and a relative density of 4009.79 bp/Mb. Dinucleotide SSRs were the least prevalent, with only 20 SSRs and a total length of 280 bp; they accounted for 2.52% of the total SSRs, the average length of SSRs was 14 bp, with a relative abundance of 6.6 loci/Mb and a relative density of 92.39 bp/Mb. The most frequently occurring SSR in the genome (≥10) included AACT, TTAG, TAGT, ACTA, AGTT, CTAA, AACTA, GTTA, TTAGT, TAAC, and AT. Thirty multi-nucleotide SSRs with sequence lengths≥20 bp were selected for primer design for species identification. The genes containing SSRs were functionally annotated using the Gene Ontology database, and a total of 28 genes (3.53%) were annotated into three categories: molecular function, biological process, and cellular component. Compared to other microsporidian fungi, EHP has a moderate abundance of SSRs, and the quantity of SSRs is independent of genome size. This study provides a theoretical foundation for population genetics and evolutionary research of EHP.