To address the quality divergence between wild and cage-farmed red sea bream (Pagrus major), we conducted a comparative analysis of their proximate composition, fatty acid and amino acid profiles, and chromatic characteristics across varying size and growth stages. Farmed fish exhibited substantial lipid deposition (peaking at 4.77% in F4), yielding a high relative percentage of n-3 long-chain polyunsaturated fatty acids. In contrast, wild fish maintained a leaner muscle profile (<2.43% lipid) and were uniquely characterized by an elevated abundance of C22:1n-9 (up to 11.52%), distinguishing them from farmed cohorts. Regarding sensory quality, large-sized wild specimens contained significantly higher concentrations of delicious amino acids (DAA, up to 8.83 g/100 g), particularly glycine and alanine, indicating a superior flavor profile. Colorimetric analysis demonstrated that wild fish maintained vivid reddish pigmentation in the caudal fin (a* = 8.73), whereas farmed fish exhibited marked skin darkening. These findings elucidate a distinct phenotypic and nutritional divergence: intensive farming enhances overall somatic lipid retention, while natural marine environments optimize flavor-active amino acid accumulation and visual appeal, providing critical baseline markers to guide precision aquaculture.

Bivalves possess a diverse array of photoreceptive organs that are significant for their evolutionary success and systematic classification. Giant clams are the largest bivalve mollusks, with mantle tissue permanently extended in nature to maintain symbiosis with zooxanthellae and perceive environmental cues. Eyes serve as critical sensory organs for these organisms, yet the structural and functional characteristics of tridacnine eyes remain inadequately understood. This study systematically investigated the ocular traits and visual resolution of three ecologically distinct giant clam species (Tridacna crocea, T. squamosa, T. maxima) using morphometric analysis, hematoxylin-eosin (HE) staining, transmission electron microscopy (TEM), and grating stimulation assays. Significant interspecific differences were observed in eye count, diameter, and pupil-to-eye ratio (PER): T. maxima exhibited the highest mean eye count (221 ± 8), T. squamosa the largest mean eye diameter (0.490 ± 0.082 mm), and T. crocea the highest mean PER (0.363 ± 0.041). Eyes were numerically symmetric on the left and right mantles but positionally asymmetric, showing random distribution patterns along the mantle margin without fixed corresponding locations across species. All three species possessed typical pinhole eyes lacking lenses and retinas, primarily composed of filler cells, receptor cells, and sparse neurons, with symbiotic zooxanthellae distributed in the surrounding mantle tissue. Grating stimulation assays revealed resolvable stripe periods of 5.82-11.64° (T. crocea), 8.62-13.16° (T. squamosa), and 10.15-12.26° (T. maxima), confirming T. crocea as the species with the highest visual resolution. These ocular variations are inferred to reflect adaptive evolution driven by ecological niches and habitat-specific factors (water depth or light intensity), while the simplified pinhole morphology is consistent with their sedentary lifestyle and metabolic dependence on symbiotic zooxanthellae. These ocular variations provide potential morphological markers for the systematic classification of Tridacninae and offer valuable insights for researchers studying the evolutionary plasticity of bivalve visual systems.

To address the need for accurate onchidiid slug species identification, the present study engineered a multiplex PCR-based assay to facilitate the efficient, economical, and discrimination of five morphologically similar onchidiid slug species endemic to the South China Sea: Onchidium stuxbergi, Peronia verruculata, Onchidium reevesii, Platevindex martensi and Paromoionchis tumidus. A diagnostic multiplex PCR assay was designed based on a partial fragment of the mitochondrial cytochrome oxidase subunit I. It utilizes a shared forward primer and five taxon-specific reverse primers to simultaneously produce amplicons of varying sizes, each indicative of a particular species. Five species of Onchidiidae can be identified in a single reaction, which provides technical support for molecular identification of Onchidiidae. The development of a simple, effective and rapid multiple PCR identification method is of great significance for stock management and germplasm conservation of Onchidiidae.

Metamorphosis, the crucial transition from planktonic to sessile life stages, marks a key developmental milestone in marine bivalves, particularly for commercially valuable species like Lutraria sieboldii. We conducted a comprehensive transcriptomic analysis using RNA sequencing (RNA-seq) during the larval settlement stage to elucidate the molecular mechanisms underlying this ecologically and economically significant process. Our study generated 89.64 Gb of high-quality clean data (≥6.20 Gb per sample, Q30 ≥ 92.7 %), ensuring robust and reliable insights into gene expression dynamics. Through weighted gene co-expression network analysis (WGCNA), we identified the turquoise module as a key regulatory network strongly associated with settlement-related traits. This module was significantly enriched in critical biological processes, including mRNA splicing via spliceosome, pathways related to cytoskeletal organization and calcium signaling, and C-type lectin receptor signaling, which are crucial for substrate interaction and tissue remodeling. Notably, hub genes within this module included essential components of the spliceosome (SF3B1, RBM8A), calcium signaling regulators (CALM3), and cytoskeletal modulators (ACTB, MFAP1). Furthermore, transcriptional profiling revealed a significant upregulation of genes involved in inorganic ion transport and metabolism, cytoskeletal dynamics, protein turnover, and energy production. These results offer strong evidence for the coordinated regulation of molecular mechanisms during substrate recognition and tissue restructuring in L. sieboldii metamorphosis. As the first comprehensive transcriptomic resource describing larval settlement in this species, our study advances our understanding of conserved developmental pathways and suggests potential aquaculture strategies, such as optimizing calcium signaling or spliceosome activity to enhance larval settlement efficiency in hatchery settings.

Saccostrea mordax is an ecologically important bivalve species and a potential genetic resource for oyster breeding that inhabit in the Indo-Western Pacific region, characterized by three distinct lineages: A, B, and C. However, limited information is available about its genetic variation and genetic structure. The present study was conducted to study genetic diversity and population structure of S. mordax lineages A, B, and C based on mitochondrial COI gene data across the South China Sea and Celebes Sea. The UPGMA phylogenetic tree among populations, BI phylogenetic tree among individuals and median network revealed three main clusters, corresponding to S. mordax lineages A, B, and C. The results of K2P sequence divergence, pairwise Φst, gene flow and AMOVA indicated clear genetic differences among the lineages, combined with sympatric in all 7 geographical populations, these suggests lineages A and B are transitional periods of new species formation. Moreover, different patterns of population subdivision were found within lineages A, B and C. In lineage A, significant genetic differentiation was only observed between YM (Celebes Sea) and other populations (South China Sea), with a significant correlation between geographical distance and genetic distance among populations. In lineages B and C, there was no genetic differentiation between YM (Celebes Sea) and other populations (South China Sea), and no significant correlation between genetic distance and geographical distance among populations. The population history analyses indicated that populations of lineage A have experienced a recent sudden expansion, while populations of lineages B and C were large stable. These findings are essential for the conservation, sustainable utilization, and ecological restoration of S. mordax.

Global warming has significantly increased the frequency of marine heatwaves, causing severe and long-term impacts on tropical marine ecosystems and coral reef systems. As a key component of coral reefs, giant clams (Tridacna spp.) and their symbiotic algae are critical to ecosystem health, yet their complex regulatory mechanisms under environmental stress remain poorly understood. Our study revealed that while temperature fluctuations minimally affected the growth rates of giant clams, they significantly reduced survival probabilities. Physiological indicators demonstrated that giant clams mitigate oxidative stress caused by heatwaves through the regulation of antioxidant enzymes, such as catalase (CAT), glutathione reductase (GSH), and acid phosphatase (ACP), which play a key role in immune regulation and stress mitigation. For symbionts, with the elastic change of biomass, photosynthetic efficiency and chlorophyll content show dynamic changes, which is consistent with the pattern of symbionts' loss or death. Transcriptomic analysis further revealed distinct regulatory pathways for both giant clams and zooxanthellae under heatwave conditions, including nutrient metabolism, transport, energy distribution, and immunomodulatory responses. Notably, lipid metabolism genes were down regulated in host cells, suggesting reduced metabolic activity, while the MAPK (Mitogen-Activated Protein Kinase pathway) pathway was highly activated in clams, indicating enhanced immune responses to temperature stress. Conversely, the ABC (ATP-binding cassette transporter) transporters were significantly upregulated zooxanthellae, likely facilitating stress-related material transport. These findings highlight the need for integrated strategies targeting transcriptomic adjustments across symbiotic partners under stress-specific conditions, offering valuable insights into enhancing Tridacna resilience and addressing the broader impacts of climate change on marine ecosystems.

Typhoon climates and extreme rainy seasons drive changes in seawater salinity and quality, threatening coral reef ecosystems. As key contributors to coral reef ecosystems, giant clams face major survival pressures from salinity fluctuations. Understanding their salinity adaptation and recovery strategies is thus critical for the long-term conservation and sustainable management of coral reefs. Here, we integrated physiological and meta-transcriptomic analyses to investigate responses of Tridacna crocea to hypo-saline conditions (20 ppt, 27 ppt) and subsequent recovery at 34 ppt. Hypo-salinity significantly reduced growth and survival, with only 69 % survival at 20 ppt, while elevated sodium-potassium pump (NKA) activity was observed, facilitating ion balance maintenance. Meta-transcriptomic analysis revealed downregulated genes related to antioxidants (GGT1), ABC transporters (ABCB11, ABCA12), and fatty acid metabolism (ACAA1), alongside upregulated genes involved in amino acid metabolism (AGXT2, ALDH4A1). Symbionts exhibited decreased photosystem II (PSII) activity, reactive oxygen species (ROS) accumulation, and expulsion. Notably, partial recovery was achieved under 27 ppt hypo-salinity, whereas 20 ppt induced irreversible damage. Collectively, T. crocea copes with hypo-saline stress through coordinated regulation of ion transport, amino acid metabolism, and symbiont functionality, with 27 ppt potentially emerging as a critical threshold for recoverable adaptation. These findings provide valuable mechanistic insights to inform coral reef conservation strategies under global climate change.

The economic success of marine aquaculture for commercially significant species like Pagrus major hinges on predictable production cycles and efficient management. However, the growth dynamics of P. major in net-cage culture conditions are complex, shaped by fluctuating environmental variables and intensive management inputs, making accurate prediction of its growth trajectory a persistent industry challenge. Therefore, developing a robust and reliable growth model is a critical necessity for the sustainable development of the P. major industry. To address this practical need, a one-year growth monitoring study was conducted. Three nonlinear growth models, Logistic, Gompertz, and Von Bertalanffy, were fitted to the body weight data. The goodness-of-fit of these models was evaluated based on statistics such as the coefficient of determination (R2), Akaike information criterion (AIC), and Bayesian information criterion (BIC). The results showed that among the three models, the Logistic model provided the best fit for the body weight of net-caged P. major (R2 = 0.980, lowest AIC and BIC values). Based on this model, the predicted asymptotic body weight (A) was 370.7 g. The age at the inflection point (Ti) was 11.6 months, with a corresponding body weight at the inflection point (Wi) of 185.3 g, and the maximum monthly weight gain (Mg) was 43.9 g. The growth of P. major followed a sigmoid curve and exhibited distinct phasic characteristics: a relatively slow initial growth, a subsequent rapid growth period, and a decelerated growth rate in the later stage. These growth phase transitions coincided temporally with the dynamic changes in water temperature and salinity. This study provides a scientific basis and a practical model for the precision management, determination of optimal harvest size and timing, and evaluation of the economic efficiency of P. major aquaculture.

Being a major pathogen affecting the health of largemouth bass (Micropterus salmoides) aquaculture, Micropterus salmoides rhabdovirus (MSRV) causes significant economic losses. Galla chinensis, a traditional Chinese medicinal herb, possesses diverse biological activities, including antiviral properties. This study evaluated the role of Galla chinensis in MSRV infection in vitro and investigated its mechanism of action. Specifically, we examined the effects of Galla chinensis on MSRV virions, the MSRV infection process (adsorption, invasion, and replication), and the host immune response. The results demonstrated that Galla chinensis exerted grateful antiviral effects against MSRV in vitro. It inhibited MSRV infection by interacting with MSRV particles and interfering with the adsorption, invasion, and replication stages of the infection cycle. Furthermore, Galla chinensis up-regulated the expression of antioxidant genes (GSH, and CAT), enhanced the activity of SOD, and limited the production of ROS, down-regulated pro-inflammatory cytokine expression (TNF-α, IL-8, and IL-1β), and suppressed MSRV-induced cell apoptosis, collectively contributing to its antiviral efficacy. These results suggested that Galla chinensis was a promising anti-MSRV candidate with a distinct antiviral mechanism, providing a theoretical basis for developing MSRV prevention and control strategies.

Pagrus major is a marine fish of significant economic importance in aquaculture, where improving growth traits through selective breeding is a primary goal. To provide a scientific basis for such breeding programs, this study investigated the morphological growth patterns of red sea bream under cage culture at different developmental stages and identified key morphological indicators influencing body weight. The study measured body weight and 16 phenotypic traits in 500 red sea bream individuals at five age points (3, 6, 9, 12, and 15 months). Correlation analysis, path analysis, and stepwise multiple regression methods were used to elucidate the direct and indirect effects of various morphological traits on body weight. The results revealed that key morphological traits influencing body weight, such as body length and body depth, varied significantly with age. During the early growth stage (3, 6 months) and at 12 months of age, body length was the primary influencing factor (path coefficients of 0.522, 0.407, and 0.452, respectively). However, at 9 and 15 months, body depth became the dominant factor. Notably, at 15 months of age, tail fin length exhibited a significant negative direct effect on body weight. The multiple regression models established for all ages were highly significant (P < 0.01), with coefficients of determination all exceeding 0.850. The results indicate that red sea bream exhibits an allometric growth strategy, characterized by a transition from early body length growth to later body depth growth. To maximize breeding efficiency, we recommend a staged indirect selection strategy: using body length as the primary selection criterion for individuals under 1 year of age and body depth as the core criterion in later stages. This study provides a theoretical foundation for scientifically staged breeding of red sea bream.

A newly discovered oyster species, Crassostrea dianbaiensis, has been found in southern China, exhibiting traits of fast growth, high salt resistance, and drought resistance. C. iredalei is the main commercial species in Southeast Asia, favored by consumers for its delicious flesh and large size. These two oyster species share overlapping ecological niches and have a close genetic relationship. To explore the potential for interspecific hybridization between the two species and assess the growth and survival of their offspring, a 2 x 2 reciprocal cross experiment was conducted. The results showed clear asymmetry in fertilization success between C. iredalei female x C. dianbaiensis male (ID) and C. dianbaiensis female x C. iredalei male (DI). The fertilization and cleavage rates of DI were not significantly different from C. dianbaiensis female x C. dianbaiensis male (DD) (P > 0.05), but were significantly higher than those of C. iredalei female x C. iredalei male (II) and ID (P < 0.05). The survival rate of DI larvae was significantly higher compared to the other groups. Over 50% of DI larvae developed eyespots and began attaching by the 12th day, while ID larvae exhibited slow growth, with a survival rate of just 0.73 +/- 0.32% on the 15th day. Notably, very few ID larvae developed eyespots and began attaching by the 21st day, and all died during the metamorphic stage. On the 360th day, the shell heights of the 3 oyster groups in the Sanbaimen sea followed the order of DI > DD > II, while in Oushi's pond, the order was DD > DI > II (P < 0.05). The survival rates of DI and DD were significantly higher than II in both locations, with DI showed significantly higher total weight and relative yield than the others (P < 0.05). Moreover, DI produced normal gametes in terms of morphology and closely resembled DD in shell shape and texture. However, the flesh color and inner shell color of DI were more similar to C. iredalei. Therefore, DI is suitable for widespread cultivation in marine areas of Southern China, enriching the genetic resources of oyster in the subtropical sea zone.

Interspecific hybridization of oysters is a highly efficient breeding strategy that can produce commercially viable phenotypes. Crassostrea hongkongensis, the primary cultivar in southern China, faces increasing summer mortality risks and slow growth rates, which elevate commercial risks for farmers. C. iredalei, a commercially cultivated species in Southeast Asia, has been expanding its ecological niche northward in recent years, providing opportunities for interspecific hybridization with C. hongkongensis. This study conducted a 2 x 2 factorial cross between C. hongkongensis and C. iredalei (II: C. iredalei female x C. iredalei male, HH: C. hongkongensis female x C. hongkongensis male; IH: C. iredalei female x C. hongkongensis male, HI: C. hongkongensis female x C. iredalei male) and set up 6 salinity treatments (14, 17, 20, 23, 26 and 29 ppt) to explore the optimal salinity for embryo hatching. The results showed that the hybridization was successful, despite bidirectional fertilization and pronounced asymmetry in fertilization success. The optimal hatching salinity for C. iredalei and C. hongkongensis was 23 ppt and 17-20 ppt, respectively, while the optimal salinity for reciprocal hybrids was 20 ppt. Notably, the hatching rate of IH was lower than that of the control group at the optimal salinity. During the pelagic larval stage, hybrid larvae exhibited significant hybrid inferiority, with slower growth rates and higher mortality rates compared to intraspecific hybridization. It is worth noting that IH failed to overcome genetic incompatibility, resulting in complete mortality during the pelagic larval stage and failure to enter the growth stage. At the 360th day of the growth period, HI hybrids grown in Sanbaimen Sea exhibited significant hybrid vigor in shell height (15.65 %), and in Daya Bay Marine Biology Research Station, Chinese Academy of Sciences (MBRS), they showed significant single-parent hybrid advantages in shell height (28.44 %) and cumulative survival rate (58.11 %) compared to C. hongkongensis. In terms of gonadal development, HI hybrids were able to produce functional and viable gametes, although with some delay compared to their parents. The hybrid offspring inherited the phenotypic traits of their parents, with a grayish-yellow flesh color intermediate between the two oyster species. HI is a valuable genetic resource for oyster breeding, and its growth potential should be further explored to meet commercialization demands.

Crassostrea dianbaiensis, a recently identified species with significant commercial potential, has been successfully hybridized with Crassostrea iredalei, demonstrating that fertilization can be bidirectional. Notably, only the DI hybrid lineage (C. dianbaiensis♀ × C. iredalei♂) achieves maturity. These DI hybrids display remarkable growth vigor and survival advantages over their parental strains. To further investigate the trait segregation patterns in the F2 generation and the stable inheritance of heterosis, an intraspecific-crossing experiment was conducted with mature DI individuals, and place the juvenile shellfish in natural sea areas and artificial ponds for comparative aquaculture. The study involved crossing within C. dianbaiensis, C. iredalei, and mature DI individuals. The results indicated that F2 hybrids could fertilize successfully and develop normally, but exhibited signs of outbreeding depression during the planktonic larval stage compared to the grandparental species. Genetic analysis using ITS1 markers classified F2 individuals into three distinct categories: F2-I, F2-D, and F2-H. Water temperature fluctuations during the growth phase in Oushi’s ponds were more extreme than those observed in the Sanbaimen sea. On day 360, the ratio of F2-I, F2-D, and F2-H in Oushi’s ponds was approximately 1:1:4, contrasting with a 1:1:2 ratio in the Sanbaimen sea. This indicates that F2-H has a higher survival rate in Oushi’s ponds with drastic temperature changes. In addition, nearly all F2-D individuals showed phenotypic traits surpassing the F2 average. Histological examination of gonads indicated that all three F2 types were capable of gamete production, albeit with delayed gonadal development relative to age-matched grandparental species. In conclusion, both F2-H and F2-D exhibited heat tolerance and enhanced growth rates, respectively, suggesting their potential as new foundational breeding stocks for targeted development of strains adapted to large-scale aquaculture in southern China.

Argopecten irradians concentricus has become one of the pillar industries in the aquaculture of the Beibu Gulf since it was introduced into China in 1991. This study examined how stocking density and culture site affects growth in breeding populations, compared their growth performance and genetic diversity within control populations, and identified optimal culture locations for A. i. concentricus in the Beibu Gulf. The environmental investigation results revealed that among the three aquaculture sites of Beihai (BH), Qinzhou (QZ) and Fangchenggang (FCG), the fluctuation ranges of salinity, pH, and dissolved oxygen at the BH site were relatively narrower. The sum of all algal genus abundances of the three sites were 155,370 cells∙L−1, 931 cells∙L−1, and 47,957 cells∙L−1, respectively. Chaetoceros was the sole dominant algal genus in both BH and FCG, while Pleurosigma was the only dominant genus in QZ. The experimental results of growth demonstrated a significant negative correlation between growth rate and stocking density (p < 0.05). The mortalities of the QZ populations were significantly higher than those of the BH and FCG populations (p < 0.05). In comparison with the control populations, the breeding populations exhibited better growth performance but lower genetic diversity. FCG is a suitable location for cultivating the breeding population of A. i. concentricus. The findings of this study can serve as a reference for further understanding of the aquaculture strategy and genetic diversity of A. i. concentricus in the Beibu Gulf, China.

Interspecific hybridization represents a significant approach for developing enhanced economic traits in aquatic species, and it was established in oyster breeding. However, early research has still needed to further deepen the understanding of the mechanisms of oyster hybridization advantages. Prior research has indicated that Crassostrea iredalei and C. dianbaiensis, as locally unique varieties, are used to hybridize and obtain excellent performance progeny, and analytical hybrid advantages may be representative. In this study, hybrid oyster DI (C. dianbaiensis ♀ × C. iredalei ♂) and its parents were subjected to long-term in situ tracking (180-day-old, 270-day-old, and 360-day-old), and comprehensively evaluated the dynamic regulation of physiological indicators and molecular levels related to hybrid dominance. Our findings revealed that hybrid progeny showed excellent performance in both growth and survival rate. In addition, the survival level of the DI population under different salinity stress is higher than that of its parents, which once again proves that DI has excellent phenotypic characteristics of heterosis. Transcriptome results from both tissues also support the gene expression pattern of the offspring approaching maternal genes. This maternal effect shows similar functional classifications in both the adductor muscle and the mantle, mainly reflected in the proliferation, metabolism, and immune resistance of cells, implying that the hybrid advantage of hybrid progeny comes from the main effect of the maternal parent. Simultaneously, genes exhibiting a positive-dominant expression pattern, originating from parental effector genes, have also been identified. Interestingly, candidate genes (ADAMTS16, FUCA1, PI4KA, SLC7A9, TCF7L2, and CSNK2A2) are considered to be markers related to growth traits in other aquatic animals. Candidate genes associated with immunomodulatory signaling pathways and resistance (SMAD4, MYD88, BIRC3, BIRC7, and PPTC7) were also screened. Notably, genes related to salinity adaptive regulation (SLC23A2 and SLC12A1) were screened, suggesting the potential and diversity of molecular regulation of heterosis. In short, hybrid oyster DI has obvious hybrid advantages in growth and stress resistance, POD genes, notably TCF7L2 and SLC12A1, are proposed as selectable markers for high-yield, stress-resilient oyster lines, and our findings provide the necessary theoretical perspective for a deep understanding of the hybrid advantages of oysters and their generation mechanism.

Crassostrea hongkongensis is popular in southern China for its white flesh color, unique flavor, and delicious taste. However, the disadvantages of slow growth, poor tolerance, and high mortality limit its production and market sales. The application of genetic breeding techniques to breed new breeding lines with fast growth and low mortality is an important approach to solve these industrial challenges, including interspecific backcross breeding. In this study, we established eight experimental groups (HH-C. hongkonggensis female x C. hongkonggensis male; HA-C. hongkonggensis female x C. ariakensis male; AA-C. ariakensis male x C. ariakensis; A/HA-C. ariakensis female x HA male; HA/HA-HA female x HA male; H/HA-C. hongkonggensis female x HA male; HA/H- HA female x C. hongkonggensis male and HA/A-HA female x C. ariakensis male), tracked and compared their phenotypic traits. The results confirmed that the hatching parameters of the interspecific backcross groups (HA/H, HA/A, H/HA and A/HA) were significantly lower than those of the pure parental progeny groups (HH and AA). Although HA/A did not always show a significant growth advantage in the larval stage, it exhibited the largest shell height during the marine culture period (except on the 210th day), and showed a significant shell height advantage on the 360th day (P < 0.05). Moreover, there were obvious backcross advantages during the marine culture period, with backcross advantages (BAs) in shell height of 7.30 %, 17.66 %, 16.44 % and 10.95 % from the 90th to the 360th days, respectively. In addition, HA/A consistently ranked in the top three in terms of the incremental survival rate, being significantly higher than the grandparental offsprings (HH and AA), with HA/A showing the highest survival rates on the 210th and 360th days. Similarly, backcross advantages were observed at all time points, with BAs of 3.42 %, 5.96 %, 6.29 % and 0.43 %, respectively. Gonad development statistics and paraffin section results showed that all backcross groups were fertile and produced many normal gametes, with little difference in the ratios of males to females among the eight groups. In summary, the HA/A group showed significant backcross advantages in both growth and survival, with the best overall performance. This makes it a promising new strain that could help address the industrial problems of C. hongkongensis and has the potential for large-scale application.

C. dianbaiensis, a newly developed oyster variety, is characterized by rapid growth and strong resistance. Hybrids produced by crossing C. dianbaiensis females with C. iredalei males (DI) exhibit significant hybrid vigor. Backcrossing these hybrids with their parental species aims to transfer beneficial traits to the next generation. This study involved interspecific backcrossing of DI with both parental species, generating the following crosses: single crosses (C. dianbaiensis female x C. dianbaiensis male, C. iredalei female x C. iredalei male, C. dianbaiensis female x C. iredalei male), F2 hybrids (DI female x DI male), male backcrosses (C. dianbaiensis female x DI male, C. iredalei female x DI male), and female backcrosses (DI female x C. dianbaiensis male and DI female x C. iredalei male). The results confirmed successful bidirectional fertilization in both DI and backcrosses with parental species. In the planktonic larval stage, the backcross progeny exhibited no superiority (S) compared to the parental species, with a - 0.50 % reduction in shell height and a - 7.52 % decrease in cumulative survival rate. However, by day 360 of the grow-out phase, backcross progeny showed significant superiority (S), with increases in shell height (12.67 %), cumulative survival rate (18.53 %), and whole wet weight (3.66 %). In contrast, the F2 hybrids exhibited varying degrees of outbreeding depression (O) at day 360, with reductions in shell height (-14.27 %), cumulative survival rate (-16.40 %), and whole wet weight (-23.66 %). Although gonadal development in both backcross progeny and F2 hybrids lagged behind that of the parental species, they produced viable gametes. These findings demonstrate that backcrossing with both parental species helps maintain hybrid vigor in F1 progeny, providing a solid foundation for future genetic selection and the development of new commercial oyster populations in southern China.

The homeostasis of the intestinal microbiota of fish is beneficial to fish health, while food can affect the intestinal microbiota. Tilapia (Oreochromis spp.) has great economic value and is a good model to use in studying the digestion and absorption of nutrients. Furthermore, at present, due to a high demand and high price of high-quality feed raw materials, the nutritional composition of aquafeeds has been changing dynamically. There has yet to be a comprehensive review of research conducted on the influences of dietary macronutrients (proteins, lipids, and carbohydrates) on the tilapia intestinal microbiota. Therefore, this review focuses on the effects of dietary macronutrients on the gut microbiota of tilapia. Interestingly, we found that the best growth performance might not represent the best composition or functions of the gut microbiota. Overall, the unscientific addition of macronutrients to feed is harmful to the intestinal microbiota. Therefore, both growth performance and gut microbiota should be considered when evaluating certain macronutrients. It is our hope that this review will aid in regulating the intestinal microbiota of fish through nutritional means, thereby promoting tilapia farming.

To explore the histological and ultrastructural changes of the annual development of the testis and spermatogenesis of Lutraria sieboldii in Beibu Gulf of Guangxi,the annual development of testis and ultrastructure of spermatozoa of L.sieboldii were studied through tissue section,scanning and transmission electron microscopy.Results showed that the testis completes a cycle in one year,which can be divided into proliferating stage,growing stage,maturing stage,spawning stage and resting stage.The spawning was from December to April of the following year,and the testis development of 5%～10%individuals in each stage was slightly delayed.Spermatogenesis can be divided into proliferation period,growth period,mature period and metamorphosis period.The male reproductive cell can be divided into Spermatogonia stage,primary spermatocyte stage,secondary spermatocyte stage,spermatocyte stage and mature sperm stage.The sperm of L.sieboldii belongs to the flagella type,whose total length is(39.76±0.50)μm.The sperm head was composed of a nearly subelliptic spermatic acrosome and nucleus,the bottom of the acrosome and the spermatozoa connected with the spermatozoa were depressed to form a subacrosomal cavity.The electron density in the nucleus was uniform,and there was a gap in the middle of the nucleus.There are four mitochondria around the centriole complex to form the middle part of sperm,and the mitochondria are nearly round with apparent internal ridge.The plasma membrane wraps around the axial filaments to form sperm tail,and the"9 + 2"doublet microtubule structure can be clearly observed in the transverse section of the tail.In addition,there are two different types of spermatogonia:type A spermatogonia has no nucleolus in the nucleus while type B spermatogonia has nucleolus in the nucleus,and type B spermatogonia is distributed in the testis at different stages.