ROUNDUPS

• Review on genetic breeding progress of Bagridae family in China

  ZHAO Cheng, LI Yao, NING Xianhui, WANG Tao, YIN Shaowu

  2024,48(11):119601-119601, DOI: 10.11964/jfc.20230614062

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  Abstract:

  The Bagridae family constitutes an essential economic fishery resource in China, with species such as Pelteobagrus fulvidraco, Leiocassis longirostris, Pseudobagrus ussuriensis and P. vachelli possessing high production and economic value. Research into genetic breeding and germplasm enhancement is pivotal for fostering the sustainable development of China's aquaculture industry. This review systematically examines and projects the genetic breeding advancements of the Bagridae in China, encompassing selective breeding, hybrid breeding, cell engineering breeding, genetic engineering breeding and molecular marker-assisted breeding. The review aims to establish a theoretical foundation for the further scientific and rational exploitation of Bagridae family resources in China.

PAPERS

• Cloning, tissue expression and polymorphism of MHCⅡ gene of Gymnocypris przewalskii and Gymnocypris eckloni

  ZHANG Haichen, XU Baoke, A Linlin, MA Qinghua, GAO Qiang, TIAN wengen, YU luxian, LIANG Jian

  2024,48(11):119102-119102, DOI: 10.11964/jfc.20220413425

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  The major histocompatibility complex (MHC) is crucial in immune function regulation and is a primary factor in immune responses within organisms. To explore the characteristics and roles of this gene in Gymnocypris przewalskii, the full-length cDNA sequences of MHCⅡ and chaperone gene Ii were obtained by cloning using rapid-amplification of cDNA ends (RACE) technique. Meanwhile, the sequences of the coding regions of MHCⅡ and Ii in G. eckloni were also obtained and compared. Sequence alignment and analysis revealed that the characteristics of respective genes were largely identical in both species. The construction of phylogenetic tree indicated the closer evolutionary position of MHCⅡ in both fish, clustered to one family, Cyprinidae. The amino acid sequences of MHCⅡα/β from two species both contained a signal peptide, two functional domains, a transmembrane domain, in which a conserved structure found in many different species located, and a cytoplasmic region. Quantitative real-time PCR (qRT-PCR) results showed that MHCⅡ was highly expressed in the kidney, brain, gill, liver, and skin tissue around the anal fin of G. przewalskii, while the expression of which displayed a higher level in the brain, muscle, eye, and gill of G. eckloni. The expression of MHCⅡ in gill, kidney, liver, and intestinal tissues was also compared between normal and Saprolegnia infected individuals of G. przewalskii, results demonstrated that the expression level of 3 genes in MHCⅡ was significantly down-regulated in the kidney tissues, while α, β genes were significantly up-regulated in gill, liver and intestinal tissues. MHCⅡ mRNA levels were significantly reduced in gill and kidney tissues after different saline stress treatments on G. przewalskii. Gene polymorphism analysis indicated that MHCⅡα has 8 and 12 allelic genotypes, encoding 23 and 24 amino acid sequences in two species, respectively, with sequence polymorphisms primarily in the α1 functional region. MHCⅡβ had 12 and 14 allelic genotypes, encoding 22 and 23 amino acid sequences in two species, respectively. The lower polymorphisms in MHCⅡ α/β of G. przewalskii suggested a weaker association with salinity tolerance compared to G. eckloni. Genetic diversity analysis showed high population diversity in both species, with haplotype diversity approaching 1 and minimal differences in nucleotide diversity. The slightly higher haplotype and nucleotide diversity of the MHCⅡ in G. eckloni indicated a somewhat greater population stability compared to G. przewalskii. Our research verified that MHCⅡ not only plays an important role in immunologic defence of two kinds of fish but also involved in the salinity tolerance process of G. przewalskii, while gene polymorphisms were not highly associated with salinity tolerance.

• Functional analysis of mdh by CRISPR/Cas9 in blunt snout bream (Megalobrama amblycephala)

  GUO Dandan, ZHENG Guodong, CHEN Jie, ZOU Shuming

  2024,48(11):119603-119603, DOI: 10.11964/jfc.20191212093

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  Malate dehydrogenase gene (mdh) is closely associated with muscle growth, regulating muscle fiber growth and type transformation by influencing skeletal muscle energy metabolism. This study aimed to investigate the function and role of mdh in Megalobrama amblycephala by using CRISPR/Cas9 to knock-out the mdh and examining the phenotype and gene expression in the resulting mutants. The findings demonstrated that CRISPR/Cas9 can effectively knock-out mdh in M. amblycephala, with mutants exhibiting significant phenotypic differences from the control group. Mutants were notably smaller, with reduced body weight, length, height and width compared to controls. qPCR results showed that the expression level of mdh in the mutant individuals was significantly lower than that in the control group. In addition, the expression of MyoG, MyHCⅡa decreased significantly in mutants with reduced mdh, while MyHCⅡb showed no significant change. All the results suggest that CRISPR/Cas9 can be used for efficient and rapid gene editing. It also proved that the mdh gene may plays a promoting role in the growth of muscle in M. amblycephala, and the knock-out of mdh will inhibit the growth. The results of this study provide a certain theoretical value for the study of growth traits, which is conducive to the rational application of mdh in molecular breeding of M. amblycephala.

• Full-length transcriptome analysis of Pangasius sutchi

  HUAN Zhang, LI Dongyu, LI Weihao, GAO Jin, WANG Zhongduo, PAN Zhi, DONG Zhongdian

  2024,48(11):119604-119604, DOI: 10.11964/jfc.20220613562

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  Pangasius sutchi, a significant freshwater economic fish in Southeast Asia, is characterized by rapid growth, ease of cultivation, rich nutritional content, and the absence of small intermuscular bones. First introduced to China from Thailand in 1978, P. sutchi achieved a breakthrough in artificial breeding in 1997 and has since been extensively promoted in Guangdong, Guangxi, and Hainan provinces. Current research on P. sutchi primarily focused on breeding models, nutritional feed development, disease control, and fish product processing technology, with less emphasis on basic biology, particularly molecular biology. This study sequenced the full-length transcriptome from brain, gills, heart, liver, spleen, head kidney, stomach, intestines, gonads, and muscles of sexually matured P. sutchi using Single Molecule Real-Time (SMRT) sequencing on the PacBio Sequel platform to elucidate the genetic basis and support molecular biology research. A total of 1 487 336 high-quality reads were obtained, averaging 83 592 bp in length with an N50 of 162 901 bp. After self-correction, 1 005 955 CCS (Circular Consensus Sequence) were derived, and following filtration, 667 973 polyA-containing FLNC (full-length non-concatenated) were identified, averaging 2 057 bp in length with an N50 of 2 359 bp. For gene and transcript annotation, 614 078 (91.93%) FLNC were used, identifying 19 835 known genes and 9 348 novel genes. In addition, 50 311 ORF (open reading frame), 79 922 alternative splicing, 18 fusion genes, and 20 215 alternative polyadenylation sites were predicted. Of the 9 348 novel genes, 3 912, 2 385, 2 167, 81 and 1 520 were annotated in NR (non-redundant protein sequences), GO (gene ontology), KEGG (Kyoto encyclopedia of genes and genomes), KOG (eukaryotic orthologous groups) and SwissProt databases, respectively. GO enrichment analysis revealed that 1 309, 1 351, and 1 524 new genes were enriched in cellular process, cellular anatomical entities, and binding terms, respectively. KEGG enrichment indicated that the new genes were primarily enriched in cellular processes such as eukaryotes (106), signal transduction (276), folding, sorting and degradation (79), amino acid metabolism (63), and endocrine system (197). 4 624 lncRNA were obtained in P. sutchi, regulating 32 283 target mRNA. GO enrichment results showed that target mRNA were mainly enriched in cellular processes (12 084), cellular anatomical entity (18 034) and binding (12 772). KEGG analysis indicated that the target mRNA were predominantly enriched in the transport and catabolism pathway (1 437), signal transduction (4 165) pathway, folding, sorting and degradation (643) pathway, carbohydrate metabolism (584) pathway and immune system (2 135). In this study, the full-length transcriptome sequencing data analysis and functional annotation have enriched the genetic resources of P. sutchi and provided a basis for further research on the biological characteristics and gene function of P. sutchi.

• Cloning and function of prophenoloxidase activating factors gene from the epidermis of Macrobrachium nipponense

  PENG Yanxin, YUE Kaidi, DU Juan, NING Qianji

  2024,48(11):119105-119105, DOI: 10.11964/jfc.20220313414

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  Prophenoloxidase activation is a crucial innate immune response in crustaceans against pathogenic microorganisms infections, with prophenoloxidase-activating factors (PPAFs) being pivotal in this activation. Despite their importance, crustacean epidermal PPAFs have been seldom studied. To elucidate the role of epidermal PPAFs in crustaceans immunity, a novel PPAF gene, MnPPAF1 (GenBank accession: OP784577), was cloned and characterized from the epidermis of Macrobrachium nipponense using PCR and RACE techniques, based on prior transcriptome data. Bioinformatics, qPCR and RNAi methods were employed to analyze the gene sequence, spatial and temporal expression patterns, transcription levels of epidermal MnPPAF1, phenoloxidase (PO) activity, and shrimps mortality following Aeromonas hydrophila challenge. The complete MnPPAF1 cDNA sequence is 1 718 bp, encoding a 460-amino acid protein with clip-domain serine proteinase (Clip-SP) and trypsin-like serine protease (Tryp-SP) domains. MnPPAF1 expression was detechted in various tissues, including ventral and dorsal epidermis, hemocytes, gills, stomach, heart, hepatopancreas, with epidermal expression correlating to the molting cycle. Expression levels in the later premolt stage (D₄ stage) were 857% higher than in the intermolt stage (C stage). After A. hydrophila challenge, epidermal MnPPAF1 expression peaked at 6 h, increasing by 227% over the control group, while epidermal PO activity peaked at 12 h, increasing by 24%. 3 μg of dsRNA solution was injected into the second segment of the abdomen and back every 12 h, 3 injections in total. RNAi has the highest interference efficiency 12 h after the last injection, where the expression of epidermal MnPPAF1 decreased by 71.79%, compared to the control group, and after 24 h, the activity of epidermal PO decreased by 72.31%. Challenge at the time point with the highest interference efficiency and within 120 h, the cumulative mortality of shrimp in the challenged + RNAi group increased by 26% compared with that in the challenged + non-RNAi group. These findings indicate that MnPPAF1, an important immune factor in the epidermis, was involved in regulating the activation of the prophenoloxidase system. The down-regulation of this gene expression can significantly increase the mortality of shrimp infected by A. hydrophila. This study contributes to a better understanding of the epidermis's role in the crustaceans immune system.

• Cloning, sequence analysis of the NR1 gene of Onchidium reevesii and low frequence sound stimulation on gene expression

  QIAN Chang, XIAO Haiming, CHEN Xilin, ZHANG Xiaoming, TU Zhihan, SHEN Heding

  2024,48(11):119606-119606, DOI: 10.11964/jfc.20220313352

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  NMDA receptors (N-methyl-D-aspartic acid receptor, NMDAR) are members of ionotropic glutamate receptor family, widely distributed in central nervous system, and play a pivotal role in auditory pathway. NR1 is the fundamental subunit necessary for the NMDAR complex. The life activities of Onchidium reevesii are closely related to tidal cycles. In this study, we used low-frequency sound to stimulate the O. reevesii and investigated the expression of NR1 receptor gene in its ganglion. The NR1 gene's cDNA sequence was cloned using RACE-PCR on nervous tissue from O. reevesii, followed by bioinformatics analysis and qRT-PCR experiments. We then stimulated O. reevesii in the laboratory by simulating the low-frequency sounds of the tides, and measured NR1 gene expression under different frequencies of sound stimulation. The full-length cDNA sequence of NR1 gene was 2 434 bp, comprising a 357 bp 5'non-coding region, a 184 bp 3'non-coding region, and a 1 893 bp open reading frame encoding 630 amino acids. The cloned receptors contain a signal peptide, predicted binding sites for glycine and glutamate, a recognized transmembrane region. Multi-sequence alignment revealed high conservation of NR1 across species. A phylogenetic tree indicated that the NR1 gene of O. reevesii is related to that of Aplysia california, aligning with traditional morphological classification. The results of qRT-PCR showed that OrNR1 was expressed in different tissues, but the relative expression level in ganglion was significantly higher than that in other tissues, followed by the pleopod and liver, and the expression level in the mouthparts and dorsal skin were low (P<0.05). The expression level of OrNR1 was higher than the control group at 200 and 160 Hz (P<0.05); the expression of OrNR1 gene was inhibited at 120 Hz, the expression levels of different frequencies were significantly differently(P<0.05). We hypothesize that the OrNR1 gene plays an important role in the low-frequency sound perception of O. reevesii.

• Effects of salinity acclimation on physiology and biochemistry and antioxidant immunity of juvenile Luciobarbus capito

  LI Haitao, ZHAO Zhigang, XU Wei, LUO Liang, SHANG Xinchi, LI Mingshuai, LIU Jinyu, WANG Yu, ZHANG Rui, GUO Kun, GENG Longwu, ZHANG Qing, DU Rujun, CONG Yanfeng

  2024,48(11):119107-119107, DOI: 10.11964/jfc.20220413471

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  In saltwater fish culture, directly releasing freshwater-cultured fry into medium to high salinity water typically results in high mortality due to environmental adaptation challenges. However, prior adaptive acclimation in low to medium salinity environments can enhance fry resistance and improve survival rates. This study investigated the physiological, biochemical, and immune stress responses of Luciobarbus capito following salinity acclimation. Juvenile fish, averaging (15.09±3.54) cm in length and (13.66±1.26) g in weight, were divided into three groups: a control group maintained in freshwater, an acclimated group preconditioned at 4 g/L salinity for 168 hours before exposure to 8 g/L saltwater, and a non-acclimated group directly introduced in 8 g/L saltwater. Physiological, biochemical, and immune stress indicators were measured at 0, 6, 12, 24, 48, 96 and 168 h in all groups. The results indicated that, (i) the blood routine indexes (WBC, Lymph, Mon, Gran, RBC, HGB contents), plasma physiological and biochemical indexes (UREA concentration, GLU-G and ALB contents, plasma osmotic pressure), ACP, AKP, LDH in gill tissue and antioxidant indexes (SOD, CAT, GSH-Px, MDA content) in liver tissue of acclimated group and non-acclimated group all showed an increasing first and then decreasing with the extension of stress time. (ii) In the early stage of salinity stress, the biochemical indexes of juveniles in both acclimated and non-acclimated groups reached their peak at the same time. However, the amplitude and peak size of the physiological and biochemical indexes (WBC, Lymph, Gran, Mon, Urea, GLU-G, ALB, osmotic pressure), transaminases (AST, ALT) and antioxidant enzymes (SOD, CAT, GSH-Px, MDA) of liver tissue were significantly lower than those of non-acclimated group (P<0.05). (iii) After 7 days of 8 g/L NaCl salinity stress, both the acclimated and non-acclimated could recover to the level of the control group, but the plasma osmotic pressure and plasma ALB content of the L. capito juvenile in the acclimated group recovered to the level of control group earlier than those in the non-acclimated group. The study's findings suggest that L. capito juveniles acclimated at 4 g/L salinity exhibit superior physiological and biochemical self-regulation and recovery ability when subjected to 8 g/L salinity stress.

• Microscopic observations on karyokinesis and cytokinesis in the gametophytes of Saccharina japonica

  ZHENG Qian, QIAO Yaming, BI Yanhui, ZHOU Zhigang

  2024,48(11):119108-119108, DOI: 10.11964/jfc.20220413429

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  Gametophyte clones of Saccharina japonica can be established through the induction of mitosis in gametophytes under artificial culture conditions. However, there have been few reports on the cytological characteristics of mitosis in these clones. This study presents the first observation of the cellular structure during the mitosis phases of kelp gametophytes using paraffin sections, immunofluorescence technique coupled with DAPI staining. Changes in the size and morphology of the gametophyte nucleus during the phases of mitosis were clearly illustrated by DAPI staining. The spindle fibers, originating from the centrosome, and cage-shaped spindle were successfully visualized. Ultrathin sections revealed cleavage furrows at the positions of cell plates under a transmission electron microscope. These furrows, with closed curved front ends formed by invagination of the plasmalemma, grew centripetally until they contacted and fused, leading to the construction of a new cell wall and completion of cytokinesis. The chromosomes of the gametophyte cell were prepared by pressing method, stained with hematoxylin and counterstained with DAPI. It was confirmed that there were 31 chromosomes in the gametophyte of S. japonica. The characterizations of mitosis of S. japonica gametophytes including karyokinesis and cytokinesis were firstly observed in the study, and chromosomes in the intact cell of gametophyte were also illustrated. It provided accurate data for the cytogenetic study of S. japonica, and provided new evidence for the study of cytoplasmic division of brown algae.

• Differences of carotenoid composition in thallus and conchocelis of Neoporphyra haitanensis

  PAN Haibin, TANG Xinyi, CHEN Haimin, YANG Rui, ZHANG Peng, LUO Qijun, CHEN Juanjuan

  2024,48(11):119109-119109, DOI: 10.11964/jfc.20220613572

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  Carotenoids, essential photosynthetic pigments and antioxidants, regulate plant growth, development and environmental adaptation. This study aimed to elucidate the carotenoid responses in Neoporphyra haitanensis at different growth stages by analyzing carotenoid compositions in conchocelis and thallus across various generations and harvest stages using ultra-liquid chromatography-triple quadrupole mass spectrometry. Optimal extraction conditions were determined as methanol-dichloromethane (1∶1, V/V) as the solvent, a solid-to-liquid ratio 1∶10, and a 30 min ultrasonic time. Liquid chromatography parameters were optimized to achieve a resolution of 1.5 for 16 carotenoids, with a detection limit of 1.57-4.96 ng/mL. Eight carotenoids were detected in two generations of N. haitanensis, associated with the α-carotene synthesis pathway (α-carotene, ε-carotene, α-cryptoxanthin and lutein) and the β-carotene synthesis pathway (β-carotene, β-cryptoxanthin, zeaxanthin and antherxanthin). The total carotenoid content and the photochemical efficiency (F_v/F_m) in the thallus were 1.4- and 1.5-fold higher, respectively, than in the conchocelis. Notably, β-cryptoxanthin content in conchocelis, which has a stable growth state and low antioxidant requirements, was 3.7 times higher than thallus, while the contents of α-carotene, β-carotene, ε-carotene, zeaxanthin, lutein and α-cryptoxanthin were 22.7%-67.0% of those in the thallus. Zeaxanthin and lutein were the predominant carotenoids in the thallus. Except for β-carotene, the contents of the other seven carotenoids decreased with the extension of the harvest period. The study indicates that carotenoid content is closely related to the growth stage and survival environment of N. haitanensis. Rapid carotenoid synthesis in the early thallus period is likely a response to strong light and high temperature stresses, facilitating stress defense and growth. Conversely, a decreased synthesis rate in conchocelis and the late thallus period suggests a reduced antioxidant requirement. These findings provide valuable experimental data for further development of cultivars and seaweed farming practices.

• Detection and empty volume measurement and calculation method of artificial reef groups in marine pastures

  YANG Long, GAO Shan, FENG Yikai, LIU Senbo, JIANG Fengbiao, DING Jisheng

  2024,48(11):119510-119510, DOI: 10.11964/jfc.20230514029

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  In recent years, the rapid development of social economy and a sharp increase in resource demand have spurred rapid growth in the construction of marine ranching. The deployment of artificial fishing reefs during marine ranch construction and their subsequent status monitoring are crucial. Monitoring encompasses not only the distribution range and condition of artificial fishing reefs and the scouring of the surrounding seabed but also the verification of the effective spatial volume of the deployed artificial fishing reefs to compliance with technical indicators during marine ranch construction. This paper exemplifies the detection and empty volume calculation of artificial reefs to ascertain their location and volume. Initially, a high-resolution Multibeam Echo sounder sonar system (integrated with high-precision attitude measurement system) and a high-precision Global Navigation Satellite System are employed to accurately capture the underwater location, shape, and seabed topography of artificial reefs. Subsequently, various volume calculation methods are analyzed based on the geospatial data obtained from precise measurements. An optimal method is then selected to calculate the volume of the artificial reefs and compared with the actual volume. The results indicate a high consistency between the method used in this study and the actual location of the artificial reef. For empty volume calculation, the error was 25.76% for a long-standing reef, while it was only 2.22% for a newly placed one. This study demonstrates that the method can accurately determine the location and morphology of artificial reefs and accurately calculate the empty volume for new artificial reefs. However, due to factors such as scouring and subsidence, discrepancies are observed in the calculations for long-standing artificial reefs. The findings also confirm that the integrated use of sonar and high-precision positioning equipment is effective for an objective and equitable evaluation of marine pastures construction.

• Prediction on fishing ground of Ommastrephes bartramii in Northwest Pacific based on deep learning

  XIE Mingyang, LIU Bin, CHEN Xinjun

  2024,48(11):119311-119311, DOI: 10.11964/jfc.20220413451

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  Neon flying squid (Ommastrephes bartramii) is a primary economic cephalopod species in the Northwest Pacific Ocean. Accurate identification the spatial distribution of fishing ground provides a scientifically sound and effective foundation for fishery production. In the era of big data in marine fisheries and marine remote sensing, extracting and mining valuable information from vast datasets has emerged as a significant challenge in forecasting fishing grounds. Consequently, this study utilizes the theories of deep learning and fisheries oceanography, utilizing sea surface temperature (SST) data as input to develop a U-Net model for discriminating central fishing grounds from July to November in 1998-2019. The results indicate an accuracy of 86.7% for the validation set, 89.7% for the training set, and the accuracy, precision, recall and balanced F1-score values for the 2020 test set being 87.2%, 0.91, 0.87 and 0.89, respectively. The catch data from fisheries is largely consistent with the predicted central fishing grounds, and the model's application proved effective. Across various climatic conditions, the model demonstrates robust adaptability. The latitude of the central fishery shifts southward during El Niño event and shifts northward during La Niña events. The model constructed in this study can effectively address the problem of fishery discrimination under complex data set, improve the precision of fishing ground prediction models, and lay a theoretical basis and foundation for the realization of fishing ground prediction. It holds promising application prospects.

• Effect of preservation temperature on the nitrification performance and morphological structure of bioflocs

  JIANG Zejian, LIU Wenchang, TAN Hongxin, LUO Guozhi, SUN Dachuan

  2024,48(11):119512-119512, DOI: 10.11964/jfc.20220113285

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  This study aimed to determine the optimal storage temperature for bioflocs. A One-Way experimental design was employed, where bioflocs were stored at room temperature (25 °C), refrigerated (4 °C) and frozen (-20 °C) for periods of 7, 14, 21 and 28 d. The nitrification performance of bioflocs declined under all three conditions as storage time increased. After 28 d, the ammonia oxidation rate at 4 °C was (0.16±0.10) mg/(L·h), significantly higher than the rates at 25 °C (0.08±0.09) mg/(L·h) and -20 °C (0.01±0.09) mg/(L·h). Bioflocs stored at -20 °C had almost no ammonia oxidation activity by day 7, with a 99.52% reduction from the initial rate. The nitrite oxidation rate at 4 °C after 28 d was (0.19±0.03) mg/(L·h), which was significantly higher than that of bioflocs stored at 25 °C (0.10±0.05) mg/(L·h) and -20 °C (0.14±0.02) mg/(L·h). Microscopic observation revealed that of bioflocs stored at 25 °C became looser, with a decrease in volume average size from (245.92±21.51) μm to (148.50±9.90) μm by day 28. Conversely, bioflocs stored at -20 °C increased in size from (245.92±21.51) μm to (310.82±29.67) μm. No significant changes in structure or particle size were observed for bioflocs stored at 4 °C. In conclusion, a storage temperature of 4 °C is recommended for bioflocs. This study provides insights into appropriate storage conditions and duration, which can inform the storage and reuse of bioflocs in practical applications.

• Effect of replacing glucose with soybean oligosaccharides on microbial community structure in biofloc system

  ZHOU Hangxian, TAO Mingwei, WEI Jie, ZHAO Jianhua, XU Qiyou

  2024,48(11):119613-119613, DOI: 10.11964/jfc.20230614058

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  The study investigated the effects of soybean oligosaccharides (SBOS) on the microbial community structure within a biofloc system and identified the optimal concentration. The control group utilized glucose as carbon source, whereas experimental groups replaced it with 2.5%, 5.0%, 7.5%, and 10.0% SBOS, respectively. Ammonium chloride served as the nitrogen source with C/N ratio of 15, and Bacillus subtilis was introduced to establish the biofloc system. The results indicated that total nitrogen, ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen concentrations in the water were reduced, with no significant differences observed among all groups (P>0.05). High-throughput 16S rRNA sequencing revealed that Proteobacteria was the dominant phylum at 14 days in both experimental and control groups. By 28 days, Proteobacteria and Bacteroidota proportions were similar. At the genus level, Bacillus abundance significantly increased in the SBOS-2.5 and SBOS-10.0 groups at 14 days (P<0.05), while Aeromonadaceae abundance significantly decreased (P<0.05). At day 28, Flavobacterium abundance significantly increased in the SBOS-2.5 and SBOS-10.0 groups compared to the control group (P<0.05). Additionally, Chryseobacterium abundance in all experimental groups was significantly lower than control group (P<0.05). Some bacteria may be crucial in the nitrification and denitrification of nitrogen in water, according to a correlation analysis between bacterial composition and environmental conditions. In conclusion, substituting glucose with 2.5% and 10.0% SBOS as the carbon source in bioflocs effectively enhanced the abundance of beneficial bacteria and reduced that of harmful bacteria, thus promoting the stability of bacterial communities in water. Considering experimental outcomes and application costs, a 2.5% SBOS replacement ratio for glucose is recommended. This study provides a foundation for the practical application of SBOS as a carbon source in the biofloc systems and offers insights for future research.

• Predation by two species of crabs on different sizes of juvenile sea urchin Salmacis sphaeroides

  TU Youkai, HONG Zesen, WU Hong, YU Zonghe

  2024,48(11):119614-119614, DOI: 10.11964/jfc.20221113784

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  The sea urchin species Salmacis sphaeroides holds significant ecological and economic value in the South China Sea. However, natural populations are increasingly at risk due to environmental pollution, overfishing, climate change and other factors. Stock enhancement through breeding and release could mitigate this decline, but crab predation poses a significant threat to released individuals. The predation effects on juvenile S. sphaeroides and the factors influencing these effects are not well understood. This study investigated the predation of two sizes classes of juvenile S. sphaeroides [test diameters: large, (36.50±4.11) mm；small, (22.33±1.97) mm] by Charybdis japonica and Thalamita crenata, both of which are prevalent in the South China Sea, using both indoor and filed trapping experiments. Results indicated that S. sphaeroides size and predation duration were key factors influencing predation rates, with species-specific differences between the two crab species. C. japonica exhibited high predation rates on small juveniles at both 0-24 and 24-48 h, with rates of (3.75±1.09) ind/d and (3.75±1.30) ind/d, respectively, while predation on large juveniles was significantly lower at (0.50 ±0.86) ind/d and (0.25±0.50) ind/d, respectively. In 0-24 h, T. crenata showed a high initial predation rate on small juveniles of (4.25±3.27) ind/d at 0-24 h, which decreased to (2.00±1.58) ind/d during 24-48 h, and exerted minimal pressure on large juveniles. Field trapping experiments revealed a strong attraction of juvenile S. sphaeroides to C. japonica, with an average capture rate of (2.40±0.89) ind/(cage·d). This study concludes that crabs are the primary predators of S. sphaeroides, and to enhance restocking efficiency, it is recommended to release large-sized sea urchin seedlings and to control potential predators such as crabs in advance.

• Effects of replacing fish meal with black soldier fly larvae meal on serum immune antioxidant indices, intestinal function and disease resistance of hybrid snakehead (Channa maculata ♀×Channa argus ♂)

  XIE Yutong, HUANG Wenqing, LI Shiyang, HUANG Yanhua, LIU Chun, XU Fengmeng, WANG Guoxia

  2024,48(11):119615-119615, DOI: 10.11964/jfc.20230514017

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  Abstract:

  Fish meal is a prevalent source of animal protein in aquatic feed, yet its high cost and an import reliance of up to 80% have hindered the sustainable growth of aquaculture in our country. Thus, it is imperative to identify alternative proteins to replace fish meal. This study aimed to assess the impact of substituting fish meal with black soldier fly larvae meal (BSFLM) on the immune antioxidant status, intestinal flora and disease resistance of hybrid snakehead fish. Five isonitrogenous and isolipid diets were formulated, with fish meal replaced by 7.5% (BSFLM7.5), 15.0% (BSFLM15), 22.5% (BSFLM22.5) and 30.0% (BSFLM30) BSFLM, corresponding to 48.8, 97.6, 146.4 and 195.2 g/kg BSFLM, respectively. A total of 525 hybrid snakeheads with an average body weight of (10.84±0.01) g were randomly assigned to 5 groups, each with 3 replicates 35 fish per replicate. The results indicated that the alkaline phosphatase (AKP) activity in the BSFLM30 group was higher than in the BSFLM7.5 and fish meal (FM) groups (P<0.05). The malondialdehyde (MDA) levels in the BSFLM22.5 group were lower than those in the FM group (P<0.05). No significant differences were observed in the activities of lysozyme (LZM), catalase (CAT), superoxide (SOD), total antioxidant capacity (T-AOC), and glutathione peroxidase (GSH-Px) among all groups (P>0.05). The richness estimators Sobs, Chao, Ace, as well as Shannon and Simpson diversity indices of the intestinal content flora in the BSFLM15-BSFLM30 groups, were lower than those in the FM and BSFLM7.5 groups (P<0.05), indicating a decrease in species diversity. The relative abundance of Chlamydiae, Proteobacteria, Spirochaetes, Ralstonia and Pseudomonas in the experimental groups was lower than in the control group (P>0.05). Conversely, the BSFLM30 group exhibited higher Sobs, Chao, and Ace indices of intestinal flora compared to the FM and other experimental groups (P<0.05). The relative abundance of Bacteroidetes, Firmicutes, Paludibacter and Sedimentibacter was greater in the BSFLM30 group than in the other groups (P>0.05). The relative abundance of Spirochaetes, Proteobacteria and Ralstonia was lower in the experimental group than that in the control group (P>0.05). The mortality rate following Aeromonas schubertii infection was significantly lower in the BSFLM7.5, BSFLM7.5 and BSFLM22.5 groups than in the FM and BSFLM30 groups (P<0.05). In conclusion, dietary supplementation with BSFLM can enhance immune antioxidant capacity, microbial structure of intestinal contents, increase microbial diversity, improve intestinal function, and bolster resistance to A. schubertii infection. However, the replacement levels should not exceed 22.5%.