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The ivory shell Babylonia areolata is an economically important marine benthic gastropod known for its rapid growth and high nutritional value. B. areolata is distributed in Southeast Asia and the southeast coastal areas of China. In this study, we constructed a high-quality genome for B. areolata using PacBio, Illumina, and Hi-C sequencing technologies. The genome assembly comprised 35 chromosomal sequences with a total length of 1.65 Gb. The scaffold and contig N50 lengths were 53.17 Mb and 2.64 Mb, respectively, with repeat sequences constituting 64.46% of the genome. Furthermore, 26,130 protein-coding genes and 96.75% of the genome's BUSCOs were identified. This inaugural report of a B. areolata genome provides crucial foundational information for further investigations into the biology, genomics, and genetic improvement of economic traits of this species. [ABSTRACT FROM AUTHOR]

The decline in dissolved oxygen concentrations has been one of the most important changes occurring in the oceans, greatly impacting the survival, abundance, development, metabolism, growth, and reproduction of aquatic organisms. Aquaculture has suffered from coastal seawater deoxygenation, and the micro-environments of aquaculture systems also contribute to the frequent occurrence of hypoxic events. The cultivation of hypoxic-tolerant species and varieties will be urgent for the sustainable development of aquaculture. In this review, the current and ongoing research topics on hypoxia tolerance of aquatic animals were summarized and discussed, including the physiological mechanisms of hypoxia tolerance and the genetic and epigenetic sources of hypoxia tolerance differences in aquatic animals. Understanding the results of these two aspects will allow us to shape aquatic animals' tolerance to hypoxia and create hypoxia-tolerant aquaculture species and varieties by cutting-edge breeding techniques. This will help us alleviate the ecological damage and economic losses brought on by hypoxia occurrences. We urge those working in the aquaculture field to understand the negative effect that hypoxia has on aquaculture systems. We also encourage future research that uses aquaculture systems as ones of the models for studying environmental hypoxia and biological hypoxia responses and adaptation. [ABSTRACT FROM AUTHOR]

The tremendous expansion of Chinese abalone production has not been without challenges such as low salinity stress, which may occur during severe summer rainstorms and typhoon events. Interspecific hybrids have, however, been of great use to the aquaculture industry in withstanding environmental stresses. This study adopted the non-invasive method of measuring heart rate to monitor the cardiac performance of the Pacific abalone and two of its interspecific hybrids during the incidence of continuous salinity decrease. The results showed that low salinity significantly influences the heart rate of abalone. Fluctuation in the abalone's heartbeat suggests a pattern with three phases and two breakpoints of salinity (BOS1 and BOS2). BOS1 represents an isosmotic point, and BOS2 represents lethal salinity. We argue that relatively lower BOS suggests better tolerance to low salinity, and long-term exposure to salinities around BOS2 could be detrimental to all three species. The hybrid H. discus hannai ♀ x H. fulgens ♂ (DF) recorded the lowest BOS1 and BOS2, which was also significantly different (P = 0.01) from DD at BOS1, suggesting a better tolerance potential for low salinities than the other species. Altogether, our data establish species-specific BOS and reveal the cardiac mechanism by which abalone responds to low salinity. The results confirm that the non-invasive heart rate detection method could likewise be adopted to define critical salinities for abalone, and hybridization could be a potential method to breed the more stress-resilient aquatic animals. [ABSTRACT FROM AUTHOR]

Pacific abalone, Haliotis discus hannai, is an economically important marine mollusk species and an important model animal for studies on ecological, fertilization and developmental biology. While embryonic injection and genome editing have been wildly used in gene function study and trait improvement in many species, they have not been developed in abalones. In this study, we reported an effective method to inject exogenous materials in H. discus hannai unfertilized eggs. The injected eggs could be fertilized at a ratio of 52.6% ± 5.9% and hatch at a ratio of 14.6% ± 1.6%. On the base of this, we further developed an efficient genome editing approach in this species with the transcription activator-like effector nuclease (TALEN) technique. Two TALEN pairs targeting the coding sequence of the abalone nodal gene were assembled and tested. While one of the TALEN pairs showed no detectable mutation efficacy, the other one generated mutations in 50% of the targeted loci. The mutation includes small insertions and deletions and base pair replacements like that reported in other species when the TALEN method was applied. Overall, this is the first study to demonstrate site-specific genome editing in abalone. This work can serve as a reference for future studies focusing on the functional genomics in mollusks. [ABSTRACT FROM AUTHOR]

Recently, mass mortality affected the cultured small abalone, Haliotis diversicolor diversicolor, which was the dominant cultured abalone species in southern China. Prior studies revealed that survivorship varied significantly between different stocks and crosses. However, the immunological basis for differences in susceptibility has not been well understood to date. Herein, low temperature, air exposure tolerance tests, and pull-off force measurement were assessed in the three groups (Japan, Taiwan, and their Hybrid stock). The results showed that the critical thermal minimum (CTMin) at 50% was 15.6 °C for the Taiwan stock, 12.1 °C for the Japan stock, and 13.2 °C for the Hybrid stock. Upon air exposure challenge, 100% abalones from the Taiwan group died after 8 h at 24 °C, while the survival rate in the Japan and Hybrid groups were 37.8% and 29.4%, respectively. The detachment stress for the Japan group was 42.3 kPa, which was 2.78-fold and 1.43-fold higher compared to the Taiwan and Hybrid groups, respectively. Variation in susceptibility to disease may be based on the effectiveness of the innate immune responses. Therefore, total hemocyte count, phagocytosis, respiratory burst, superoxide dismutase activity, acid phosphatase activity, alkaline phosphatase activity, and myeloperoxidase activity were determined for the healthy abalones in each group. Positive mid-parent heterosis on immunological parameters was consistent with the prior knowledge on the positive mid-parent heterosis for survival rate, which indicated the improvement on immune reaction and disease resistance through hybridization methods. The current study will be useful in efficient design of breeding programs for the development of sustainable abalone aquaculture. [ABSTRACT FROM AUTHOR]

Ivory shell, Babylonia areolata, is one of the commercially important mariculture species in China and South East Asia. Survival varies in the artificial hatching and larval rearing of B. areolata. Food deprivation may be involved in rearing mortality, and so, a better understanding of how larvae respond and adjust to starvation is needed. In this study, the metabolite profiles of newly hatched larvae with yolk (I), larvae with yolk exhaustion (II), larvae suffering 24 h starvation after yolk exhaustion (III), and larvae fed with exogenous nutrients after yolk exhaustion (IV) were analyzed by LC-MS/MS. Principal component and cluster analyses revealed differential abundance of metabolite profiles across groups. When compared to metabolite levels of the I group, significantly up-regulated metabolites included polyunsaturated fatty acids, phospholipids, nucleotide, amino acids, and their derivatives were found in the II group, indicating that organisms relied predominantly on glycerophospolipid metabolism and protein-based catabolism for energy production during this stage. During starvation after yolk exhaustion, the levels of all energy related metabolites were significantly reduced, but an increase in products of purine and pyrimidine metabolism indicated an insufficient energy supply and an increase in cellular disintegration. Larvae fed exogenous nutrients can have significantly improved metabolism compared to starved larvae. These findings suggest that metabolomics, using LC-MS/MS, can be used to assess the physiological status and food-affected metabolic changes affecting B. areolata larvae. [ABSTRACT FROM AUTHOR]

The small abalone ( Haliotis diversicolor) is one of the most important aquaculture species in East Asia. To facilitate gene cloning and characterization, genome analysis, and genetic breeding of it, we constructed a large-insert bacterial artificial chromosome (BAC) library, which is an important genetic tool for advanced genetics and genomics research. The small abalone BAC library includes 92,610 clones with an average insert size of 120 Kb, equivalent to approximately 7.6× of the small abalone genome. We set up three-dimensional pools and super pools of 18,432 BAC clones for target gene screening using PCR method. To assess the approach, we screened 12 target genes in these 18,432 BAC clones and identified 16 positive BAC clones. Eight positive BAC clones were then sequenced and assembled with the next generation sequencing platform. The assembled contigs representing these 8 BAC clones spanned 928 Kb of the small abalone genome, providing the first batch of genome sequences for genome evaluation and characterization. The average GC content of small abalone genome was estimated as 40.33 %. A total of 21 protein-coding genes, including 7 target genes, were annotated into the 8 BACs, which proved the feasibility of PCR screening approach with three-dimensional pools in small abalone BAC library. One hundred fifty microsatellite loci were also identified from the sequences for marker development in the future. The BAC library and clone pools provided valuable resources and tools for genetic breeding and conservation of H. diversicolor. [ABSTRACT FROM AUTHOR]

Caspases have been demonstrated to possess important functions in apoptosis and immune system in vertebrate. But there is less information reported on the oyster larval development. In the present work, two full-length molluscan caspase genes, named Cacaspase- 2 and Cacaspase- 3, were characterized for the first time from Fujian oyster, Crassostrea angulata. Which respectively encode two predicted proteins both containing two caspase domains of p20 and p10 including the cysteine active site pentapeptide 'QACRG' and the histidine active site signature. Otherwise Cacaspase- 2 also contains a caspase recruitment domain. Homology and phylogenetic analysis showed that Cacaspase- 2 shared high similarity with initiator caspase- 2 groups, but Cacaspase- 3 clustered together with executioner caspase- 3 groups. Cacaspase- 2 and Cacaspase- 3 mRNA were both highly expressed in gills and labial palp and were significantly expressed highly in larvae during settlement and metamorphosis. Through the whole mount in situ hybridization, the location of Cacaspase- 2 is in the foot of the oyster larvae and the location of Cacaspase- 3 is in both the foot and velum tissues. These results implied that Cacaspase- 2 and Cacaspase- 3 genes play a key role in the loss of foot and Cacaspase- 3 gene has an important function in the loss of velum during larvae metamorphosis in C. angulata. [ABSTRACT FROM AUTHOR]

The small abalone, Haliotis diversicolor, is an economically important shellfish species in East Asia. The wild stocks have been highly threatened due to overfishing in the past several decades. Taking into account conservation and recovery of wild resources, long preserved samples were used to analyze population structure. However, extreme fragmentation of DNA limited the use of these degraded DNA samples. In this study, a total of 96 novel single nucleotide polymorphisms (SNPs) were identified based on transcriptomes of H. diversicolor. The parallel target sequencing was then used to examine one wild population collected in 2003 from Sanya Bay, Hainan Province with degraded DNA. Nineteen loci appeared in more than 80% of individuals and were polymorphic. This study provides a valuable method for using degraded DNA and molecular markers for genetic diversity analysis of H. diversicolor. [ABSTRACT FROM AUTHOR]

Seafood coloration is typically considered an indicator of quality and nutritional value by consumers. One such seafood is the Xishi abalone (Haliotis gigantea), which displays muscle color polymorphism wherein a small subset of individuals display orange coloration of muscles due to carotenoid enrichment. However, the metabolic basis for carotenoid accumulation has not been thoroughly investigated in marine mollusks. Here, GC-TOF-MS-based untargeted metabolite profiling was used to identify key pathways and metabolites involved in differential carotenoid accumulation in abalones with variable carotenoid contents. Cholesterol was the most statistically significant metabolite that differentiated abalones with orange muscles against those with common white muscles. This observation is likely due to the competitive interactions between cholesterol and carotenoids during cellular absorption. In addition, the accumulation of carotenoids was also related to fatty acid contents. Overall, this study indicates that metabolomics can reflect physiological changes in organisms and provides a useful framework for exploring the mechanisms underlying carotenoid accumulation in abalone types. [ABSTRACT FROM AUTHOR]

Long non-coding RNAs (lncRNAs) are known to play a major role in the epigenetic regulation of muscle development. Unfortunately there is little understanding of the mechanisms with which they regulate muscle growth in abalone. Therefore, we used RNA-seq to study the muscle transcriptomes of six Haliotis discus hannai specimens: three large (L_HD group) and three small (S_HD group). We identified 2463 lncRNAs in abalone muscle belonging to two subtypes: 160 anti-sense lncRNAs and 2303 intergenic lncRNAs (lincRNAs). In the L_HD group, we identified 204 significantly differentially expressed lncRNAs (55 upregulated and 149 downregulated), and 2268 significantly differentially expressed mRNAs (994 upregulated and 1274 downregulated), as compared to the S_HD group. The bioinformatics analysis indicated that lncRNAs were relate to cell growth, regulation of growth, MAPK signaling pathway, TGF-β signaling pathway, PI3K-Akt and insulin signaling pathway, which involved in regulating muscle growth. These findings contribute to understanding the possible regulatory mechanisms of muscle growth in Pacific abalone. [ABSTRACT FROM AUTHOR]

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper. [ABSTRACT FROM AUTHOR]

The ivory shell, Babylonia areolata , is a commercially important aquaculture species in the southeast coast of mainland China. The middle veliger stage, later veliger stage, and juvenile stage are distinct larval stages in B. areolata development. In this study, we used label-free quantification proteomics analysis of the three developmental stages of B. areolata. We identified a total of 5,583 proteins, of which 1,419 proteins expression level showed significant differential expression. The results of gene ontology enrichment analysis showed that the number of proteins involved in metabolic and cellular processes were the most abundant. Those proteins mostly had functions such as binding, catalytic activity and transporter activity. The results of Kyoto Encyclopedia of Genes and Genomes enrichment analysis showed that the number of proteins involved in the ribosome, carbon metabolism, and lysosome pathways were the most abundant, indicating that protein synthesis and the immune response were active during the three stages of development. This is the first study to use proteomics and real-time PCR to study the early developmental stages of B. areolata , which could provide relevant data on gastropod development. Our results provide insights into the novel aspects of protein function in shell formation, body torsion, changes in feeding habits, attachment and metamorphosis, immune-related activities in B. areolata larvae. [ABSTRACT FROM AUTHOR]