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Broodstock rearing is fundamental to produce high-quality offspring for aquaculture. However, reproduction requires large amounts of energy and nutrients, and physiological activities of digestive enzymes determine the absorption of energy and nutrients. However, the interaction between reproduction and digestive physiology is still unclear in sea cucumbers. In this study, we used laboratory experiments and field investigations to assess the variations of digestive physiology and digestive function in the sea cucumber Apostichopus japonicus during reproduction. Unexpectedly, activities of both amylase and trypsin were depressed in adult sea cucumbers during reproduction under both laboratory and field conditions. As a physiological consequence, digestive efficiencies of energy and organic matter decreased significantly during reproduction. Although reproductive output of sea cucumbers varied greatly between laboratory and wild conditions, reproductive effort had no effect on the activities of numerous digestive enzymes. Together, these data indicated that reproductive status induced digestive function decline in A. japonicus. Our study provided very important information about the reproductive biology of sea cucumbers that could be applied to broodstock rearing and conservation of this commercially important species. [ABSTRACT FROM AUTHOR]

The sea cucumber Apostichopus japonicus has important nutritional and medicinal value. Unfortunately, we know little of the source of active chemicals in this animal, but the plentiful pigments of these animals are thought to function in intriguing ways for translation into clinical and food chemistry usage. Here, we found key cell groups with the gene activity predicted for the color morphology of sea cucumber body using single-cell RNA-seq. We refer to these cell populations as melanocytes and quinocytes, which are responsible for the synthesis of melanin and quinone pigments, respectively. We integrated analysis of pigment biochemistry with the transcript profiles to illuminate the molecular mechanisms regulating distinct pigment formation in echinoderms. In concert with the correlated pigment analysis from each color morph, this study expands our understanding of medically important pigment production, as well as the genetic mechanisms for color morphs, and provides deep datasets for exploring advancements in the fields of bioactives and nutraceuticals. [ABSTRACT FROM AUTHOR]

Sea cucumber is a morphologically diverse and ecologically important clade of echinoderms. The sea cucumber Apostichopus japonicus is the most economically valuable species of sea cucumber. The initial assembly of the A. japonicus genome was released in 2017. However, this genome assembly is fragmented and lacks relative position information of genes on chromosomes. In this study, we produced a high-quality chromosome-level genome of A. japonicus using Pacbio HiFi long-reads and Hi-C sequencing data. The assembled A. japonicus genome spanned 671.60 Mb with a contig N50 size of 17.20 Mb and scaffold N50 size of 29.65 Mb. A total of 99.9% of the assembly was anchored to 23 chromosomes. In total, 19,828 genes were annotated, and 97.2% of BUSCO genes were fully represented. This high-quality genome of A. japonicus will not only aid in the development of sustainable aquaculture practices, but also lay a foundation for a deeper understanding of their genetic makeup, evolutionary history, and ecological adaptation. [ABSTRACT FROM AUTHOR]

Simple Summary: The sea cucumber Apostichopus japonicus is an important aquatic invertebrate in the aquaculture industry. It has high nutritional and medicinal value and is popular with consumers, in particular in Asia. The high demand for the species has led to declines in wild populations and A. japonicus is listed as an endangered species by IUCN. Aquaculture of sea cucumber is important to safeguard the conservation of the species in the wild, and its successful reproduction in captivity is a prerequisite for industrial production. It is known that parental nutrient reserves, in particular of lipids, are directly related to the reproductive performance of sea cucumbers. In this study, we investigated the impact of a high-fat diet on the intestinal and gonadal metabolism of male and female A. japonicus. Diet lipid content significantly affected the intestinal microbiome and metabolite profile, and also interfered with gonadal metabolites. Dietary lipid supplementation enhanced the dominance of Proteobacteria in the intestines. Other microbes in the intestines responded to a high-fat diet, which may contribute to maintain intestinal homeostasis. The physiological and metabolic responses of sea cucumbers to a high-fat diet showed sex differences. Interestingly, a correlation between intestinal and gonadal tissue levels of polyunsaturated fatty acid was found. The results of this study indicate that the lipid content in diets can be differentially adjusted for male and female sea cucumbers to improve nutrition and promote reproduction. This data also contributes to a better understanding of the reproductive biology and sex differences of sea cucumbers. Parental nutrient reserves are directly related to reproductive performance in sea cucumbers. This study focused on the lipid requirements of male and female sea cucumbers Apostichopus japonicus during the reproductive stage and analyzed their physiological responses to a high-fat diet (HFD). The intestinal lipid metabolites and microbiome profile changed significantly in animals fed with the HFD, as given by an upregulation of metabolites related to lipid metabolism and an increase in the predominance of Proteobacteria in the microbiome, respectively. The metabolic responses of male and female sea cucumbers to the HFD differed, which in turn could have triggered sex-related differences in the intestinal microbiome. These results suggest that the lipid content in diets can be differentially adjusted for male and female sea cucumbers to improve nutrition and promote reproduction. This data contributes to a better understanding of the reproductive biology and sex differences of sea cucumbers. [ABSTRACT FROM AUTHOR]

Sea cucumbers are economical and ecologically important species, playing a crucial role in nutrient recycling in the ocean and providing valuable bioactive compounds for nutrition. Previous research has demonstrated that microplastic fibers, which are widely recognized as emerging contaminants, are transferred to the perivisceral coelomic fluid during respiration in sea cucumbers; however, their fate in sea cucumbers is still not well understood. We tracked the status of sea cucumbers (Apostichopus japonicus) with polyester microplastic fibers in their coelomic fluid in clean water. The results showed that after transferring sea cucumbers to clean water, the number of microplastic fibers transferred significantly decreased in the coelomic fluid, but at least one microplastic fiber was found up to 60 days. In addition, sea cucumbers recovered from the effect of microplastic fiber transfer, as indicated by enzyme levels and histological observations. Furthermore, single microplastic fiber transfer over a 60‐day farmed period did not significantly affect the growth of sea cucumbers. However, repetitive microplastic fiber transfer (i.e., twice and thrice a week over 60 days) significantly decreased the growth rate (p < 0.05). Accordingly, increasing microplastic fibers in sea cucumber habitats pose a threat to sea cucumbers because they can disrupt development. Thus, farmers are advised to select locations for farming sea cucumbers where low microplastic fiber concentrations are expected. Environ Toxicol Chem 2023;42:205–212. © 2022 SETAC [ABSTRACT FROM AUTHOR]

Simple Summary: The sea cucumber Apostichopus japonicus is an ecologically significant echinoderm with considerable nutritional and therapeutic value. Color variation of A. japonicus is one of its most important cultivation traits, as color affects its bioactive compounds, taste, and market price. Microphthalmia-associated transcription factor (MITF) is one of the most critical genes in melanocyte development and melanin synthesis pathways. However, how MITF regulates body color and differentiation in sea cucumbers is poorly understood. Here, we analyzed the expression level and location of MITF in white, purple, and green sea cucumbers and identified the genes regulated by MITF using chromatin immunoprecipitation followed by sequencing. Our findings suggested that MITF contributed to the body color differentiation of green, purple, and white sea cucumbers A. japonicus through expression differences and regulation of downstream genes. These findings give researchers a foundation for further research into the processes that underlie the development of body color in sea cucumbers and provide light on how genes are regulated. The results will also provide support for sea cucumber breeding and a useful theoretical basis in order to contribute to the development of the sea cucumber industry. Melanin, which is a pigment produced in melanocytes, is an important contributor to sea cucumber body color. MITF is one of the most critical genes in melanocyte development and melanin synthesis pathways. However, how MITF regulates body color and differentiation in sea cucumbers is poorly understood. In this study, we analyzed the expression level and location of MITF in white, purple, and green sea cucumbers and identified the genes regulated by MITF using chromatin immunoprecipitation followed by sequencing. The mRNA and protein expression levels of MITF were all highest in purple morphs and lowest in white morphs. In situ hybridization indicated that MITF mRNA were mainly expressed in the epidermis. We also identified 984, 732, and 1191 peaks of MITF binding in green, purple, and white sea cucumbers, which were associated with 727, 557, and 887 genes, respectively. Our findings suggested that MITF contributed to the body color differentiation of green, purple, and white sea cucumbers through expression differences and regulation of downstream genes. These results provided a basis for future studies to determine the mechanisms underlying body color formation and provided insights into gene regulation in sea cucumbers. [ABSTRACT FROM AUTHOR]

Seed production plays an important role in aquaculture. The sea cucumber Apostichopus japonicus is an important marine aquaculture species in many Asian countries. By 2020, the annual total seed production of A. japonicus reached 551 billion individuals in China. However, the traditional method of culturing A. japonicus larvae is cost intensive and causes environmental pollution. In this study, we developed an eco‐friendly method for rearing sea cucumber larvae. We designed a cage system to provide a suitable living environment for larvae in open‐air outdoor ponds, and then, we identified 0.2 larvae per ml as the optimal stocking density for larval rearing. We also found that substrates made of oyster and scallop shells were optimal for larval settlement. A. japonicus larvae showed good survival, growth, development and settlement when cultured using this low‐cost and non‐polluting method. Our results can be applied to support sustainable development of the sea cucumber industry. [ABSTRACT FROM AUTHOR]

Neuropeptides are endogenous active substances that are present in nervous tissues and participate in behavioral and physiological processes of the animal system. Locomotor behavior is basic to predation, escape, reproduction in animals, and neuropeptides play an important role in locomotion. In this study, the function of pedal peptide-type neuropeptide (PDP) in the process of locomotor behavior of the sea cucumber Apostichopus japonicus was evaluated. The locomotor behavior of A. japonicus was recorded by infrared camera before and after PDP administration, and muscle physiology was studied by ultra performance liquid chromatography and quadrupole time-off-light mass spectrometry (UPLC-Q-TOF-MS) to clarify the potential physiological mechanisms. The results showed that PDP enhanced the cumulative duration of moving significantly at the 7th h after injection, and reduced the mean and maximum velocity by 16.90 and 14.22% in A. japonicus. The data of muscle metabolomics suggested that some significantly changed metabolites were related to locomotor behavior of sea cucumbers. The decreases of phosphatidylethanolamine (PE) and phosphatidylcholine (PC) might result in the increases of lysophosphatidylcholines (lysoPC) and lysophosphatidylethanolamine (lysoPE), and suggested the change of fluidity and permeability in the muscle cell membrane, which would affect the physiology and function of muscle cells, and finally alter the locomotor behavior. In addition, the increased level of arachidonic acid (ARA) might activate K+ ion channels and then affect the signaling of muscle cells, or promote the sensitivity of muscle cells to Ca2+ and then result in the contractility of longitudinal muscles in sea cucumbers. ARA was also involved in the linoleic acid metabolism which was the only pathway that disturbed significantly after PDP administration. In conclusion, PDP participated in the regulation of locomotor behavior in the sea cucumber, and the decreased PE and PC, increased lysoPC, lysoPE and ARA might be the potential physiological mechanisms that responsible for behavioral effects of PDP in A. japonicus. [ABSTRACT FROM AUTHOR]

Physiological plasticity allows animals to adjust their physiological function to abiotic and biotic variations. It has been mostly studied in the context of response to external factors and not much is known on how animals adjust their physiology to cope with variations in internal conditions. The process of reproduction implies gonadal maturation and other internal changes, bringing various challenges to the animal such as an increased demand for energy and oxygen. Here, the capacity of the sea cucumber, Apostichopus japonicus to adjust its respiratory function and physiological mechanisms during reproduction was studied using a time-lapse videography and metabolomics approach. The results showed that reproduction caused a significant increase in oxygen consumption in A. japonicus. Interestingly, breeding sea cucumbers can accommodate the high oxygen demand by accelerating respiratory rate. However, to maintain a necessary high level of respiratory activity during reproduction, sea cucumbers need consume large amounts of adenosine triphosphate (ATP). In addition, the metabolomic data suggests that oxidative stress and hormone regulation are the physiological mechanisms linking reproduction and respiratory function. Altogether, these findings suggest that plasticity of respiratory function is an effective tactic to cope with high oxygen demand during reproduction. [ABSTRACT FROM AUTHOR]

In this study, we evaluated the behavioural characteristics of the epithelial tissues of sea cucumber (Apostichopus japonicus) subjected to illumination. The behavioural results indicated that the tentacles, tube feet, and spines were sensitive to light with structural changes. Among the three epithelial tissues, the tentacles were the most sensitive with the shortest reaction and recovery times, whereas the tube feet and spines had longer reaction times. Quantitative real-time PCR (q-PCR) was used to analyse the changes of Pax6 expressions before and after illumination in the tentacles, tube feet and spines. Q-PCR results indicated that Pax6 expressions in the three above tissues after illumination were higher than that before illumination. We hypothesised that sea cucumber may not have independent photoreceptors, but the epithelial tissues were capable of exhibiting a behavioural response to light. This will allow us to re-examine the functions of all epithelial tissues of sea cucumbers. [ABSTRACT FROM AUTHOR]

The mass mortalities of sea cucumber Apostichpous japonicus have prevailed in northern China, mainly attributing to the emergence of extreme environmental conditions, that is hyperthermia and hyposalinity. The high‐quality sea cucumber seedlings appear to possess more robust resistance to adverse conditions. There are usually indoor‐ and outdoor‐cultured seedlings in industrial production of sea cucumbers. Although the outdoor‐cultured sea cucumbers are practically considered to be more strong and robust, the effective evaluation approach to distinguish these seedlings has been scarce. The current study compared survival and immune performances of indoor‐ and outdoor‐cultured A. japonicus under combined exogenous stressors, that is hyperthermia and hyposalinity. Results based on secondary stress induction revealed that the activities of immune enzymes and levels of catecholamines in body wall of outdoor‐cultured seedlings were prominently higher than those of indoor‐cultured seedlings recovered for 0–72 hr following sublethal stress (30°C and 25 psu of salinity). The opposite case occurred on immune enzymes in coelomic fluid of the two sources of seedlings except for myeloperoxidase. Importantly, the outdoor‐cultured seedlings, which were recovered for 72 hr after sublethal stress, exhibited a 93% of cumulative survival rate following 7 days of recovery after lethal stress (33°C and 20 psu of salinity), 27% higher than the indoor‐cultured seedlings. Collectively, the outdoor‐cultured A. japonicus seedlings showed more superior quality than the hatchery‐produced seedlings in terms of survival and immune performance. These findings provide practically useful information towards quality distinction of the indoor‐ and outdoor‐cultured sea cucumbers, which could benefit the aquaculture industry to obtain high‐quality seedlings. [ABSTRACT FROM AUTHOR]

Sea cucumbers are free of protective exoskeleton and capable of autolysis under stress conditions. The live transport of small‐size juveniles to grown‐out sites induces hypoxia and congesting stress. The transport process is essential to production of outdoor healthy seedlings. Here, we evaluated the effects of damp transport and water transport on Apostichopus japonicus, an economic species inhabiting along the Asian coast. The survival after transport and immune performance of small‐size juveniles (0.05–0.1 g of immersed weight) were monitored during distinct duration of transport (1, 3, 5, 8 and 12 hr). The results revealed that there were no significant differences between the two transport systems within 5 hr. Given the survival for recovery of 48 hr and responses of immune enzymes and catecholamines during transport, water transport was less detrimental to sea cucumbers than damp transport when the transport duration was less than 8 hr. Once the duration prolonged to 12 hr, these immune parameters changed irregularly and the survival declined drastically. Water transport with a notably higher survival for juveniles was the more appropriate manner for long‐time transport. These findings provide insights into long‐term transport of small‐size A.  japonicus juveniles and might be beneficial for production of ecologically healthy seedlings. [ABSTRACT FROM AUTHOR]

The concentrations of eight heavy metals (As, Cd, Cr, Cu, Mn, Ni, Pb and Zn) were measured in the sediment, the isolated microplastics from the sediment and the body wall of sea cucumbers from farms in China. Accordingly, the heavy metal concentrations in the sediment were below the class I upper limit of Chinese sediment quality guidelines. Among heavy metals, the median concentrations of Cd and As were higher in the body wall than in the corresponding sediment. Additionally, the median concentrations of Cd, Pb, and Zn were higher on the microplastics than in the corresponding sediment. Furthermore, there was no significant correlation among heavy metals in sediment, sea cucumber and microplastics. This study contributes to the understanding of the heavy metal accumulation in the sediment, the microplastics and the body wall of the sea cucumber. Unlabelled Image • Microplastics may serve as a vector of heavy metals in the sea cucumber farms. • Sea cucumber may have a strategy accumulating some heavy metals in the body wall. • Sea cucumber A. japonicus might be considered as a bio-monitor for Cd. [ABSTRACT FROM AUTHOR]

The sea cucumber Apostichopus japonicus (Selenka) is a valuable economic species in Southeast Asia. It has many fascinating behavioral characteristics, such as autolysis, aestivation, regeneration, and evisceration, thus it is a notable species for studies of special behaviors. Evisceration and autotomy are controlled by the neural network and involve a complicated physiological process. The occurrence of evisceration behavior in sea cucumbers is strongly related to their environment, and it negatively impacts their economic value. Evisceration behavior plays a pivotal role in the survival of A. japonicus , and when it is induced by dramatic changes in the coastal ecological environment and the aquaculture setting it can strongly affect the economic performance of this species. Although numerous studies have focused on intestinal regeneration of A. japonicus , less is known about evisceration behavior, especially its underlying molecular mechanisms. Thus, identification of genes that regulate evisceration in the sea cucumber likely will provide a scientific explanation for this significant specific behavior. In this study, Illumina sequencing (RNA-Seq) was performed on A. japonicus specimens in three states: normal (TCQ), eviscerating (TCZ), and 3 h after evisceration (TCH). In total, 129,905 unigenes were generated with an N50 length of 2651 base pairs, and 54,787 unigenes were annotated from seven functional databases (KEGG, KOG, GO, NR, NT, Interpro, and Swiss-Prot). Additionally, 190, 191, and 320 genes were identified as differentially expressed genes (DEGs) in the comparisons of TCQ vs. TCZ, TCZ vs. TCH, and TCQ vs. TCH, respectively. These DEGs mapped to 157, 113, and 190 signaling pathways in the KEGG database, respectively. KEGG analyses also revealed that potential DEGs enriched in the categories of "environmental information processing," "organismal system," "metabolism," and "cellular processes," and they were involved in evisceration behavior in A. japonicus. These DEGs are related to muscle contraction, hormone and neurotransmitter secretion, nerve and muscle damage, energy support, cellular stress, and apoptosis. In conclusion, through our comparative analysis of A. japonicus in different stages, we identified many candidate evisceration-related genes and signaling pathways that likely are involved in evisceration behavior. These results should help further elucidate the mechanisms underlying evisceration behavior in sea cucumbers. Figure above is the hierarchical clustering of DEGs in three comparison groups of evisceration behavior (TCQ-vs-TCZ, TCZ-vs-TCH and TCQ-vs-TCH) in A. japonicus. This figure reveals the overall up- and downregulation of differentially expressed genes (DEGs) that involved in the evisceration behavior of sea cucumber A. japonicus. These DEGs fell into the categories of "stimuli response", "signal transduction", "organismal system", and "metabolism", and are suggested that muscle contraction, hormone and neurotransmitter secretion, nerve and muscle damage, energy support, cellular stress and apoptotic are involved in the evisceration behavior in A. japonicus. Unlabelled Image [ABSTRACT FROM AUTHOR]

Host-intestine microbiota interactions have been widely studied in aquatic animals, but these interactions in the intestine regeneration process of the sea cucumber Apostichopus japonicus have been rarely investigated. To understand how intestine regeneration impacts the developing intestinal microbiome composition and function, we performed a case study to characterize the intestinal microbial composition and functional genes of A. japonicus during intestine regeneration stages. High-throughput 16S rRNA gene sequencing revealed significantly different intestine microbiota compositions in different regeneration stages. The phylogenetic diversity and composition of the intestinal microbiota changed significantly in the early regeneration stage and tended to recover in the end stage. During the regeneration process, the abundance of Bacteroidetes and Rhodobacterales increased significantly. A network analysis revealed that Rhodobacteraceae and Flavobacteriaceae may function as keystone taxa in the intestinal microbial community of A. japonicus during intestine regeneration. Metagenomic analyses of representative samples revealed that the microbiomes of regenerating intestines were enriched in genes facilitating cell proliferation, digestion and immunity. The increased abundance of Bacteroidetes elevated the enrichment of genes associated with carbohydrate utilization. Some functional features in the subsystem category changed in a pattern that was consistent with the changing pattern of microbiota composition during intestine regeneration. Our results revealed that seemingly regular alterations in the intestinal microbiome composition and function are associated with intestine regeneration stages. Intestinal microbiota can increase the abundance of beneficial bacterial members and upregulate related functional genes to adapt to intestine regeneration and reconstruct a stable community structure. This study provides a new insight into the mechanism of the host-microbiota interaction response to organ regeneration. [ABSTRACT FROM AUTHOR]

Melatonin is a highly conserved hormone in evolutionary history. It occurs in numerous organisms and plays a role in the endocrine and immune systems. Locomotor behavior is a basic behavior in animals and is an important indicator of circadian rhythms, which are coordinated by the nervous and endocrine systems. To date, the effect of melatonin on locomotor behavior has been studied in vertebrates, including syrian hamsters, sparrows, rats, zebrafish, goldfish, and flatworms. However, there have been few studies of the effects of melatonin on locomotor behavior in marine invertebrates. The goals of present study were to show the existence of melatonin in the sea cucumber Apostichopus japonicus and to evaluate its effect on locomotor activity. In addition, muscle tissues from control and melatonin-treated sea cucumbers were tested using ultra performance liquid chromatography and quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) to determine the changes of metabolic activity in muscle. Melatonin was present in the coelomic fluid of A. japonicus at a concentration of ∼135.0 ng/L. The total distance traveled and number steps taken over 9 h after melatonin administration decreased with increasing concentration of the melatonin dose. Mean and maximum velocity of movement and stride length and stride frequency also decreased, but their differences were not statistically significant. Overall, these results suggest that melatonin administration had a sedative effect on A. japonicus. The levels of 22 different metabolites were altered in the muscle tissues of melatonin-treated sea cucumbers. Serotonin, 9- cis retinoic acid, all-trans retinoic acid, flavin mononucleotide in muscles were downregulated after melatonin administration. Moreover, a high free fatty acid (FFA) concentration and a decrease in the adenosine 5′-triphosphate (ATP) concentration in the muscle tissues of the melatonin-treated group were detected as well. These results suggest that the sedative effect of melatonin involves some other metabolic pathways, and the reduced locomotor modulator—serotonin, inhibited fatty acid oxidation and disturbed oxidative phosphorylation are potential physiological mechanisms that result in the inhibitory effect of melatonin on locomotion in sea cucumbers. [ABSTRACT FROM AUTHOR]

Abstract Microplastic ingestion by the farmed sea cucumber is undocumented. Microplastics were isolated from the sea cucumber Apostichopus japonicus that was collected from eight farms along the Bohai Sea and the Yellow Sea in China. To examine microplastic ingestion, the intestines were isolated, digested and then subjected to the floatation test. The microplastic abundance in the sediment ranged from 20 to 1040 particles kg−1 of dry sediment, while the ingested microplastics ranged from 0 to 30 particles intestine−1. After filtering the coelomic fluid, the extracted microplastics from the coelomic fluid ranged from 0 to 19 particles animal−1. Thus, we speculated that microplastics may transfer to the coelomic fluid of sea cucumber. The ingested microplastics did not correlate with the animal body weight but was site dependent, suggesting that sea cucumber may serve as sentinel for microplastic pollution monitoring in the sediment. The microplastics were identified by Fourier transform infrared micro spectroscopy, and the polymer types were mainly cellophane, polyester, and polyethylene terephthalate. This study revealed that, microplastics widely existed in sea cucumber farms, and that sea cucumbers ingest microplastics as suitable with their mouth open. Moreover, the microplastics might transfer to the coelomic fluid of the sea cucumber. Further investigations are needed to assess the chronic effect of the microplastics on the growth and physiological status of the sea cucumber. Graphical abstract Image 1 Highlights • The farmed sea cucumber ingested microplastics with an average of 10 MP per intestine. • Microfibres were predominantly detected from the habitat of sea cucumber. • Microplastic might transfer to the coelomic fluid of sea cucumber. • A. japonicus can serve as sentinels for microplastic pollution in the sediments. The farmed sea cucumber Apostichopus japonicus ingests microplastics as suitable with their mouth open, and these microplastics might transfer to the coelomic fluid of the sea cucumber. [ABSTRACT FROM AUTHOR]

Abstract Economically important marine organisms face severe environmental challenges, such as high temperature and low dissolved oxygen, from global climate change. Adverse environmental factors impact the survival and growth of economically important marine organisms, thereby negatively influencing the aquaculture industry. However, little is known about the responses of sea cucumbers to combined environmental co-stressors till now. In this study, ultra-performance liquid chromatography (UPLC) was utilized to obtain metabolic profiles of sea cucumbers. Changes in the concentrations of 84, 68, and 417 metabolites related to the responses of sea cucumbers to heat (26 °C), hypoxia (2 mg/L) and the combined stress, respectively, were observed and analyzed. Representative biomarkers were discussed in detail, including deltaline, fusarin C, halichondrin B and rapanone. The concentration of metabolites involved in the regulation of energy metabolism, including amino acid, carbohydrate and lipid metabolism were significantly changed, and the tricarboxylic acid (TCA)-cycle was significantly altered under heat plus hypoxia. We interpreted these changes partly as an adaptation mechanism in response to environmental stress. Based on the decreased accumulation of glutamine, we hypothesized that heat stress is the main factor that interferes with the process of glutamic acid-glutamine metabolism. The present study showed that combined environmental stressors have a more extensive impact on the metabolites of the respiratory tree in sea cucumbers than single stress. These results would facilitate further development of the sea cucumber as an echinoderm model to study mechanisms of response to adverse environments, as well as to help advance knowledge of the adaptation of marine organisms to global climate change. Highlights • UPLC was utilized to obtain metabolic profiles of sea cucumbers under heat, hypoxia and the combined stress. • Synergistic effect of environmental stressors has an additive impact on the primary metabolome in sea cucumbers. • Ten representative potential biomarkers of heat and hypoxia in sea cucumber are illustrated. • The levels of metabolites involved in the regulation of energy metabolism were significantly changed. • The tricarboxylic acid (TCA)-cycle was significantly altered under the combined stress of heat and hypoxia. [ABSTRACT FROM AUTHOR]

Abstract Pigmentation processes provide a traceable and relevant trait for understanding key issues in evolutionary biology such as adaptation, speciation and the maintenance of balanced polymorphisms. The sea cucumber Apostichopus japonicus , which has nutritive and medical properties, is considered the most valuable commercial species in many parts of Asia. Compared with the green morph, the purple morph is rare and has great appeal to consumers. However, little is currently known about the molecular mechanism of body color formation in A. japonicus , even in echinoderm. Here, we employ illumina sequencing to examine expression patterns of the gene network underlying body wall development in purple and green morphs of A. japonicus. Overall, the number of down-regulated genes in the green morph was significantly more than in the purple morph during the pigmentation stage. We observed dynamic expression patterns of a large number of pigment, regulation and growth genes from the "Melanogenesis", "Melanoma", "Wnt signaling pathway", "Notch signaling pathway", "epithelium development", "epidermal growth factor receptor binding","growth factor activity" and "growth", including contrasting expression patterns of these genes in green and purple morph. This study provides comprehensive lists of differentially expressed genes during body wall development in the green and purple morphs, revealing potential candidate genes that may be involved in regulating body color formation and polymorphism. These data will provide valuable information for future genetic studies on sea cucumbers elucidating the molecular mechanisms underlying pigmentation, and may support the culture of desirable color morphs. [ABSTRACT FROM AUTHOR]

The sea cucumber Apostichopus japonicus is a deposit-feeder and vital for marine benthic ecosystems. Hypoxia can influence the behaviour and even lead to massive mortality in A. japonicus in the wild. It is important to understand the molecular responses of A. japonicus when exposed to acute changes in dissolved oxygen (DO) concentration. In this study, RNA-seq provided a general overview of the gene expression profiles of the respiratory tree of A. japonicus exposed to DO of 8 mg l−1 (DO8), 4 mg l−1 (DO4) and 2 mg l−1 (DO2) conditions. Differentially expressed genes (DEGs) screening with the NOISeq method identified 51, 59 and 61 DEGs according to the criteria of fold change ≥2 and divergence probability ≥0.8 in the comparisons of DO2 vs DO4, DO2 vs DO8 and DO4 vs DO8, respectively. Gene ontology analysis showed that 'cellular process' and 'binding' had the most enriched DEGs in the categories of 'biological process' and 'molecular function', respectively (catalytic activity also had the most enriched DEGs in the category of 'molecular function' based on the comparison of DO2 vs DO8), while 'cell' and 'cell part' had the most enriched DEGs in the category of 'cellular component'. The DEGs were mapped to 79, 81 and 104 pathways in the KEGG database, and 8, 29 and 16 pathways were significantly enriched, respectively. The DO-specific DEGs identified in this study of the respiratory tree are important targets for further research into the biochemical mechanisms involved in the response of the sea cucumber to changes in the DO concentration. [ABSTRACT FROM AUTHOR]

Sea cucumbers exposed to stressful circumstances eviscerate most internal organs, and then regenerate them rapidly under favorable environments. Reversible protein phosphorylation and acetylation are major modifications regulating protein function. Herein, for the first time, we perform quantitative phospho- and acetyl proteomics analyses of intestine regeneration in a sea cucumber species Apostichopus japonicus. We identified 1,862 phosphorylation sites in 1,169 proteins, and 712 acetylation sites in 470 proteins. Of the 147 and 251 proteins differentially modified by phosphorylation and acetylation, respectively, most were related to cytoskeleton biogenesis, protein synthesis and modification, signal recognition and transduction, energy production and conversion, or substance transport and metabolism. Phosphorylation appears to play a more important role in signal recognition and transduction than acetylation, while acetylation is of greater importance in posttranslational modification, protein turnover, chaperones; energy production and conversion; amino acid and lipid transport and metabolism. These results expanded our understanding of the regulatory mechanisms of posttranslational modifications in intestine regeneration of sea cucumbers after evisceration. [ABSTRACT FROM AUTHOR]

Abstract: As an intertidal species, Apostichopus japonicus is subject to diel and seasonal temperature fluctuations. Color variation is a distinct characteristic of A. japonicus, and a new color morph, purple A. japonicus, was recently found on the coast of Rushan, Weihai City. This study was conducted to compare the performance of green, white, and purple color morphs of A. japonicus at different water temperatures to help improving aquaculture technology and management. In this study, green, white, and purple color morphs of juvenile A. japonicus (1.5 ± 0.1 g) were cultured at 10, 14, 18, 22, and 26 C for 60 d, according to the suitable temperature range for sea cucumber growth. Temperature was shown to have a significant effect on growth, energy budget, and physiology of sea cucumbers (P < 0.05). Specific growth rates, feed conversion efficiencies, and the proportion of energy allocated to growth of all three color morphs were optimal at 18 C. Activities of the enzymes related with oxidative stress, immune response, and digestion were determined. Superoxide dismutase (SOD) and trypsin activities generally reached a maximum in all three color morphs at 18 C. The purple color morph of A. japonicus was higher in growth rate, food conversion efficiency, and proportion of energy allocated to growth than green and white color morphs at 18 and 22 C, consistent with its higher trypsin and SOD activity, indicating the mutual effect of growth and physiology. At 18, 22, and 26 C, the green color morph had the highest level of lysozyme activity and purple color morph had the lowest, indicating possible infection by external pathogens of green color morph, which might be caused by high temperature. These results suggested that the optimum temperature for culture of the three color morphs was approximately 18 C, the purple had a better adaption to high temperature, and the green and white color morphs may be more susceptible to thermal stress than the purple color morph. [ABSTRACT FROM AUTHOR]

Abstract: Two groups of Apostichopus japonicus, a thermotolerant strain (group G3: wet weight, 64.22 ± 13.16 g/ind.), which was selected focusing on the performance of thermo‐tolerance through three generations for 10 years, and a control group (group C: wet weight, 62.08 ± 12.01 g/ind.) were collected from July to October in a seawater pond in northern China. Differences in relative faecal mass (RFM), relative intestinal mass (RIM), percentage of individuals with faeces (PIWF) and intestinal metabolites were investigated and compared between the two groups. The temperatures of terminating aestivation of the two groups were assessed according to the values of RFM and RIM. A regression analysis showed that the corresponding group G3 temperatures were 0.56–1.34°C and 0.70–1.49°C higher than those of group C when RFM and RIM were 0.01–0.05 and 0.005–0.025 respectively. The PIWF values in group G3 were 11.5%–21.2% higher than that in group C from 20 July to 22 September. Significant differences at the concentrations of 52 metabolites were detected between the two groups, 36 were higher in group G3 and 16 were higher in group C. The concentrations of threitol, 2‐methylglutaric acid, N‐acetyl‐D‐galactosamine, N‐acetyl‐L‐leucine, lactose, oxoproline, 2,3‐dimethylsuccinic acid and d‐glucoheptose were significantly different between groups G3 and C and were considered metabolic markers distinguishing group G3 from group C. Metabolism of A. japonicus in group G3 was more active than that in group C. These results provide new insight for understanding ingestion and intestinal metabolism in the thermotolerant strain of A. japonicus under high summer temperature. [ABSTRACT FROM AUTHOR]

Sea cucumber , Apostichopus japonicus is an important species for aquaculture, and its behavior and physiology can change in response to changing salinity conditions. For this reason, it is important to understand the molecular responses of A. japonicus when exposed to ambient changes in salinity. In this study, RNA-Seq provided a general overview of the gene expression profiles in the intestine of A. japonicus exposed to high salinity (SD40), normal salinity (SD30) and low salinity (SD20) environments. Screening for differentially expressed genes (DEGs) using the NOISeq method identified 109, 100, and 89 DEGs based on a fold change of ≥ 2 and divergence probability ≥ 0.8 according to the comparisons of SD20 vs. SD30, SD20 vs.SD40, and SD30 vs. SD40, respectively. Gene ontology analysis showed that the terms “metabolic process” and “catalytic activity” comprised the most enriched DEGs. These fell into the categories of “biological process” and “molecular function”. While “cell” and “cell part” had the most enriched DEGs in the category of “cellular component”. With these DEGs mapping to 2119, 159, and 160 pathways in the Kyoto Encyclopedia of Genes and Genomes database. Of these 51, 2, and 57 pathways were significantly enriched, respectively. The osmosis-specific DEGs identified in this study of A. japonicus will be important targets for further studies to understand the biochemical mechanisms involved with the adaption of sea cucumbers to changes in salinity. [ABSTRACT FROM AUTHOR]

Abstract: We evaluated the effects of different proportions of dietary protein (5%, 10%, 15%, 20%, 25% and 30% protein) on the activity of digestive enzymes of normal and albino Apostichopus japonicus. The experimental diets were fed for 60 days, the optimal conditions for digestive enzyme activity in sea cucumbers were studied. The optimal temperature for protease was 29.3°C and the optimal pH was 1.8. The optimal temperature for amylase was 34.3°C and the optimal pH was 6.7. The optimal temperature for cellulase was 56°C and the optimal pH was 5.9. The activity of intestinal protease increased at first and then decreased as the proportion of dietary protein increased, reaching the maximum when the proportion of protein was 19.7%. The activity of protease in the intestine of normal sea cucumber was significantly lower than that of albino sea cucumber, and the activity of amylase was significantly higher than that of albino sea cucumber. This study is expected to provide a basis for further explaining the ecological difference of albino and normal A. japonicus. [ABSTRACT FROM AUTHOR]

The body colour of sea cucumber, Apostichopus japonicus (Selenka), is an important trait affecting the price and taste of its products; the rare white and purple colour types are favoured and are more expensive in China. Identification of factors that may contribute to the differences among white, green and purple sea cucumbers will provide a scientific basis for improving the cultivability of the rare colour morphs. In this study, the growth, histology, ultrastructure and expression of microphthalmia-associated transcription factor ( MITF) and astacin of two newly discovered white and purple colour morphs were investigated and compared with the common green morph, in the same breeding environment. At 50 days old, the growth and survival rates and the extent of pigmentation were the highest in purple, then green colour morphs and were lowest in white morphs. The white morph had fewer, and less developed, epidermal melanocytes compared with the green and purple colour morphs. MITF and astacin expression, which are necessary for the formation of melanin and astaxanthin, respectively, were highest in purple morphs and lowest in white morphs. In addition, there were significant differences in growth rates and expression of MITF and astacin among early, mid and late pigmentation stages of each colour morph. The results suggested that growth and survival rates were highest in purple sea cucumber and lowest in white sea cucumber. Epidermis thickness and melanin content may be the newfound factors contributed to the differences in growth and survival rate among three colour morphs. [ABSTRACT FROM AUTHOR]

The sea cucumber Apostichopus japonicus is an economic species mainly distributed along the coast of northern China, south-eastern Russia, Japan, Republic of Korea and Democratic People's Republic of Korea. Aquaculture industry of A. japonicus has been facing severe challenge of high temperature. In this study, we studied the mRNA expression profiles of eight key metabolic enzymes involved in carbohydrate and amino acids metabolism in A. japonicus under heat stress. The expression of hexokinase, pyruvate kinase and malate dehydrogenase showed downregulated response to heat stress, while the expression of glutamate dehydrogenase, alanine transaminase and branched-chain aminotransferase showed upregulated response. In addition, the expression of lactate dehydrogenase and glutamate synthase showed no significant difference. We also applied 1H NMR-based metabolomics to investigate metabolic changes in the intestine tissue of A. japonicus under heat stress, the results of which revealed nine increased and 10 decreased metabolites in the heat stress group. These response genes and metabolites have potential to become markers for identifying severity of heat stress. More importantly, our findings suggest significant links between gene expression and metabolites changing, highlighting regulation networks of carbohydrate and amino acid metabolism in heat-stressed A. japonicus. [ABSTRACT FROM AUTHOR]

Low dissolved oxygen (LO) in seawater negatively affects aquatic animals and has received considerable attention. However, there is still much to learn about how echinoderms, which are keystone species in benthic ecosystems, respond to hypoxic stress. Here, we detected differentially expressed metabolites (DEMs) in sea cucumber (Apositchopus japonicus) between normoxic conditions (NC group) and hypoxic conditions (2 mg L−1) for 3 and 7 days (i.e., LO3 and LO7 groups). A total of 243, 298, and 178 DEMs were found in the NC versus LO3, NC vs. LO7, and LO3 vs. LO7 comparisons, respectively. Amino acids were the most abundant class of DEMs, and "biosynthesis of amino acids" was an enriched pathway in all three comparisons. Most of the enriched metabolite sets under hypoxic stress were related to metabolism. As the duration of the hypoxia treatment extended, the metabolism-related process maintained an upward trend, and signaling pathways maintained a downward trend. Thus, metabolism-related processes are affected in hypoxia-stressed sea cucumber, and amino acid metabolism is the most important process for adaption to hypoxic conditions, potentially function in osmotic regulation and energy regulation. Our results shed light on the adaptative strategies of sea cucumber to challenging environmental conditions. [Display omitted] • Changed metabolites in A. japonicus under hypoxic conditions were identified. • Biosynthesis of amino acids was the main pathway involved in the hypoxia response. • Prolonged hypoxia stimulated metabolism and depressed signaling pathways. • Amino acid metabolism is vital for adaptation of A. japonicus to hypoxic stress. [ABSTRACT FROM AUTHOR]

Determining the amount of microplastics (MPs) in food is key to clarifying their potential toxicity to humans. Here, we collected canned, instant, and salt-dried sea cucumbers Apostichopus japonicus , the most valued sea cucumbers, from Chinese markets to determine their content of MPs. Sea cucumbers contained MPs in the range of 0–4 MP individual−1, an average of 1.44 MP individual−1, and 0.081 MP g−1. Accordingly, consuming 3 g of sea cucumbers could result in an exposure risk of an average of 0.51 MPs, 0.135 MPs, and 0.078 MPs day-1 for canned, instant, and salt-dried sea cucumbers, respectively. MPs were in size range of 12–575 μm, and fibrous shape was dominant. Furthermore, among the five polymers identified, polypropylene showed the highest energy binding with two catalysts engaged in organic chemical oxidation. This study extends the knowledge regarding MPs occurrence in food and provides a theoretical basis for MPs toxicity in humans. [Display omitted] • Microplastics average in processed sea cucumbers was 1.44 MP individual−1. • The major size of microplastics was <100 μm. • Polyester was the dominant polymer identified in processed sea cucumbers. • Molecular docking showed that polypropylene has the highest potential toxicity. [ABSTRACT FROM AUTHOR]

Vibrations exist widely in the ocean, and the one caused by sound and biological movement plays an important role in the sensory system of marine organisms. The vibration caused by sound has many characteristics that make it a good candidate for modifying the movements of marine organisms. However, few studies have tested whether hydraulic vibration caused by sound has effects on the migration of sea cucumbers, and this has never been systematically studied previously in Apostichopus japonicus (Selenka). In order to understand whether hydraulic vibration caused by sound at different frequencies could affect the migration of sea cucumbers, in the present study, hydraulic vibration caused by sound at various frequencies was tested in the laboratory to determine their effects on the migration of A. japonicus at different sizes. The mean probability distribution was used as a statistical index to demonstrate the moving tendencies of the species. The experimental results showed that medium and small A. japonicus (<10 g ind.−1) tend to move towards the low-frequency vibration source caused by sound (100 Hz), whereas all sizes of A. japonicus tend to move backwards the high-frequency vibration source caused by sound (10 000 and 28 000 Hz). This study provides basic data on the behavioural ecology of this species, as well as theoretical reference for the design of artificial reefs and harvesting equipment for A. japonicus. [ABSTRACT FROM AUTHOR]