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As an important form of renewable energy, offshore wind power can effectively reduce dependence on traditional energy sources and decrease carbon emissions. However, operation of wind turbines can generate underwater noise that may have negative impacts on marine benthic organisms in the surrounding area. Sea cucumbers are slow-moving invertebrates that inhabit the ocean, relying on their immune system to adapt to their environment. To evaluate the frequency range of characteristic noise produced by offshore wind turbines, we conducted a field survey. Additionally, we utilized sea cucumbers in simulated experiments to assess their response to the noise produced by offshore wind turbines. We established a control group, a low-frequency noise group simulating offshore wind turbine noise at 125 Hz and 250 Hz, and a high-frequency noise group at 2500 Hz, each lasting for 7 days. Results from measuring immune enzyme activity in the coelomic fluid suggest that noise can reduce the activity of superoxide dismutase enzymes, which may make sea cucumbers more susceptible to oxidative damage caused by free radicals. Exposure to low-frequency noise can have the effect of diminishing the activity of catalase, and this decrease in catalase activity could potentially increase the susceptibility of the sea cucumber's coelom to inflammation. In order to elucidate the hypothetical mechanism of immune response, intestinal tissue was extracted for transcriptome sequencing. The results showed that under 125 Hz low-frequency noise stress, the number of differentially expressed genes was the highest, reaching 1764. Under noise stress, sea cucumber's cell apoptosis and cell motility are reduced, interfering with lipid metabolism process and membrane synthesis. This research provides theoretical support for the environmental safety assessment of offshore wind power construction., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Gender differences in physiological characteristics are widespread in animals. Herein, differentially expressed genes (DEGs) in gonads of the sea cucumber Apostichopus japonicus were analysed by transcriptomics, and the results showed that 19,973 genes were commonly expressed in the males and females, 4186 were female-biased, and 2540 were male-biased, 4695 genes were up-regulated in the females and 3436 genes were up-regulated in the males. These DEGs were mainly associated with metabolism, including lipid metabolism, amino acid metabolism, nucleotide metabolism, energy metabolism, and cofactor and vitamin metabolism. 29 Cytochrome P450 (CYP) superfamily genes with gender differential expression were selected, and performed gene identification, phylogenetic, and functional analyses. The results indicated significant roles in multiple metabolic pathways, such as steroid hormone biosynthesis, ovarian steroidogenesis, cortisol synthesis and secretion, arachidonic acid metabolism, linoleic acid metabolism, and retinol metabolism. The findings provide insight into the molecular characteristics of physiological gender differences in sea cucumbers, and will help lay the foundation for the establishment of effective sea cucumber breeding technologies., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Multiple environmental stressors caused by global warming influence the regulation of proteins involved in various biological processes in aquatic organisms. As an important component of the marine ecosystem, sea cucumber is a suitable echinoderm species for researching stress responses. In this study, we have investigated the proteomic response of respiratory trees in the sea cucumber Apostichopus japonicus, challenged with environmental stresses by using the iTRAQ technique. Results showed that 262, 155 and 433 proteins were differentially regulated in response to heat, hypoxia, and heat plus hypoxia, respectively. Expression of key genes and proteins were measured by real-time PCR and western blot to validate the accuracy of the proteome files. Results showed that the interaction between these two stressors has an additive effect at the proteome level. Proteins involved in amino acid and carbohydrate metabolic processes were largely induced by heat while repressed by hypoxia. Exposure to multiple climate change stressors caused several proteins involved in lipid metabolic progress to be down-regulated and lipid catabolic processes were induced. Additionally, hypoxia and the combined stress induced proteins involved in iron homeostasis. ATP synthesis and gluconeogenesis were induced under heat and the combined stress, while ATP and glycogen synthesis were depressed under hypoxia. Proteins related with immune and defense response were largely induced and protein synthesis ability was depressed under all three stresses. Thus, sea cucumber may adopt different strategies to cope with varied environmental stress, and the situation in heat group is more similar with the combined treatment than hypoxia group. These proteomic changes in response to high-temperature and low-oxygen levels may provide insights into the defense strategies of sea cucumber in response to global climate changes. SIGNIFICANCE OF THE STUDY: The study focused on comparative quantitative proteomics on Apostichopus japonicus respiratory tree using iTRAQ in responses to multiple climate change stressors: heat, hypoxia and the combined stress. Data showed that A. japonicus can have an acute reaction in diverse biological pathways to both individual and interacting environmental stress, including substance metabolism, signal transduction, protein synthesis, immune response and energy production. Results indicated that sea cucumber adopted different strategies to cope with varied environmental stress, and the interaction between these two stressors has an additive effect at the proteome level. These results offer insight into the molecular regulation of A. japonicus to multiple environmental stress and reveal possible molecular events in sea cucumber under climate changes. The understanding of adaptive variation under global climate changes in aquatic organisms could be improved., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The sea cucumber, an important economic species, has encountered high mortality since 2013 in northern China because of seasonal environmental stress such as hypoxia, high temperature, and low salinity. MicroRNAs (miRNAs) are important in regulating gene expression in marine organisms in response to environmental change. In this study, high-throughput sequencing was used to investigate alterations in miRNA expression in the sea cucumber under different levels of dissolved oxygen (DO). Nine small RNA libraries were constructed from the sea cucumber respiratory trees. A total of 26 differentially expressed miRNAs, including 12 upregulated and 14 downregulated miRNAs, were observed in severe hypoxia (DO 2 mg/L) compared with mild hypoxia (DO 4 mg/L) and normoxic conditions (DO 8 mg/L). Twelve differentially expressed miRNAs were clustered in severe hypoxia. In addition, real-time PCR revealed that 14 randomly selected differentially expressed miRNAs showed significantly increased expressions in severe hypoxia and the expressions of nine miRNAs, including key miRNAs such as Aja-miR-1, Aja-miR-2008, and Aja-miR-184, were consistent with the sequencing results. Moreover, gene ontology and pathway analyses of putative target genes suggest that these miRNAs are important in redox, transport, transcription, and hydrolysis under hypoxia stress. Notably, novel-miR-1, novel-miR-2, and novel-miR-3 were specifically clustered and upregulated in severe hypoxia, which may provide new insights into novel "hypoxamiR" identification. These results will provide a basis for future studies of miRNA regulation and molecular adaptive mechanisms in sea cucumbers under hypoxia stress., (Copyright © 2017 Huo et al.)

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]

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]

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]

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]

Understanding the physiological changes of oocyte in vitro maturation are important for improving in in vitro fertilization rates and embryonic development. In this study, Apostichopus japonicus gonads were dissected, and the oocytes and gonadal fluid extracted from the gonads were dried in darkness to induce oocyte maturation. The changes in the germinal vesicle breakdown percentage (GVBDP), superoxide dismutase (SOD) activity, and the concentrations of glutathione (GSH), cyclic adenosine monophosphate (cAMP), adenylyl cyclase (AC), protein kinase C (PKC), oestradiol (E2), and metabolites in gonadal fluid–oocyte complexes (GFOC) were detected during desiccation. The GVBDP peaked at 85% after 2 hr of desiccation. The SOD activity and GSH concentration in GFOC increased significantly during desiccation, reaching their maximum values at 0.5 and 2 hr of desiccation respectively (p < 0.05). The concentrations of cAMP, AC, PKC, and E2 decreased significantly during the desiccation treatment (p < 0.05) and reached relatively stable levels after 1 hr of desiccation. After 2 hr of desiccation, among the 68 metabolites detected in the GFOC, the concentrations of 52 metabolites increased and those of 16 metabolites decreased. This study not only provides an effective and simple technique for in vitro induction of A. japonicus oocyte maturation under desiccation stress, but also improves our understanding of gamete biology in this species. [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: 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]

Reproductive success is unpredictable for many cultured echinoderms. And cost of reproduction plays an important role in animal life-history. Therefore, understanding cost of reproduction contributes to improving breeding techniques during broodstock rearing in aquaculture. In this study, energetic costs during breeding were explored in the sea cucumber, Apostichopus japonicus, an important aquaculture species in China, Japan and South Korea. The food intake, digestive functions and energy budget patterns were estimated at different breeding stages. Unexpectedly, in the growing gonad phase of the sea cucumber lifecycle, animals showed a decline in feed consumption (from 4.49 to 2.6 g ind-1 day-1), ingestion rate (from 0.4 to 0.13 g g-1 day-1) and apparent digestive rate (from 14.73% to 10.92%), resulting in a reduced energy input. In addition, the increased energy investment in reproduction (from 1.76% to 15.61%) resulted in a decrease in energy allocated to soma growth (from 17.1% to 5.64%) and self-maintenance (from 47.82% to 34.67%). These results suggest that reproduction impairs energy acquisition ability in breeding A. japonicus. And broodstock can adapt energy shortage by internal adjustment of energy allocation strategy. [ABSTRACT FROM AUTHOR]

The ‘cost of reproduction’ refers to a series of negative effects that reproduction has on females. One behavioural cost of reproduction in vertebrates is the loss of or decrease in motility. Diminished locomotion in gravid individuals has serious potential effects on various behaviours, including locomotion, predation, antipredator, migration and the patrolling of territories. However, there have not been comparable studies on marine invertebrates. To address the cost of reproduction in marine invertebrates, we studied the sea cucumber, Apostichopus japonicus , as a model system. Using time-lapse technology and behavioural analysis software, we analysed the locomotor behaviour of A. japonicus from the nonbreeding to the mature stage. In addition, metabolism in muscle tissue of animals between the nonbreeding and growth stage was tested with ultraperformance liquid chromatography and quadrupole time-of-flight mass spectrometry (UPLC–Q–TOF–MS). The results showed that reproduction had no negative effects on locomotion frequency or maximum velocity. However, the total distance moved and cumulative duration of moving gradually decreased. Therefore, the results suggest that loss of locomotor endurance is the behavioural cost of reproduction in female A. japonicus . Additionally, we found 10 significant metabolic changes in the muscle tissue of animals in the growth stage. These results suggest that oxidative stress and lipid metabolism are potential physiological mechanisms linking reproduction and depressed locomotory performance. [ABSTRACT FROM AUTHOR]

Reproduction of the sea cucumber Apostichopus japonicus is critical for aquaculture production. Gonadal development is the basis of reproduction, and lipids, which are among the main nutrients required for gonadal development, directly affect reproduction. We investigated whether gonadal and intestinal lipid metabolism differed between male and female A. japonicus. Transcriptome analysis of the intestines of sexually mature male and female wild-caught individuals revealed differences in gene expression, with 27 and 39 genes being up-regulated in females and males, respectively. In particular, the expression of the fatty acid synthase gene was higher in males than in females. Metabolome analysis of the gonads identified 141 metabolites that were up-regulated and 175 metabolites that were down-regulated in the testes compared with the ovaries in the positive/negative mode of an LC-MS/MS analysis. A variety of polyunsaturated fatty acids were found at higher concentrations in the testes than in the ovaries. 16 s rDNA sequencing analysis showed that the composition and structure of the intestinal microbiota were similar between males and females. These results suggest that sex differences in intestinal metabolism of A. japonicus are not due to differences in the microbiota, and we speculate that gonadal metabolism may be related to intestinal morphology. This information might be useful in improving the reproductive efficiency of sea cucumbers in captivity. • Male and female Apostichopus japonicus may have different lipid metabolic characteristics. • The expression of FASN in male sea cucumber intestines was up-regulated. • The content of PUFAs (DHA, EPA, and ARA) was higher in sea cucumber testes than in ovaries. • Sex differences in intestinal metabolism of Apostichopus japonicus were not affected by microbiota. [ABSTRACT FROM AUTHOR]

We evaluated the effect of high temperature on Apostichopus japonicus gametes. Gametes were exposed to the optimal temperature (18°C; control) or one of six high temperature treatments (26, 27, 28, 29, 30 and 31°C) and the cleavage rate ( CR) of fertilized eggs was measured as an indication of fertilization ability. At control temperatures (18°C), the male and female gametes had high fertilization ability ( CR ≥95.0%) in 5 h and the time at which 50% of gametes lost the ability to successfully fertilize ( LT50) was 7.03 h. All gametes were non-viable after 9 h. When male and female gametes were both exposed to high temperature, the LT50 was lower than that when female or male gametes were treated individually at the same high temperature ( P < 0.05). The LT50 was lower for male gametes treated alone than for female gametes treated alone. In conclusion, exposure to high temperature results in a decline in fertilization ability of A. japonicus gametes, and this decline was more rapid at higher temperature. The female gametes were more resistant to high temperatures than male gametes. [ABSTRACT FROM AUTHOR]

The sea cucumber, Apostichopus japonicus , is an important marine aquaculture species in Asian countries. The small body size but high fecundity of A. japonicus suggests that using income resources to support gonad development might be an appropriate life history strategy, but the physiological mechanisms involved in this approach remain unclear. In this study, we conducted three experiments to assess the physiological traits that underlie income breeding strategy of the A. japonicus. As inferred by the carbon and nitrogen stable isotope signatures, the results showed that income breeding allows all adults, even individuals with poor body condition and small maternal size, to reproduce annually by flexibly adjusting their reproductive output. In addition, functionally, we found that the sea cucumbers allocate income resources to the demands of reproduction, growth and storage simultaneously during reproduction. However, dynamic changes of activities of Na+/K+-ATPase, hexokinase and pyruvate kinase suggested that income breeding places a metabolic burden on the breeding adults. Our results provided new insights into the physiological mechanisms underlying income breeding strategy in sea cucumbers. • Apostichopus japonicus is an income breeder. • Income breeding allows all adults to reproduce annually by adjusting their reproductive output. • Income resources are simultaneously allocated to the demands of reproduction, growth and storage during reproduction. • Income breeding places metabolic burden on the breeding sea cucumbers. [ABSTRACT FROM AUTHOR]

Sea cucumber Apostichopus japonicus is important aquatic economic species in Asia. In recent years, due to the decline of wild resources of A. japonicus , in order to ensure the sustainable supply of seedlings, the broodstock rearing is particularly important during seedling production, reproduction is also an essential stage in the life history of A. japonicus. However，the physiology of marine animals undergoes variations during the process of reproduction. It is well known that the energy demand of broodstock increases and their immunity decreases during the reproduction. Intestinal microorganisms participate in host life activities, while the presence of pathogens and probiotics will affect host health. However, the function of intestinal microbiota in the energy and immunity during the reproduction remains unclear. In this study, we performed a metagenomic analysis of the gut microbiota in A. japonicus to investigate variations in microbial composition and KEGG pathways associated with reproductive periods. Results suggested that Firmicutes/Bacteroidetes (F/B) was gradually increasing during reproduction, which increased host energy harvest, and was difference between male and female A. japonicus. Virulence Factors of Pathogenic Bacteria (VFBD) upregulated from the gonadal growth period. The higher expression of VFBD during the gonadal growth period than at other times may be caused by the fact that Flavobacteriaceae and Rhodobacteraceae are most abundant during this period. Lysozyme activity was upregulated during reproduction and peaked during the gonadal mature period, with a similar trend of variability as in VFBD, which carried out immunological protection against A. japonicus. The relative abundance of Saccharomycetaceae , and Bacillaceae was highest during the spawning period, and it has been identified that microorganisms strengthen immune protection against A. japonicus during this period, when A. japonicus was in a weakened state. Based on KEGG analysis, expression of oxidative phosphorylation and the fever pathway increased after spawning, indicating that reproduction causes oxidative stress in A. japonicus. Additionally, the differences in several KEGG pathways were related to sex. Overall, by analyzing the energy and immune systems, the study confirmed that intestinal microorganisms play vital physiological roles in broodstock of A. japonicus during reproduction. This study provided important information for breeding and the application of A. japonicus in aquaculture. • Sea cucumber Apostichopus japonicus , is one of the most economically important aquaculture species in Asia. This study confirmed that intestinal microorganisms play vital physiological roles in broodstock of A. japonicus during reproduction, microorganisms participate regulation of host energy metabolism, immune adjustment. • There are several pathogenic bacteria increased during reproduction. Post spawning, the number of probiotics increases, which can protect A. japonicus and provide immune compensation. • The composition of intestinal microbiome is also different in male and female individuals. • Several KEGG pathways changed, focused on energy metabolism and oxidative damage. • This study provided an important information for breeding and the application in aquaculture of A. japonicus. [ABSTRACT FROM AUTHOR]

Protein is a necessary nutrient for the sea cucumber, Apostichopus japonicus , an important commercial species in China, South Korea and Japan. In this study, the dietary protein requirements of two newly discovered color morphs—white and purple was investigated and compared with the common, green morph. The green, white and purple morphs were fed a diet with five different protein levels (1, 6, 11, 16 and 21%) for 60 days with a mixture of soybean meal and fish meal (1:1) as the protein source, and their growth, energy budget, physiological and immunological performance were measured. Results showed that dietary protein levels had a significant effect on the growth performance of A. japonicus (P < 0.05). The maximum specific growth rate (SGR) and proportion of energy allocated for growth occurred at dietary protein levels of 6 and 11%, and the food conversion efficiency (FCE) was highest at the 11% protein level, indicating that the optimum dietary protein level for these color morphs is at ~ 11%. Apparent digestibility coefficients for dry matter (ADMD) and crude protein (ACPD) increased, but the ingestion rate decreased with increasing dietary protein levels, due perhaps to the decreased sea-mud content of the diets. The energy allocated to excretion, and the free ammonia and malonaldehyde content in coelomic fluid increased with increasing dietary protein levels, which can be explained by enhanced protein metabolism. Trypsin activity decreased significantly when dietary protein was > 16%, indicating that the protein content was beyond the digestive ability of sea cucumber, and that excess protein in the diet inhibits protein digestion. Catalase (CAT) and glutamic–oxaloacetic transaminase activity was positively and significantly correlated with SGR, indicating that rapid growth was supported by a robust immune system and effective protein metabolism. At a 1% dietary protein level, the purple color morph had significantly higher SGR, FCE, ACPD and CAT activity, and allocated more energy for growth than the green morph, indicating that the purple morph may be better adapted to a low protein diet than the green morph. The white morph had lower SGR, FCE, superoxide dismutase (SOD) and CAT activity, and allocated less energy to growth, but had a higher excretion energy and higher free ammonia content in coelomic fluid than the green or purple morphs, indicating a difference or physiological defect in protein metabolism in the white morph. Statement of relevance The results of this study would be invaluable in improving aquaculture technology and management strategies for green, white, and purple color morphs of Apostichopus japonicus . [ABSTRACT FROM AUTHOR]

The sea cucumber Apostichopus japonicus (Selenka) tolerates salinity fluctuations when inhabiting the intertidal zone and culture ponds. In this study, green, white and purple morphs of juvenile A. japonicus (1.0 ± 0.1 g) were cultured at salinities of 22, 26, 30, 34 and 38 for 60 days. The influence of salinity on the growth, energy allocation and physiological performance of A . japonicus was determined. The results indicated that the three color morphs tested could survive within the salinity range of 22–38. Salinity had a significant effect on the growth, energy allocation and physiological performance of sea cucumbers ( P < 0.05). Specific growth rates, ingestion rates and feed conversion efficiencies of A. japonicus were generally optimal at a salinity of 30. Similar results were obtained for energy ingested, and the proportion of energy allocated to growth. Significant changes in enzyme activities of sea cucumbers mainly occurred at salinities of 22 and 38, indicating that metabolism was affected by low and high salinities. Green A. japonicus grew faster than the white and purple color morphs at a salinity of 22. Growth rates were the highest in purple, then green and the lowest in white color morphs at salinities of 30, 34 and 38. At a salinity of 22, the green allocated more energy to growth and respiration. The purple morph allocated more energy to growth and respiration when water salinity reached 34 and 38. At salinities of 30, 34 and 38, the purple morph had higher trypsin and superoxide dismutase activities, which supported the higher specific growth rate and food conversion rates compared with the green and white color morphs. The results clearly showed that the green color morph performed better at low salinities, while the purple was better adapted to high salinities within the tolerance range. [ABSTRACT FROM AUTHOR]