A 70-day feeding experiment was performed to investigate the effects of dietary vitamin E at different addition levels (0, 100, 200, and 400 mg/kg) on the growth, collagen content, antioxidant capacity, and expressions of genes related to the transforming growth factor beta (TGF-β)/Sma- and Mad-related protein (SMAD) signaling pathway in sea cucumbers (Apostichopus japonicus). The results showed that the A. japonicus in the group with 200 mg/kg vitamin E exhibited significantly higher growth rates, hydroxyproline (Hyp) and type III collagen contents, and superoxide dismutase (SOD) activity, as well as the upregulation of genes related to Tenascin, SMAD1, and TGF-β. Additionally, the A. japonicus in the group with 100 mg/kg vitamin E exhibited significantly higher body-wall indexes, denser collagen arrangements, improved texture quality, higher activities of glutathione peroxidase (GSH-Px) and peroxidase (POD), as well as the upregulation of genes related to collagen type I alpha 2 chain (COL1A2), collagen type III alpha 1 chain (COL3A1), and Sp-Smad2/3 (SMAD2/3). In contrast, the A. japonicus in the group with 400 mg/kg vitamin E showed a decrease in the growth rates, reduced Hyp contents, increased type I collagen contents, collagen fiber aggregation and a harder texture, along with the downregulation of genes related to the TGF-β/SMAD signaling pathway. Furthermore, the A. japonicus in the group with 400 mg/kg exhibited oxidative stress, reflected by the lower activities of SOD, GSH-Px, and POD. These results indicated that A. japonicus fed diets with the addition of 100–200 mg/kg vitamin E had improved collagen retention and texture quality by increasing the activities of antioxidant enzymes and the expressions of genes in the TGF-β/SMAD signaling pathway. However, the excessive addition of vitamin E (400 mg/kg) induced oxidative stress, which could increase the collagen degradation and fibrosis and pose a threat to the growth and texture quality of A. japonicus.

Extreme weather events such as heavy rainfall significantly reduce surface salinity in coastal waters, presenting considerable challenges to the aquaculture of Japanese scallops (Mizuhopecten yessoensis) in shallow cage systems. This study investigated the effects of chronic low-salinity stress on the growth performance, antioxidant capacity, and gene expression profile of M. yessoensis using a 60-day salinity gradient experiment. S33 represents the control treatment with normal seawater salinity (33‰), while S30, S28, and S26 represent experimental groups with progressively lower salinities of 30‰, 28‰, and 26‰, respectively. A decline in salinity was accompanied by an increase in oxygen consumption. The S26 group exhibited a higher ammonia excretion rate (2.73 μg/g·h) than other groups, indicating intensified nitrogen metabolism. Growth was inhibited under low-salinity conditions. The S33 group exhibited greater weight gain (16.7%) and shell growth (8.4%) compared to the S26 group (11.6% and 6%), which also showed a substantially higher mortality rate (46%) compared to the control (13%). At 28‰, antioxidant enzyme activities (T-AOC, SOD, CAT, POD) were elevated, indicating a moderate level of stress. However, at the lowest salinity (26‰), these indicators decreased, reflecting the exhaustion of the antioxidant systems and indicating that the mollusks’ adaptive capacity had been exceeded, leading to a state of stress fatigue. NAD-MDH activity was elevated in the S26 group, reflecting enhanced aerobic metabolism under stress. Transcriptome analysis revealed 564 differentially expressed genes (DEGs) between the S33 and S26 groups. Functional enrichment analysis indicated that these DEGs were mainly associated with immune and stress response pathways, including NF-κB, TNF, apoptosis, and Toll/Imd signaling. These genes are involved in key metabolic processes, such as alanine, aspartate, and glutamate metabolism. Genes such as GADD45, ATF4, TRAF3, and XBP1 were upregulated, contributing to stress repair and antioxidant responses. Conversely, the expressions of CASP3, IKBKA, BIRC2/3, and LBP were downregulated, potentially mitigating apoptosis and inflammatory responses. These findings suggest that M. yessoensis adapts to chronic low-salinity stress through the activation of antioxidant systems, modulation of immune responses, and suppression of excessive apoptosis. This study provides new insights into the molecular mechanisms underlying salinity adaptation in bivalves and offers valuable references for scallop aquaculture and selective breeding programs.

This review aims to advance the development of biofloc technology (BFT), providing more sustainable and efficient practices for the farming of the Japanese sea cucumber (Apostichopus japonicus). BFT is a sustainable aquaculture method that promotes nutrient recycling and effective carbon source management, offering significant advantages such as improving water quality, enhancing growth performance, and boosting the physiological activity and disease resistance of cultured animals. In A. japonicus farming, the optimal carbon source is glucose, and the ideal carbon-to-nitrogen (C/N) ratio ranges between 15 and 20. Microbial additives, such as the Bacillus species, have been shown to enhance biofloc formation and growth, as well as the immune responses in A. japonicus. However, the technology also faces limitations, including finding suitable biofloc culture protocols that match the physiological habits of A. japonicus and potential challenges with biofloc stability under varying environmental conditions. Based on existing research, this review discusses these limitations in the farming of A. japonicus. Additionally, it compares biofloc farming models for other economically important aquatic species. By addressing these key aspects, this review offers insights to enhance BFT performance, ultimately contributing to more efficient and sustainable A. japonicus aquaculture practices.

Sea cucumber (Apostichopus japonicus) is an important economically cultured species in the northern coastal regions of China. Its body wall is rich in collagen, which directly determines product quality and market value. However, with the expansion of aquaculture scale, issues such as insufficient collagen deposition have led to inconsistent quality among cultured individuals. Therefore, there is an urgent need to improve growth performance and body wall quality through nutritional regulation. As functional nutrients, amino acids play key roles in collagen synthesis, yet relevant research on A. japonicus remains limited. This study was conducted to investigate the effects of dietary proline on the growth performance, body wall collagen deposition and organoleptic quality of sea cucumber (initial body weight: 30.20 ± 2.02 g). Three kinds of feed with equal levels of nitrogen and other lipids, and supplemented with different concentrations of proline (0%, 1.5%, 3%) in the basal diet, were named P0, P1.5, and P3, and the experiment was conducted for 60 days. The results showed that supplementation with 3% proline significantly increased final body weight and weight gain rate (p < 0.05), reaching 66.39 g and 115.30%, respectively. Collagen content in the body wall increased by approximately 18.5% compared to the control group. Histological analysis of the body wall showed that the collagen fibers in the P1.5 and P3 groups were thicker, with an increased proportion of type I collagen. Texture profile analysis indicated that hardness, cohesiveness, and chewiness were significantly improved in the P3 group (p < 0.05). In summary, supplementation with 1.5% and 3% proline effectively enhanced growth, collagen deposition, and body wall quality. Compared to the P0 group, the relative expression levels of collagen type I alpha 2 chain (COL1A1), Sma- and Mad-related protein 1(SMAD1), and sp-smad2/3 (SMAD2/3) in the body wall tissue were significantly upregulated in both the P1.5 and P3 groups (p < 0.05).

The histological integrity of the intestine depends on the tight and orderly arrangement of epithelial cells within the intestinal villi. Nodal, a transforming growth factor-β (TGF-β) family member, has been reported to promote epithelial cell proliferation. Collagen not only establishes physical connections between adjacent cells but also serves as an anchoring platform for cell adhesion and regeneration processes. Therefore, a 21-day feeding trial was conducted using RNA interference to investigate the role of the Nodal gene in regulating intestinal collagen synthesis and histological structure integrity in juvenile A. japonicus fed diets containing graded levels of vitamin E (VE) (0, 200, and 400 mg/kg). The results showed that the addition of 200 mg/kg VE significantly improved the growth rate, immune enzyme activities and related gene expression, as well as intestinal villus morphology. Additionally, the addition of 200 mg/kg VE upregulated the expression of Nodal, which activated the expression of collagen synthesis-related genes and promoted collagen deposition in the intestines of A. japonicus. After Nodal gene knockdown, A. japonicus presented a decreased growth rate, damage to the intestinal histological structure, and impaired collagen synthesis, with the most notable findings observed in A. japonicus fed diets without VE addition. However, these detrimental effects were eliminated to some extent by the addition of 200 mg/kg VE. These findings indicate that VE improves immune function and intestinal histological structure in A. japonicus through a Nodal-dependent pathway.