The market value of sea urchin gonads is determined by the specific characteristics associated with gonad size and texture. Formulated feeds can effectively promote the gonad growth of sea urchins but cannot assure essential gonad texture traits. The objective of this study was to investigate the impact of vitamin C (VC) on the gonad growth, texture, collagen content, and the expression of genes involved in the collagen synthesis of sea urchins (Mesocentrotus nudus). Graded amounts of VC (0, 3000 and 6000 mg/kg) were supplemented to make three formulated feeds. Fresh kelp (Saccharina japonica) was used as the control diet. Each diet was randomly distributed to three tanks of M. nudus. The results indicated that the gonadosomatic index (GSI) and texture traits of M. nudus fed C3000 were significantly greater than those fed C0 and C6000. Collagen type I (Col I) in the gonads of M. nudus fed C3000 showed significantly greater areas than those fed C0 and C6000. Consistently, the expression levels of collagen alpha-1 (colp1α) of M. nudus fed C3000 were significantly higher than those fed C0 and C6000. As for the transforming growth factor beta (tgf-β)/Smads pathway, the expression levels of collagen synthesis genes (tgf-β receptor 1 and 2, smad nuclear-interacting protein 1 (snip1) and prolyl 4-hydroxylase subunit beta (p4hβ)) in the C3000 group were significantly greater than those in the C0, C6000 and kelp groups. On the contrary, the expression levels of collagen degradation genes (lysyl oxidase-like 2 (loxl2) and matrix metalloproteinase 14 (mmp14)) in the C3000 group were significantly lower than those in the C0, C6000 and kelp groups. In conclusion, VC at an addition level of 3000 mg/kg significantly increased the gonad texture and collagen contents of M. nudus, which could be accomplished by increasing collagen synthesis and inhibiting collagen degradation through the tgf-β/Smads pathway. These results could contribute to better understanding the beneficial effects of VC addition on the gonad texture quality of M. nudus.

The objective of this study was to investigate the effects of Scoparia dulcis extract (SDE) on stress induced by high stocking density and Cu and trichlorfon exposure in crucian carp (Carassius auratus). The results showed that these stressors exerted detrimental effects in fish, such as inhibition of growth performance, reduced feed intake, and interruption of fish locomotion. Under high stocking density, dietary SDE supplementation increased the content of reduced glutathione (GSH) and the activities of amylase, catalase (CAT), and glutathione reductase (GR) and decreased the content of malonaldehyde (MDA) in the intestine of crucian carp. A similar trend was presented in the hepatopancreas under Cu exposure. Dietary SDE supplementation enhanced the activities of CAT, superoxide dismutase (SOD), glutathione peroxidase (GPx), lactate dehydrogenase, glutamate-oxaloacetate transaminase, and glutamate-pyruvate transaminase in the muscle of crucian carp under trichlorfon exposure. The optimum dietary SDE supplementation levels were 4.07, 4.33, and 3.95 g kg⁻¹ diet based on the recovery rate of weight gain (RWG), feed intake (FI), and inhibitory rate of rollover (IR) for crucian carp under high stocking density and Cu and trichlorfon exposure, respectively. Overall, dietary supplementation with SDE may be a useful nutritional strategy for relieving these stresses in aquatic animals.

Rapid and coordinated test growth is crucial for maintaining the normal body shape of Strongylocentrotus intermedius juveniles. In total, 270 S. intermedius (1.19 ± 0.01 g) were randomly assigned to 18 floating cages. Three cages of sea urchins were fed kelp (Saccharina japonica) (control diet) or one of five formulated feeds with different carbohydrate-to-lipid ratios (C/L) (1, 2, 4, 8, and 16) for 90 days. The results suggested that the weight gain rate of S. intermedius fed C/L4 was markedly greater than that fed C/L1 and C/L16 except for kelp, C/L2, and C/L8. The test diameter (TD) and test height (TH) gain rates of S. intermedius fed C/L4 were markedly greater than those fed other dry feeds except for C/L2. The TH/TD of S. intermedius fed kelp was markedly greater than that fed dry feeds, except for C/L1 and C/L2. Juvenile S. intermedius fed C/L2 showed higher test magnesium content, larger holes, and longer and thinner trabeculae than those fed other dry feeds. Overall, juvenile S. intermedius fed C/L4 had the highest body weight gain rate and test growth rate among the formulated feed groups. Juveniles fed C/L2 had the most coordinated test growth reflected by TD/TH, which is comparable to those fed kelp. Therefore, the optimal C/L for rapid and coordinated test growth of juvenile S. intermedius should be higher than 2 but lower than 4.

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).

This research was conducted to evaluate the impacts of pomegranate (Punica granatum L) peel extract (PPE) on the mold growth and moisture content in pellet feeds, as well as the biochemical indicators in tissues and organs of fish. Firstly, six types of pellet feeds were formulated by adding 0% or 0.5% of pomegranate peel powder (PP), petroleum ether extract (PEE), ethyl acetate extract (EAE), ethanol extract (EE), or aqueous extract (AQE) of PP. Moisture content was determined by air-drying 10 g of wet pellet feed from each treatment at 60 °C for 48 h in uniform-sized Petri dishes. Mold growth was evaluated by homogenizing 15 g of 12-week stored pellet feed with 15 mL of purified water, incubating at 25 °C for 4 days, and recording mold growth. The results indicated that PP, PEE, EE, and AQE reduced the mold growth in pellet feeds (p < 0.05). PP, EAE, EE, and AQE increased the moisture content in pellet feeds. Among all additives, EE has the strongest effects on the mold growth and moisture content in feeds (p < 0.05). According to regression analysis of mold and moisture levels, the optimal EE supplementation levels in pellet feeds were evaluated to be 1.284% and 1.485%, respectively. Then, 420 carp (Cyprinus carpio var. Jian, mean initial weight 12.01 ± 0.53 g) were fed diets formulated with EE at graded inclusion levels (0, 0.3, 0.6, 0.9, 1.2, 1.5, and 1.8%) over a 15-day period. The findings indicated that dietary EE improved the digestive and absorptive function in carp (p < 0.05), and this improvement was closely correlated with the upregulated activities of digestive and absorptive enzymes and the strengthened antioxidant capability in carp’s digestive tissues. Regression analysis of feed intake rate indicated that the optimal EE level suitable for carp is 0.906%. Furthermore, dietary EE enhanced the respiratory capacity by improving functional metabolic enzyme activity and antioxidant defense in the respiration-related tissues and organs of fish (p < 0.05). In summary, supplement EE increases the moisture content, inhibits the mold growth in pellet feeds, and improves the respiratory, digestive, and absorptive functions in fish, providing a valuable insight for PEE use as a naturally functional raw material in fish feeds.

This study aims to clarify the dose–response relationship between dietary β-carotene levels and gonadal pigment deposition and regulation mechanisms related to the carotenoid synthesis of Strongylocentrotus intermedius based on a 60-day feeding trial and subsequent transcriptome analysis. Adult sea urchins (initial weight: 9.33 ± 0.21 g) of three cages were given one of the dry feeds with different doses of β-carotene (0 mg/kg, 150 mg/kg, 300 mg/kg) or fresh kelp (Saccharina japonica). The results indicated that the weight gain rate (WGR) of sea urchins increased with the addition of β-carotene, with that of the C300 group being markedly higher than that of the C0 group. The addition of β-carotene significantly improved the redness (a*) and yellowness (b*) values of the gonads, with sea urchins in the C300 group exhibiting closest gonad coloration to those in the kelp-fed group. Meanwhile, β-carotene and echinenone in the gonads of the C300 group showed the highest contents, reaching 1.96 μg/kg and 11.97 μg/kg, respectively. Several differential genes, enriched in the pathways of steroid biosynthesis, oxidative phosphorylation, and ubiquitination, were screened based on transcriptome analysis. Real-time PCR further demonstrated that β-carotene significantly upregulated the expression of cholesterol 25-hydroxylase (CH25H), NADH dehydrogenase subunit 1 (ND1), NADH dehydrogenase subunit 2 (ND2), and NADH dehydrogenase subunit 4 (ND4) while it downregulated the expression of 24-dehydrocholesterol reductase (DHCR24). These results showed that 300 mg/kg β-carotene significantly increased the WGR, redness, and yellowness values, as well as the contents of β-carotene and echinenone in the gonads of S. intermedius. On the one hand, dietary β-carotene increased NADH enzyme activity, which participates in echinenone synthesis by donating electrons for the transformation of β-carotene to echinenone synthesis. On the other hand, the addition of β-carotene inhibited cholesterol synthesis by increasing the expression of CH25H and decreasing the expression of DHCR24, which could in turn increase the fluidity and permeability of the cell membranes and the transport efficiency of β-carotene and echinenone from the digestive tract to the gonads. These results provided fundamental insights into the production of sea urchin gonads with market-favored colors.