Shuang Zhang

This study comprehensively evaluated the physiological, metabolic, and microbial responses of Litopenaeus vannamei to graded levels of Clostridium autoethanogenum protein (CAP) used as the primary dietary protein source. The shrimp were randomly assigned to five iso-lipidic experimental diets containing 32%–48% crude protein. The fish meal content was fixed at 15% for each diet, and the protein level of the diet was adjusted by varying the amount of CAP added. The results indicated that: growth performance exhibited a distinct biphasic response, the CAP40 group achieved highest specific growth rate (SGR), whereas higher inclusions (CAP 44%-48%) significantly reduced SGR ( P < 0.05). Broken-line regression analysis identified 39.44% as the optimal dietary protein level for maximizing growth when CAP is the main protein source. Whole-body lipid content of shrimp increased significantly with higher dietary CAP inclusion ( P < 0.05), peaking in the CAP48 group. Physiological analyses showed that CAP40 enhanced intestinal digestion by upregulating the activity and gene expression of amylase, trypsin, and lipase. ( P < 0.05). Microbiota profiling revealed that CAP40 increased gut microbial alpha diversity ( P < 0.05), suggesting greater ecosystem stability. Functional metagenomic prediction using Tax4Fun further elucidated a critical trade-off: Moderate CAP inclusion (CAP40) enriched microbial pathways linked to lipid metabolism and host growth, but concurrently elevated the relative abundance of potential opportunistic pathogens such as Vibrio and Acinetobacter . In contrast, high CAP inclusion (CAP48) shifted the microbial community toward proteolytic amino acid catabolism and reduced pathogen load, yet this was accompanied by dysbiosis dominated by sulfate-reducing bacteria like Fusibacter . Collectively, these findings underscore CAP’s strong potential as a fishmeal replacer but highlight that its benefits are highly dose-dependent. Successful application in shrimp aquafeeds requires precise optimization of inclusion levels to balance growth promotion against the risks of metabolic imbalance and microbial instability.

Clostridium autoethanogenum protein (CAP) offers a sustainable fishmeal alternative, but high inclusion may impair shrimp growth and health. This study evaluated the responses associated with dietary curcumin (CUR) supplementation in Penaeus vannamei fed a diet in which 50% of the fishmeal was replaced with CAP. Three diets were formulated: a fishmeal-based control diet (FM), a low-fishmeal diet in which 50% of the fishmeal was replaced with CAP (CAP), and the CAP diet supplemented with 60 mg/kg CUR (CTER). After an 8-week feeding trial, P. vannamei fed the CAP diet exhibited significantly lower final body weight, weight gain rate, and specific growth rate, accompanied by adverse histological changes in the intestine and hepatopancreas, reduced hepatopancreatic immune enzyme activities, and alterations in the intestinal microbiota. Compared with the CAP group, CUR supplementation was associated with improved growth performance, higher survival following WSSV exposure, improved hepatopancreatic and intestinal morphology, increased immune enzyme activities, greater microbial richness, and shifts in the relative abundance of several dominant bacterial taxa. Transcriptomic analysis further suggested that the beneficial effects of CUR may be partly associated with differential expression of genes enriched in metabolism- and immunity-related pathways. Overall, dietary CUR supplementation was associated with broad improvements in growth, tissue condition, nonspecific immune responses, intestinal microbial profiles, and post-challenge survival under the high-CAP dietary condition. These findings support the potential application of CUR as a functional additive in CAP-based, low-fishmeal diets for P. vannamei.

This study investigated how defatted silkworm pupae meal (DSPM) modulates flesh quality in pearl gentian grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂). A total of 360 size-uniform fish were randomly assigned to four dietary treatments for 8 weeks: D0, the fishmeal (FM) based control diet; and D1, D2, and D3, in which DSPM substituted 25%, 50%, and 100% of dietary FM, respectively, with three replicates per treatment and 30 fish per replicate. Compared with D0, D1 and D2 improved final body weight, weight gain rate, specific growth rate, and feed conversion ratio, whereas D3 reduced survival and feed utilization. For flesh quality, D2 showed the most favorable phenotype, characterized by higher crude protein, collagen, flavor-associated amino acids, pH, texture attributes, and muscle fiber density, together with lower ether extract, cooking loss, freezing loss, and shear force. DSPM substitution also increased unsaturated and polyunsaturated fatty acid proportions and improved lipid health indices. Moderate substitution, especially D2, enhanced oxidative stability by increasing SOD and CAT activities and reducing MDA accumulation. Non-targeted metabolomics combined with qPCR analysis of selected flesh quality-related genes suggested that these improvements were associated with osmotic regulation, collagen remodeling, purine metabolism, membrane lipid homeostasis, nutrient sensing, myogenesis, and antioxidant defense. Complete FM substitution impaired muscle structure, water retention, and redox balance. Thus, 50% FM substitution with DSPM effectively optimized grouper flesh quality in this study.

This study evaluated the effects of dietary CpG oligodeoxynucleotide (CpG ODNs) on growth performance, immunity, digestive function, intestinal microbiota, and transcriptomic responses in Litopenaeus vannamei. Shrimp with an initial body weight of 0.30 ± 0.02 g were fed diets supplemented with 0, 0.1, 0.4, 1.6, 6.4, or 25.6 mg kg⁻¹ CpG ODNs for 8 weeks. Dietary CpG ODNs did not significantly improve most growth parameters; however, shrimp fed the diet supplemented with 1.6 mg kg⁻¹ CpG ODNs showed a lower feed conversion ratio. After white spot syndrome virus challenge, shrimp fed the diet supplemented with 25.6 mg kg⁻¹ CpG ODNs showed higher survival than those in the control group, whereas survival after Vibrio parahaemolyticus challenge did not differ significantly among treatments. Dietary supplementation with CpG ODNs at levels above 0.4 mg kg⁻¹ increased the activities of several serum immune-related and antioxidant enzymes, reduced malondialdehyde content, and enhanced intestinal trypsin and amylase activities. In addition, this treatment increased microbial richness indices, while reducing the relative abundances of Vibrio and Photobacterium. Transcriptomic analysis showed that several pathways, including the AMPK signaling pathway and JAK–STAT signaling pathway, were significantly enriched in the CpG ODNs (above 0.4 mg kg⁻¹) groups compared with the control group. In conclusion, dietary supplementation with CpG ODNs did not significantly improve the growth performance of L. vannamei. However, dietary supplementation with CpG ODNs at levels above 0.4 mg kg⁻¹ may help enhance immune and digestive functions and modulate the intestinal microbiota composition of L. vannamei.

High-lipid, low-protein diets are economically advantageous in aquaculture costs but often induce hepatic damage, immunosuppression and metabolic disorders in carnivorous fish like hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂). Tea saponin (TS) is a bioactive triterpenoid from camellia seed meal with excellent lipid-lowering and anti-inflammatory effects. The purpose of the current study was to investigate the dose-dependent impacts of TS supplementation at 0% (control, T0), 0.05% (T5), 0.10% (T10), 0.15% (T15), and 0.20% (T20) in diets formulated to contain 42% crude protein and 16% crude lipid on juvenile hybrid grouper (17.51 ± 0.03 g), with three replicate tanks per treatment, over a 4-week feeding trial. The results showed that low TS supplementation (0.05%) improved growth, with the effect limited to final average weight (FAW), whereas higher doses (≥0.15%) reduced weight gain. The T5 group exhibited the highest hepatic total antioxidant capacity and superoxide dismutase activity, consistent with the corresponding gene expression, and the lowest malondialdehyde and reactive oxygen species levels. Lysozyme activity and immunoglobulin M content were significantly higher in T5–T15 groups (p < 0.05). Furthermore, appropriate TS significantly upregulated anti-inflammatory cytokines (p < 0.05) and downregulated pro-inflammatory factors. Histologically, 0.10% TS reduced inflammatory infiltration, while high doses caused hepatocyte rupture and lipid vacuolation. Transcriptomic analysis further elucidated that the beneficial effects of low-dose TS were linked to the activation of PPAR signaling, fatty acid catabolism, and cellular quality control pathways, while high-dose TS triggered stress-related and biosynthetic programs. In conclusion, moderate TS supplementation (0.05–0.10%) ameliorated diet-induced oxidative stress and immunosuppression, improved growth performance and anti-inflammatory factor expression, whereas over-addition inhibited growth and exacerbated hepatic damage. Based on a quadratic model, the optimal dietary TS level for maximizing growth under this low-protein, high-lipid regimen is estimated at 0.055%.