Substituting fish meal with castor meal in diets of hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂): Effects on growth performance, immune response, antioxidant and digestive enzyme activities, gut morphology, and inflammatory-related gene expression

Biotransformation of aquaculture wastewater into aquatic feed protein source: Chlorella sorokiniana nutritional value and safety risk assessment

Aquaculture wastewater contains high concentrations of nitrogen and phosphorus compounds, which can be used as nutrients for microalgal growth. In this study, the ability of Chlorella sorokiniana (C. sorokiniana) to purify aquaculture wastewater from an intensive recirculating aquaculture system (RAS) carp sp. farm was evaluated. We then assessed the safety risk of C. sorokiniana cultured from aquaculture wastewater and conducted an 8-week fish feeding trial to evaluate its nutritional value as a feed protein source. The three diets were supplemented with 0 (FM, control), 5% (MM5) or 15% (MM15) C. sorokiniana to replace the fish meal. A total of 180 healthy gibel carp (Carassius gibelio) of similar size were randomly selected into 9 tanks (20 fish/tank, 3 tanks/group). At the end of C. sorokiniana purifying aquaculture wastewater, DIC and DTC gradually decreased by 80.6% and 16.5%, respectively, whereas DOC increased by 52.2%. The change curve of CODMn was similar to that of DOC, and the removal rates of NH4-N, DTN, DIP and DTP were 93.5%, 86.8%, 36.0% and 26.6%, respectively. The heavy metals and antibiotics contents of C. sorokiniana were low or not detected and conformed to the requirements of the aquatic feed ingredient standards. The ARA, EPA and total polyunsaturated fatty acids contents of C. sorokiniana were 13.67, 33.82 and 76.81% of the total fatty acids content, respectively. At the end of the fish feeding trial, we found that the replacement of fishmeal with C. sorokiniana did not affect the growth of the fish or the amino acids contents of the muscle but promoted the body colour values of the fish and the relative content of n-3 polyunsaturated fatty acids in the muscle. In addition, 5% dietary C. sorokiniana can upregulate the relative expression of cat and increase the activity of CAT in the liver; upregulate the relative expression of the proinflammatory factor inf-γ and the anti-inflammatory factors il-4 and tgf-β; and reduce the relative abundance of pathogenic bacteria, such as Citrobacter, Staphylococcus and Pseudomonas, in the gut of gibel carp. However, 15% dietary C. sorokiniana significantly increased the relative expression of inf-γ and hsp70 in the liver and only reduced the relative abundance of Citrobacter. Overall, C. sorokiniana has the ability to remove nutrients from aquaculture wastewater and can be an alternative protein source for fish. On the basis of growth performance, antioxidant capacity, fatty acid contents of muscle, and the gut microbiota, 5% dietary C. sorokiniana is recommended.

Long-Term Phellodendri Cortex Supplementation in the Tiger Grouper (Epinephelus fuscoguttatus): Dual Effects on Intestinal Health Revealed by Transcriptome Analysis

The tiger grouper (Epinephelus fuscoguttatus), an important mariculture fish in Southeast Asia, faces increasing health issues in recent years. Phellodendri Cortex (PC) is a traditional Chinese herbal medicine that exhibits a variety of beneficial effects on tiger groupers. The effects of PC, however, varies with the period of dietary intervention. This study aims to investigate the long-term effects of 1% PC supplementation on tiger groupers, focusing on growth, immunity, disease resistance, and intestinal gene expression. The tiger groupers (with an initial mean weight of 27.5 ± 0.5 g) were fed with a diet of Phellodendri Cortex supplementation and a control diet for 8 weeks. Our results indicate that the long-term PC supplementation did not affect growth or Vibrio disease resistance in tiger groupers. However, the transcriptome analysis revealed potential damage to the structural and functional integrity of the groupers' intestines. On the other hand, anti-inflammatory and cathepsin inhibition effects were also observed, offering potential benefits to fish enteritis prevention and therapy. Therefore, long-term PC supplementation in grouper culture should be applied with caution.

Host gut-derived Bacillus probiotics supplementation improves growth performance, serum and liver immunity, gut health, and resistive capacity against Vibrio harveyi infection in hybrid grouper (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatus)

Several reports have revealed the vital role that probiotics play in fish growth and health. However, few works are available for host gut-derived probiotics on the growth, immunity, and gut microbiota of fish, especially in hybrid grouper (♀Epinephelus fuscoguttatus × ♂Epinephelus lanceolatus) due to their isolation difficulty and functional verification. This study aimed at assessing 3 host gut-derived Bacillus species' effects on the growth, immune and antioxidant-biochemical responses, haematological parameters, intestinal morphology, immune-related gene expression, gut microbiota, and disease resistance against Vibrio harveyi in hybrid grouper. A total of 480 hybrid grouper (initial weight = 9.03 ± 0.02 g) were randomly allotted into 4 groups, namely, the group fed a basal diet without probiotic inclusion (control, B0), the group fed the basal diet with Bacillus velezensis GPSAK4 (BV), the group fed the basal diet with Bacillus subtilis GPSAK9 (BS), and the group fed the basal diet with Bacillus tequilensis GPSAK2 (BT) strains at 1.0 × 10⁹ CFU/g. After a 6-week feeding trial, the results revealed significant improvements (P < 0.05) in the growth performance, whole fish-body proximate composition, blood haematological parameters, serum, liver, and intestinal biochemical indexes, intestinal morphology, and protection against V. harveyi pathogen in the probiotic-treated groups compared with the untreated. Additionally, the expressions of intestinal tight junction genes (occludin and ZO1), pro- and anti-inflammatory genes, including IL1β, IL6, IL8, TNFα, MyD88, IL10, and TGFβ, were upregulated (P < 0.05) after Bacillus species administration. Host gut-derived Bacillus supplementation shaped the gut microbiota by significantly increasing (P < 0.05) the relative abundance of Proteobacteria, Bacteroidetes, Actinobacteria (except the BS group), Acidobacteria (except the BT group), Cyanobacteria (except the BV and BT groups), and Verrucomicrobia phyla, as well as known beneficial genera (Romboutsia, Turicibacter, Epulopiscium, Clostridium_sensu_stricto 1 and 13, Lactobacillus, and Bacillus), but significantly decreased (P < 0.05) the abundance of Firmicutes, Chloroflexi, and Fusobacteria phyla, and purported pathogenic genera (Staphylococcus and Photobacterium) compared with the control group. Collectively, the results suggest that B. velezensis GPSAK4, B. subtilis GPSAK9 (especially this strain), B. tequilensis GPSAK2 dietary supplementation at 1.0 × 10⁹ CFU/g has positive effects on the intestinal health of hybrid grouper via microbial composition modulation, thus enhancing the assimilation and absorption of nutrients to boost fish growth, immunity, and disease resistance.

Transcriptome analysis reveals modulation of differentially expressed genes in LPS-treated mouse macrophages (RAW264.7 cells) by grouper (Epinephelus coioides) Epinecidin-1

The marine antimicrobial peptide Epinecidin (Epi)-1 has been shown to exert direct antimicrobial and immunomodulatory actions in teleost, mammalian and avian organisms. For instance, Epi-1 can suppress bacterial endotoxin lipolysachcharide (LPS)-induced proinflammatory cytokines in RAW264.7 murine macrophages. However, it remains unknown how Epi-1 might broadly affect non-activated and LPS-activated macrophages. To address this question, we performed a comparative transcriptomic analysis of non-treated and LPS-treated RAW264.7 cells in the presence and absence of Epi-1. Gene enrichment analysis was conducted on filtered reads, followed by GO and KEGG analyses. The results showed that Epi-1 treatment modulated pathways and genes associated with nucleoside binding, intramolecular oxidoreductase activity, GTPase activity, peptide antigen binding, GTP binding, ribonucleoside/nucleotide binding, phosphatidylinositol binding and phosphatidylinositol-4-phosphate binding. Based on the GO analysis results, we performed real-time PCR at different treatment times to compare expression levels of selected proinflammatory cytokines, anti-inflammatory cytokines, MHC, proliferation and differentiation genes. Epi-1 decreased expression of the proinflammatory cytokines, TNF-α, IL-6 and IL-1β, and it increased the anti-inflammatory cytokine TGFβ and Sytx1. MHC-associated genes, GM7030, Arfip1, Gpb11 and Gem, were induced by Epi-1, which is expected to enhance the immune response against LPS. Immunoglobulin-associated Nuggc was also upregulated by Epi-1. Finally, we found that Epi-1 downregulated the expression of host defense peptides CRAMP, Leap2 and BD3. Taken together, these findings suggest that Epi-1 treatment induces orchestrated changes in the transcriptome of LPS-stimulated RAW264.7 cells.

Effects of Five Prebiotics on Growth, Antioxidant Capacity, Non-Specific Immunity, Stress Resistance, and Disease Resistance of Juvenile Hybrid Grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

To explore the short-term health benefits of five prebiotics on hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂), six experimental groups fed with different diets (basal diet, diet control (CON); basal diet + 0.2% fructooligosaccharide (FOS), diet FOS; basal diet + 0.5% chitosan, diet chitosan (CTS); basal diet + 0.2% mannan-oligosaccharide (MOS), diet MOS; basal diet + 0.1% β-glucan (GLU), Diet GLU; basal diet + 0.05% xylooligosaccharide (XOS), diet XOS) were set up, and a 4-week feeding trial was conducted. MOS and XOS significantly improved the growth of hybrid grouper compared to the CON group (p < 0.05). Antioxidant enzyme assay showed that the activity of glutathione peroxidase (GPx) was significantly enhanced in the MOS group, and the content of malondialdehyde (MDA) in the XOS group was significantly lower than in the CON group (p < 0.05). The catalase (CAT) activities were significantly enhanced in all prebiotic-supplemented groups compared with the CON group (p < 0.05). Non-specific immunity assay showed that the activities of alkaline phosphatase (AKP) and lysozyme (LZM) were significantly increased in all prebiotic-supplemented groups compared with the CON group (p < 0.05). The total protein content in the XOS group was significantly increased (p < 0.05), and the albumin (ALB) activity in the MOS group was more significantly increased than that in the CON group. Histological examination of the intestine revealed that muscle thickness was significantly increased in all prebiotic-supplemented groups compared to the CON group (p < 0.05). Villi length, villi width, muscle thickness all increased significantly in the MOS group (p < 0.05). In addition, the crowding stress and ammonia nitrogen stress experiments revealed that the survival rates of the MOS and XOS groups after stresses were significantly higher than those of the CON group (p < 0.05). Though MOS and XOS exhibited similar anti-stress effects, the antioxidant and non-specific immunity parameters they regulated were not the same, indicating that the specific mechanisms of MOS and XOS's anti-stress effects were probably different. After being challenged with Vibrio harvey, MOS and GLU groups showed significantly higher post-challenge survival rates than the CON group (p < 0.05). These findings indicated that among the five prebiotics, MOS and XOS showed the best overall short-term beneficial effects and could be considered promising short-term feed additives to improve the stress resistance of juvenile hybrid grouper.