Dietary fish oil levels modulated lipid metabolism, immune response, intestinal health and salinity stress resistance of juvenile Penaeus monodon fed a low fish-meal diet

Effects of Dietary Gracilaria lichenoides and Bacillus amyloliquefaciens on Growth Performance, Antioxidant Capacity, and Intestinal Health of Penaeus monodon

This research sought to assess the effects of dietary supplements with Gracilaria lichenoides and Bacillus amyloliquefaciens, either individually or combined, on the growth performance, antioxidant capacity, and intestinal function of Penaeus monodon. A total of 840 shrimps were randomly assigned to 28 tanks with an average initial weight of (1.04 ± 0.03) g (30 shrimp per tank) with 7 different treatment groups and 4 replicates per treatment. The control treatment (C) consisted of a basal diet; in contrast, the experimental groups were complement with varying levels of G. lichenoides (3% or 8%), either alone (S3 and S8) or in combination with B.amyloliquefaciens at different concentrations (3% G. lichenoides and 109 CFU/g-S3B9; 8% G. lichenoides and 1011 CFU/g B. amyloliquefaciens-S8B11; 109 CFU/g B. amyloliquefaciens-S9; 1011 CFU/g B. amyloliquefaciens-B11). The results indicated that the maximum values of final body weight (FBW) (10.49 ± 0.90) g, weight gain rate (WGR) (908.94 ± 33.58) g, and specific growth rate (SGR) (4.20 ± 0.06) g were perceived in the 3% G. lichenoide diet treatment, and compared with the control group, the difference was significant (p < 0.05). The whole-body lipid content of shrimp in the B9 group was significantly higher than that in the B11 group (p < 0.05), but no significant difference was observed when compared with shrimp fed other diets (p > 0.05). The ash content of shrimp in the B9 group was found to be significantly higher than that in the S3B9 group (p < 0.05). Furthermore, the lipase activity in the stomach and intestines of the experimental groups exhibited a statistically significantly increase compared to the control (p < 0.05). In comparison to the control group, the hepatopancreas of the S3 group exhibited a significant increase in the activities of glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), and antioxidant genes [SOD, catalase (CAT), GSH-Px, thioredoxin (Trx), Hippo, and NF-E2-related factor 2 (Nrf2)] expression levels (p < 0.05). Additionally, the activities of total antioxidant capacity (T-AOC), SOD, peroxidase (POD), and antioxidant genes (CAT, GSH-Px, Trx, and Hippo) in the S3B9 treatment of hepatopancreas showed significant improvement (p < 0.05). The inclusion of dietary G. lichenoides and B. amyloliquefaciens resulted in enhanced relative expression of intestinal lipid metabolism genes (fatty acid synthetase (FAS), lipophorin receptor (LR), fatty acid transport protein 1 (FATP1)) and suppressed the expression of the long-chain fatty acid-CoA ligase 4 (LCL4) gene. Analysis of microbiota sequencing indicated improvements in composition and structure, with notable increases in Firmicutes at the phylum level and Vibrio at the genus level in the S3 group, as well as an increase in Tenericutes at the genus level in the S8B11 group. Overall, the inclusion of dietary G. lichenoides and B. amyloliquefaciens positively impacted the growth, antioxidant capacity, and microbial composition of shrimp, with particular enhancement observed in shrimp fed a supplementary 3% G. lichenoides diet.

Tea Tree Oil Improves Energy Metabolism, Non-Specific Immunity, and Microbiota Diversity via the Intestine-Hepatopancreas Axis in Macrobrachium rosenbergii under Low Fish Meal Diet Administration

Tea tree oil (TTO) is an essential plant oil with diverse antibacterial and antioxidant properties; however, whether the role played by TTO in low fish meal (LF) diets induced the observed effects in the farmed crustaceans remains unclear. Therefore, this study used Macrobrachium rosenbergii as the model crustacean, and an 8-week feeding experiment with NF (normal fish meal), LF (soybean meal replacing 40% fish meal), and LFT (LF with 200 mg/kg TTO) diets was conducted to evaluate the positive effects of TTO under the LF diet. Compared to the NF diet, the LF diet reduced hemolymph antioxidant capacity and non-specific immunity, and induced hepatopancreas apoptosis and damage. However, in comparison with LF, LTF significantly ameliorated morphological impairment in the hepatopancreas, improved hepatopancreas energy metabolism by upregulating the Bcl-2/Bax and Akt/mTOR pathways, and enhanced antioxidant and non-specific immune capacity by activating the NF-κB/NO pathway. In addition, LFT repaired intestinal barrier injury and the imbalance of intestinal microbiota induced by the LF diet. Moreover, the Pearson correlation revealed the variations of the above indicators, which were related to the abundance changes of Klebsiella, Clostridium sensu stricto 12, Thermobifida, Bifidobacterium, and Alistipes, indicating that these microbes might serve as prospective targets for the intestine-hepatopancreas axis to affect hepatopancreas apoptosis, metabolism, and non-specific immunity. In summary, 200 mg/kg TTO supplementation mediated gut microbiota and positively improved energy metabolism and non-specific immunity, thereby alleviating hepatopancreas dysplasia and damage induced by the LF diet in M. rosenbergii.

Dietary Use of Methionine Sources and Bacillus amyloliquefaciens CECT 5940 Influences Growth Performance, Hepatopancreatic Histology, Digestion, Immunity, and Digestive Microbiota of Litopenaeus vannamei Fed Reduced Fishmeal Diets

An 8-week feeding trial investigated the effect of Fishmeal (FM) replacement by soybean meal (SBM) and poultry by-product meal (PBM) in diets supplemented with DL-Met, MET-MET (AQUAVI®), Bacillus amyloliquefaciens CECT 5940 (ECOBIOL®) and their combinations on growth performance and health of juvenile Litopenaeus vannamei. A total of six experimental diets were formulated according to L. vannamei nutritional requirements. A total of 480 shrimp (0.30 ± 0.04 g) were randomly distributed into 24 tanks (4 repetitions/each diet, 20 shrimp/tank). Shrimp were fed with control diet (CD; 200 g/Kg fishmeal) and five diets with 50% FM replacement supplemented with different methionine sources, probiotic (B. amyloliquefaciens CECT 5940) and their combinations: D1 (0.13% DL-MET), D2 (0.06% MET-MET), D3 (0.19% MET-MET), D4 (0.13% DL-MET plus 0.10% B. amyloliquefaciens CECT 5940 and D5 (0.06% MET-MET plus 0.10% B. amyloliquefaciens CECT 5940). Shrimp fed D3 and D5 had significantly higher final, weekly weight gain, and final biomass compared to shrimp fed CD (p < 0.05). Shrimp fed D2 to D5 increased the hepatopancreas epithelial cell height (p < 0.05). Digestive enzymatic activities were significantly increased in shrimp hepatopancreas’ fed D3 (p < 0.05). Meanwhile, shrimp fed D1 had significant downregulation of immune-related genes (p < 0.05). Moreover, shrimp fed D3 and D5 increased the abundance of beneficial prokaryotic microorganisms such as Pseudoalteromonas and Demequina related to carbohydrate metabolism and immune stimulation. Also, shrimp fed D3 and D5 increased the abundance of beneficial eukaryotic microorganism as Aurantiochytrium and Aplanochytrium were related to eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) production which plays a role in growth promoting or boosting the immunity of aquatic organisms. Therefore, fishmeal could be partially substituted up to 50% by SBM and PBM in diets supplemented with 0.19% MET-MET (AQUAVI®) or 0.06% MET-MET (AQUAVI®) plus 0.10% B. amyloliquefaciens CECT 5940 (ECOBIOL®) and improve the productive performance, health, and immunity of white shrimp. Further research is necessary to investigate synergistic effects of amino acids and probiotics in farmed shrimp diets, as well as to evaluate how SBM and PBM influence the fatty acid composition of reduced fishmeal diets and shrimp muscle quality. Nevertheless, this information could be interesting to develop low fishmeal feeds for aquaculture without affecting the growth and welfare of aquatic organisms.

Effects of cysteine addition to low-fishmeal diets on the growth, anti-oxidative stress, intestine immunity, and Streptococcus agalactiae resistance in juvenile golden pompano (Trachinotus ovatus)

As the precursor of taurine, cysteine serves physiological functions, such as anti-oxidative stress and immune improvement. Investigation of cysteine and its derivatives has made positive progress in avian and mammalian species, yet the study and application of cysteine in aquatic animals are relatively rare. Therefore, we evaluated the effects of supplementing a low-fishmeal diet with various levels of cysteine on the growth, antioxidant capacity, intestine immunity, and resistance against Streptococcus agalactiae of the juvenile golden pompano (Trachinotus ovatus). According to our study, exogenous supplementation with 0.6-1.2% cysteine greatly increased the final body weight (FBW) and specific growth rate (SGR) of golden pompano compared to the control group. Under the present conditions, the optimum dietary cysteine supplementation level for golden pompano was 0.91% based on the polynomial regression analysis of SGR. Meanwhile, we found that the Nrf2/Keap1/HO-1 signaling pathway was notably upregulated with the increase of exogenous cysteine, which increased antioxidant enzyme activity in serum and gene expression in the intestine and reduced the level of reactive oxygen species (ROS) in the serum of golden pompano. In addition, morphological analysis of the midgut demonstrated that exogenous cysteine improved muscle thickness and villi length, which suggested that the physical barrier of the intestine was greatly strengthened by cysteine. Moreover, cysteine increased the diversity and relative abundance of the intestinal flora of golden pompano. Cysteine suppressed intestinal NF-κB/IKK/IκB signaling and pro-inflammatory cytokine mRNA levels. Conversely, intestinal anti-inflammatory cytokine gene expression and serum immune parameters were upregulated with the supplementary volume of cysteine and improved intestine immunity. Further, exogenous cysteine supplementation greatly reduced the mortality rate of golden pompano challenged with S. agalactiae. In general, our findings provide more valuable information and new insights into the rational use of cysteine in the culture of healthy aquatic animals.