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Ornithine is an arginine family amino acid and is not incorporated into protein. This study evaluated its role in growth, immune response and acute NH3stress tolerance of Penaeus vannamei. Six diets with graded levels (0.6, 0.9, 1.2, 1.5, 1.8, 2.1 g kg−1) of L-ornithine were formulated, and fed the shrimp for 8 weeks. The growth of shrimp was significantly improved with the dietary ornithine levels increased from 0.6 to 1.5 g kg−1. Feed efficiency, protein efficiency ratio and protein productive value showed a similar trend to the growth performance of shrimp. Whole body protein and muscle lipid of shrimp were significantly increased in shrimp fed 1.8 g kg−1ornithine compared to those fed 0.6 g kg−1ornithine. The contents of several amino acids were increased with the dietary ornithine increased to 1.5 g kg−1. Elevated levels of ornithine increased the Nitric Oxide (NO) content and suppressed arginase activity in the hemolymph. The relative mRNA expression of superoxide dismutase, heat shock protein 70, dorsaland caspase 3were increased with the dietary addition of ornithine, while the mRNA level of arginasewas decreased with the increasing dietary ornithine levels. After 9 h acute NH3stress, mortality of shrimp reduced with the increasing dietary ornithine levels. The relative mRNA levels of superoxide dismutase, heat shock protein 70, dorsaland catalasewere increased with the dietary addition of ornithine after the acute NH3stress. The second-order regression analysis of weight gain and survival after acute stress revealed that the suitable ornithine content in the shrimp diet was 1.4–1.5 g kg−1.

Dietary Clostridium autoethanogenumprotein (CAP) has the potential to replace fishmeal (FM), but excessive CAP substitutions will affect gut health. Bile acids (BAs) have multiple benefits, but little information is available on the effects of BAs on Pacific white shrimp (Litopenaeus vannamei) fed a CAP diet (CAP replacing FM). An 8-week feeding trial were used to investigate the impacts of CAP substitution and BAs addition on structural changes of intestine, apoptosis, inflammatory cytokine and NFκB pathway of intestine, and transcriptomic profiles of hepatopancreas in Pacific white shrimp. Compared to PC (control) treatment, the NC (CAP50, CAP replacing 50% FM) treatment significantly decreased the fold height (FH) and villus length (VL) of midgut, and impaired the mitochondrial cristae. Compared to NC group, the FH was increased in BA1 (CAP50 with 0.03% BAs) and BA2 (CAP50 with 0.06% BAs) groups, the muscle layer thickness (MT) was decreased in BA2 and BA3 (CAP50 with 0.09% BAs) groups, the VL was increased in BA1 group, and the mitochondrial cristae was normal and well-defined in BA1 and BA2 groups (all p < 0.05). The NC increased the genes expression of apoptosis and NFκB signalling pathway, while the BA2 decreased the genes expression of apoptosis, inflammatory cytokine and NFκB signalling pathway. In transcriptomics analysis, a total of 171 differential expression genes (DEGs) were identified in NC group and 50 DEGs in BA2 group. There was 13 DEGs was observed both in NC and BA2 groups. The 5 KEGG pathways were statistically enriched in all treatments, including “Carbon metabolism”, “One carbon pool by folate”, “Glycine, serine and threonine metabolism”, “Amino sugar and nucleotide sugar metabolism”, and “PPAR signaling pathway”. In conclusion, CAP50 substitution impaired the intestinal health and 0.06% BAs addition improved it, both treatments altered the transcriptomics profiles of hepatopancreas in Pacific white shrimp.

Dietary low-fishmeal (FM) have negative impacts on growth performance and metabolic responses in aquatic animals, while Schizochytrium limacinumhave multiple benefits due to its rich contents of docosahexaenoic acid (DHA). However, little information is available on the effects of S. limacinumon Pacific white shrimp (Litopenaeus vannamei) in a low-FM diet (LF). An 8-week feeding trial were used to investigate the impacts of S. limacinumon growth performance, as well as morphological changes, biochemical indicators, antioxidant capacity, and transcriptomic profiles of hepatopancreas in shrimp fed a low-FM diet. Compared to LF diet, 0.3% S. limacinum(LFLD) diet significantly decreased the specific growth rate (SGR), and did not affect the feed conversion rate (FCR) and weight gain rate (WGR); whereas 0.6% S. limacinum(LFHD) diet did not affect the SGR, FCR and WGR. Histological structures of hepatopancreas showed that LFLD and LFHD treatments reduced the number and size of secretory cells and increased the number of storage cells, compared to LF group. LFLD and LFHD diets significantly decreased the concentrations of triglyceride and total cholesterol, significantly increased the levels of glutathione peroxidase and total antioxidative capacity, while did not affect the levels of malondialdehyde and superoxide dismutase. A total of 135 differential expression genes (DEGs) were identified in LFLD group and 108 DEGs were identified in LFHD group (both compared to LF group). Administration of S. limacinumaltered the transcriptomic profiles, while LFHD induced a pattern similar to that of LF. LFLD and LFHD treatments mainly affected the 9 KEGG metabolic pathways, including “Arachidonic acid metabolism” and “Glutathione metabolism”. In conclusion, LFLD treatment impaired the growth performance of shrimp, while LFHD treatment did not affect it; and both treatments improved the morphological structure, lipid accumulation and antioxidant capacity of hepatopancreas.

Oxidized fish oil, as a harmful ingredient in feed, has a negative impact on aquatic animals. But the effect of oxidized fish oil on hybrid grouper (♀ Epinephelus fuscoguttatus× ♂ Epinephelus lanceolatus), especially the intestinal flora, is not yet understood. In the current study, a 65-day raising experiment with diets containing 0 g/kg, 30 g/kg, 60 g/kg, and 90 g/kg oxidized fish oil was performed (called as R, L, M and H group respectively) to investigate the effects of oxidized fish oil on growth performance, whole body composition, serum biochemical index, intestinal digestive enzyme activities and microbiome composition in juvenile hybrid grouper. Oxidized fish oil inhibited growth performance of pearl gentian grouper. The Moisture, crude protein, and ash content in whole body increased as increasing dietary oxidized fish oil content. The vitamin E content and antioxidant enzyme activity in serum including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) were significantly increased as the oxidized fish oil in the diet increased, but malondialdehyde (MDA) content in serum was significantly decreased. Meanwhile, the D-Lactate (D-LA) and interleukin-10 (IL-10) content in serum was promoted by oxidized fish oil, but interleukin-6 (IL-6) content was suppressed. Moreover, the intestinal digestive enzyme activities were promoted by oxidized fish oil. The oxidized fish oil reduced alpha diversity of intestinal bacteria. At the same time, oxidized fish oil changed the structure of grouper intestinal flora according to beta diversity and line discriminant analysis (LDA) effect size. In conclusion, oxidized fish oil inhibited growth performance, changed the composition of the body and caused oxidative stress and inflammation in the body, but it promoted the secretion of digestive enzymes in the intestine. More importantly, oxidized fish oil reduced the diversity of intestinal flora and changed the structure of intestinal flora.

•Dietary supplementation of CDCA alleviated the intestinal damage of Penaeus monodonfed a low fish meal diet.•Dietary supplementation of CDCA increased the intestinal microbial diversity of shrimp.•Dietary supplementation of CDCA decreased the abundance of Proteobacteria and Vibrio.