In aquaculture, the use of probiotics to improve growth, immunity, and stress resistance in crustaceans has gained increasing attention. This study examined the effects of incorporating different levels of Rhodotorula mucilaginosa (0.0, 0.1, 1.0, and 10.0 g/kg) into the diet on growth performance, antioxidant capacity (AOC), immune function, Toll/Imd, and JAK‐STAT signaling pathways in red claw crayfish ( Cherax quadricanatus ). The investigation was conducted through a 56‐day feeding trial. The main results are as follows: Compared with the control group (0.0 g/kg), different R. mucilaginosa levels significantly increased ( p < 0.05) the specific growth rate (SGR) and weight gain rate (WGR) of red claw crayfish, significantly increased ( p < 0.05) the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione S‐transferase (GST), total AOC (T‐AOC), and acid phosphatase (ACP) in hepatopancreas of red claw crayfish, and significantly upregulated ( p < 0.05) the relative expression levels of tumor necrosis factor receptor‐associated protein 6, akirin, immunodeficiency homolog, interferon regulatory factor 4, Toll‐like receptor (TLR) 6, TLR 2, Janus kinase, signal transducer activator of transcription, tumor necrosis factor α, interleukin‐1β, transforming growth factor‐β1 genes in the hepatopancreas of red claw crayfish. In conclusion, R. mucilaginosa significantly enhanced red claw crayfish’s growth, AOC, and immune function, and activated the Toll/Imd and JAK‐STAT signaling pathways. In this experimental context, the ideal addition level of R. mucilaginosa is 1.0 g/kg.

Mannan oligosaccharide (MOS), a prebiotic derived from yeast cell walls, has been shown to enhance growth performance and health status in various aquatic species. As an exogenous antigen adjuvant, MOS modulates T-cell-mediated immune responses, thereby improving immune function and suppressing excessive inflammatory reactions. This study aimed to evaluate the effects of dietary MOS supplementation on growth performance, serum biochemical parameters, muscle composition, digestive enzyme activity, antioxidant and immune status, and the mTOR signaling pathway in juvenile GIFT tilapia (Oreochromis niloticus). Juveniles (initial body weight: 16.17 ± 1.32 g) were randomly assigned to six treatment groups (three replicate tanks per group) and fed diets supplemented with MOS at 0, 0.2%, 0.4%, 0.6%, 0.8%, and 1% (equivalent to 0, 2, 4, 6, 8, and 10 g/kg of diet, respectively) for 60 days. Compared with the control group, fish fed MOS-supplemented diets exhibited significantly higher (p < 0.05) weight gain rates, specific growth rates, and protein efficiency ratios, along with a significantly lower (p < 0.05) feed conversion ratio. Serum albumin, high-density lipoprotein, and lysozyme levels were significantly increased (p < 0.05), whereas triglycerides, low-density lipoprotein, aspartate aminotransferase, and alanine aminotransferase levels were significantly decreased (p < 0.05). In the liver, head kidney, and spleen, the expression of pro-inflammatory genes (tumor necrosis factor α, interleukin 1β, interleukin 6, interleukin 8, and interferon γ) was significantly downregulated (p < 0.05), while the expression of antioxidant and protective genes (superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, nuclear factor erythroid 2-related factor 2, lysozyme, alkaline phosphatase, interleukin-10, transforming growth factor β, and heat shock protein 70) as well as mTOR signaling pathway-related genes (mammalian target of rapamycin, akt protein kinase B, phosphatidylinositol 3 kinase, and ribosomal protein S6 kinase polypeptide 1) was significantly upregulated (p < 0.05). Overall, MOS positively affects tilapia’s growth, health, and immunity, with 0.60% identified as the optimal dietary level based on growth performance.

This study investigated the effects of dietary supplementation with varying levels (CK: 0.0 g/kg; RL: 0.1 g/kg; RM: 1.0 g/kg; RH: 10.0 g/kg) of Rhodotorula mucilaginosa on muscle composition, serum biochemical indicators, antioxidant capacity, lipid metabolism, and the mTOR signaling pathway in red claw crayfish (Cherax quadricarinatus). Results showed that, compared to CK, treatment groups had higher muscle crude protein, fat, leucine, histidine, arginine, and essential amino acids (p < 0.05), and lower saturated fatty acids (p < 0.05). Treatment groups also exhibited increased activities of alkaline phosphatase, acid phosphatase, superoxide dismutase, catalase, glutathione S-transferase, lysozyme, albumin, total protein, and antioxidant capacity (p < 0.05), with reduced activities of aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, and triglycerides (p < 0.05). In the hepatopancreas, treatment groups showed significant downregulation of AMP-activated protein kinase α, β, and γ, and carnitine palmitoyltransferase 1 genes (p < 0.05). Conversely, genes involved in lipid anabolism (peroxisome proliferator-activated receptor γ, acetyl-CoA carboxylase, fatty acid synthase, sterol regulatory element-binding protein, protein kinase B, and mammalian target of rapamycin 1 and 2) were upregulated (p < 0.05). In conclusion, R. mucilaginosa supplementation affects muscle composition, lipid metabolism, and mTOR signaling. The optimal dose is 1.0 g/kg.

The objective of this study was to evaluate the effects of dietary supplementation with different levels of Rhodotorula mucilaginosa (0.0 g/kg, 0.1 g/kg, 1.0 g/kg, and 10.0 g/kg) on resistance to Aeromonas veronii infection in red claw crayfish (Cherax quadricarinatus) (initial body weight of 0.13 ± 0.06 g). The investigation combined a 56-day feeding trial with a subsequent 7-day infection challenge to assess cumulative mortality, immune and antioxidant enzyme activities, and the relative expression of immune-related genes. During the A. veronii infection test, the cumulative mortalities for the 0.1 g/kg, 1.0 g/kg, and 10.0 g/kg groups were 44.44%, 38.89%, and 38.89%, respectively, all significantly lower (p < 0.05) than that of the control group (58.33%). Compared with the control group, after infection with A. veronii, the activities of acid phosphatase, alkaline phosphatase, catalase, and superoxide dismutase in the hepatopancreas and alkaline phosphatase, lysozyme in the hemolymph of red claw crayfish in the 1.0 g/kg group significantly increased (p < 0.05). The activities of aspartate aminotransferase and alanine aminotransferase in the hemolymph of red claw crayfish in the 1.0 g/kg group significantly decreased (p < 0.05). The relative expression levels of serine protease inhibitor, crustacean hyperglycemic hormone, anti-lipopolysaccharide factor, and superoxide dismutase genes in the hepatopancreas of red claw crayfish in the 1.0 g/kg group were significantly upregulated (p < 0.05). In conclusion, R. mucilaginosa could significantly improve the antibacterial ability of red claw crayfish against A. veronii. In this experimental context, the ideal addition level of R. mucilaginosa is determined to be 1.0 g/kg.

This study investigated the effects of dietary Rhodotorula mucilaginosa supplementation with different concentrations (0.0 g/kg, 0.1 g/kg, 1.0 g/kg, 10.0 g/kg) on red claw crayfish (Cherax quadricarinatus). Four groups were established: control group (CK, 0.0 g/kg), low-dose group (HL, 0.1 g/kg), medium-dose group (HM, 1.0 g/kg), and high-dose group (HH, 10.0 g/kg). The feeding trial lasted for 56 days. The results showed that, compared with the control group, all supplementation groups exhibited significantly reduced feed conversion ratios (p < 0.05). The HM and HH groups demonstrated significant increases in body length growth rate, specific growth rate, weight gain rate, hepatosomatic index, and survival rate (p < 0.05). All supplemented groups showed significantly enhanced trypsin and lipase activities in intestines and trypsin activity in the hepatopancreas (p < 0.05). The HM and HH groups exhibited elevated α-amylase activity in the hepatopancreas (p < 0.05). Compared with the control group, marine red yeast supplementation reduced colonization of potential pathogens while increasing probiotic abundance, effectively improving intestinal microbiota structure. The HM group significantly improved intestinal villus length, width, and muscular thickness (p < 0.05). All supplemented groups showed considerable upregulation of hepatopancreatic genes related to immunity (heat shock protein 70, down syndrome cell adhesion molecule, crustacean antibacterial peptide, serine proteinase inhibitors, crustacean hyperglycemic hormone, anti-lipopolysaccharide factor, lysozyme, and alkaline phosphatase) and antioxidant defense (superoxide dismutase, glutathione peroxidase, glutathione, and catalase) (p < 0.05). These findings indicate that R. mucilaginosa can significantly enhance digestive enzyme activity, maintain intestinal health, improve antioxidant and immune-related gene expression, and promote growth performance in red claw crayfish, with the HM group (1.0 g/kg R. mucilaginosa) showing optimal promotion effects.

The objective of this research was to examine how varying dietary inclusion levels of Lactobacillus plantarum influence the muscle composition, hemolymph biochemical indices, lipid metabolism, and the mTOR signaling pathway in red claw crayfish (Cherax quadricarinatus). Four diets with 0 (CK), 0.10 (LG), 1.00 (MG), and 10.00 (HG) g/kg L. plantarum were formulated, with three replicates of 40 crayfish (average weight: 0.13 ± 0.01 g, average length: 0.58 ± 0.01 cm) in a 56-day trial. Results showed that no significant differences in muscle crude protein, crude lipid, ash, or moisture were observed between experimental and CK groups (p > 0.05), while the contents of multiple essential amino acids (e.g., arginine up to 6.05%, histidine up to 7.52%) and non-essential amino acids (e.g., aspartic acid up to 3.70%, glutamic acid up to 1.76%) were significantly elevated, and the content of muscle C18:0 (a saturated fatty acid) was notably reduced (p < 0.05), while total saturated fatty acids showed no significant variation among all groups (p > 0.05). Hemolymph alkaline phosphatase, transaminases, lactate dehydrogenase, and lysozyme activities, as well as glucose, total protein, and albumin levels, were significantly higher in experimental groups (p < 0.05). Lipid metabolism was upregulated, and the mTOR pathway was inhibited in experimental crayfish (p < 0.05). This study demonstrates that dietary L. plantarum enhances lipid metabolism in red claw crayfish, with 1.0 g/kg L. plantarum identified as the optimal supplementation level.