Search Results (32)

This study was performed to investigate the effects of dietary yeast culture (YC) supplementation on growth performance, digestive function, intestinal inflammatory response, and microbiota composition of largemouth bass Micropterus salmoides (LMB). Six diets were formulated with graded levels of YC (0, 5, 10, 15, 20, and 30 g/kg), referred to as CON, YC5, YC10, YC15, YC20, and YC30, respectively. Each diet was assigned to four replicate tanks of LMB juveniles (initial body weight 8.11 ± 0.05 g) with twenty fish per tank. After an 8-week feeding trial, final body weight and specific growth rate showed an increasing trend with 5~20 g/kg YC and reached a maximum at 15 g/kg YC. Feeding ratio decreased, but feed efficiency ratio (FER) improved in response to dietary YC inclusion, and FER was higher in the YC10 fish than in the YC5, YC20, and YC30 fish. Proximate composition (moisture, protein, and lipid) of the whole fish was not affected by dietary YC levels. The activities of intestinal lipase and trypsin were higher in the YC10 fish, while the relative expression of interleukin-8 (il-8) and il-1β was downregulated in the hindgut of the YC15 fish compared with the CON fish. Histological examination showed that the villus height of the midgut, together with goblet cell density of the foregut and midgut, was higher in the YC10 and YC30 fish than in the CON fish. 16S rRNA sequencing showed that Proteobacteria, Fusobacteria, and Firmicutes dominated the intestinal microbiota in LMB. The decrease in harmful Mycoplasma accounted for the dramatic change in Firmicutes abundance, while the increase in Cetobacterium (specifically C. somerae) accounted for the change in Fusobacteria abundance in the gut of the YC10 and YC30 fish compared with the CON fish. The increase in the beneficial Endozoicomonas was the main reason for the change in Proteobacteria abundance in the intestine of the YC30 fish as compared with the CON fish. Taken together, the alteration of intestinal microbiota composition contributed to the improved digestive function and feed utilization in LMB fed YC-supplemented diets. Based on growth performance, the optimal YC level in the diet for LMB was 15 g/kg. Full article

This study examines the impact of the arginine/lysine ratio in feed on the growth, serum amino acids, arginine metabolism, and antioxidant capacity of juvenile largemouth bass (5.95 ± 0.02 g). Five isonitrogenous and isolipidic diets with varying arginine/lysine ratios were formulated and administered over an eight-week period. The results indicated that the treatments had no significant effect on protein efficiency ratio (PER), daily feed intake (DFI), or morphological indices of juvenile largemouth bass (p > 0.05). When the arginine/lysine ratio was 0.85 (2.25/2.65; 2.54/3.00), liver antioxidant capacity was maximized, and inflammatory factors were suppressed. Conversely, a ratio of 2.25/2.99 significantly reduced weight gain (WG) and specific growth rate (SGR) in juvenile largemouth bass, inhibited arginase activity, and increased serum total nitric oxide synthase (T-NOS) activity. When lysine was in excess (2.25/2.99 group), elevating arginine content (2.54/3.00 group) enhanced growth, antioxidant, and immune performance. Analysis of glutathione metabolism and innate immune-related pathway revealed that an optimal arginine/lysine ratio mitigates inflammatory damage induced by oxidative stress. An arginine/lysine imbalance significantly elevated liver malondialdehyde (MDA) content while reducing total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT) activities, and glutathione (GSH) content, thereby increasing the expression levels of inflammatory factors (IL1B, IL8, TGFB1, BAX). These findings demonstrate that an imbalance in arginine/lysine adversely affects the growth, metabolism, and antioxidant capacity of largemouth bass. When lysine is in excess, increasing the arginine content to achieve an arginine/lysine ratio of 0.85 alleviates the negative effects of antagonism, suggesting arginine supplementation may regulate oxidative damage caused by lysine excess. Full article

Aquaculture plays a crucial role in China’s agricultural sector, with improved growth performance and feed efficiency in cultured species representing key industry challenges. Among nutritional strategies, feed attractants have received increasing attention for their ability to stimulate feeding behavior and enhance feed utilization. This study hypothesized that dietary supplementation with a formulated feed attractant would enhance feeding activity, improve physiological condition, and modulate antioxidant and immune responses in juvenile largemouth bass (Micropterus salmoides). A total of 270 fish (initial weight: 12.5 ± 2.5 g) were randomly assigned to three groups: CON (basal diet), YXX0.05 (basal diet + 0.05% attractant), and YXX0.1 (basal diet + 0.10% attractant). After 56 days of feeding, no significant differences were observed in final body weight (FBW) or whole-body composition (p > 0.05). However, feed intake (FI) increased by 5.1%, and the condition factor (CF) improved significantly by 7.6% (p < 0.05) in the YXX0.05 group, while the viscerosomatic index (VSI) was reduced by 3.6% (p < 0.05), suggesting enhanced feeding motivation and improved body compactness. In terms of physiological responses, compared to the control group, the YXX0.05 group exhibited a significant increase in liver total antioxidant capacity (T-AOC) (p < 0.05), a significant decrease in malondialdehyde (MDA) content (p < 0.05), an increase in serum lysozyme (LZM) activity (p < 0.05), and a significant decrease in aspartate aminotransferase (AST) activity (p < 0.05), reflecting enhanced immune status and potential liver protection. In conclusion, although growth performance metrics such as FBW and specific growth rate (SGR) remained unchanged, the feed attractant at 0.05% inclusion significantly improved feed intake, body condition, and physiological health markers. These results suggest the attractant has practical value in improving fish welfare and nutrient utilization efficiency, providing a functional dietary strategy for sustainable largemouth bass farming. Full article

Hyperthermia and nitrogenous pollutants like ammonia and nitrite are common risk factors that adversely affect fish health and pose significant threats to the aquaculture industry. However, the impacts of high temperatures on the accumulation of nitrogenous pollutants in the water of the aquaculture systems and their toxicity to farmed fish are not well understood. In this study, juvenile largemouth bass (Micropterus salmoides, LMB) were kept at 28 °C and 34 °C in a closed aquatic system to investigate the effects of higher temperatures on ammonia and nitrite accumulation. The fish were fed 2% of their body weight daily for a 14-day experiment. Ammonia levels gradually increased, peaking on day 7 at 34 °C and on day 9 at 28 °C, then decreased to near zero. Nitrite levels remained low initially and increased rapidly along with the reduction in ammonia levels at both temperatures. The 34 °C high temperature accelerated the accumulation of ammonia and its transformation into nitrite compared to 28 °C. Fish were sampled on day 1 (low ammonia and low nitrite, LALN), day 8 (high ammonia and low nitrite, HALN), and day 14 (low ammonia and high nitrite, LAHN) to explore toxic effects. Successive exposure to high levels of ammonia and nitrite caused oxidative stress in the liver and significant pathogenic changes in the liver and spleen, with more pronounced impacts observed at 34 °C. Significant changes in gene expression were detected in the liver and spleen of fish sampled at HALN and LAHN, compared to those at LALN, with upregulated genes primarily associated with extracellular matrix (ECM) and cytoskeleton organization. A second experiment was conducted at the same temperatures but without ammonia/nitrite accumulation. The results of this experiment confirmed the combined effects of hyperthermia and ammonia/nitrite toxicity on the expression of genes involved in ECM–receptor interaction and TGF-beta signaling. These findings are valuable for optimizing cultivation environments and promoting the health of farmed LMB. Full article

The distribution of saline-alkali water is extensive and is increasing globally each year. Fully utilizing saline-alkali water for aquaculture can help alleviate the scarcity of freshwater resources in global fisheries. As a major economic fish species, the largemouth bass (Micropterus salmoides) holds significant potential for aquaculture in saline-alkali water. In the present study, we evaluated its tolerance to different salinities (0 ppt, 6 ppt, 9 ppt, 12 ppt, 15 ppt, and 18 ppt) and investigated tissue pathology, serum biochemical indicators, enzyme activities of osmolality and antioxidant, and the relative expression of Na-K-2Cl 1a cotransporter (NKCC1a) under different saline stress (0 ppt, 6 ppt, 9 ppt, and 12 ppt). The largemouth bass 96 h mortality rate increased with increasing salinity, and the LC₅₀ for 96 h was 14.28 ppt based on the mortality results. High salinity group (12 ppt) caused gill and intestinal damage, including necrosis and cell shedding, while 6 ppt had no adverse effects, and the 9 ppt between the two salinities showed an adaptive change histologically. Serum osmolality, Na⁺, Cl⁻, and cortisol levels of the high salinity group were significantly higher than of the low salinities (p < 0.05). Similarly, Na⁺/K⁺-ATPase (NKA), Ca²⁺-Mg²⁺-ATPase (CMA), and superoxide dismutase (SOD) activities of 12 ppt peaked at 24 h (15.7 U/mgprot, 11.5 U/mgprot, and 243 U/mgprot), which is significantly different compared to the other three groups (p < 0.05). The expression of NKCC1a was significantly upregulated at 9 ppt and 12 ppt, suggesting its role in osmoregulation. Furthermore, the expression of NKCC1a in the gill is 2–4 times higher than that in the intestine. These results suggested that largemouth bass can be cultured at 6 ppt and selectively bred for tolerance at 9 ppt. NKA activity, cortisol levels, and NKCC1a expression can be used as a marker of salinity suitability. These findings provide insight into the adaptive mechanisms underlying the physiological responses to acute salinity stress and will contribute to improving aquaculture in saline waters. Full article

The influence of dietary glutamate (Glu) was evaluated in a 56-day feeding trial on the growth performance and flesh quality of largemouth bass (Micropterus salmoides). A total of 1170 fish (average body weight 24.05 ± 0.22 g) were randomly allocated into six groups, with three replicates per group. They were fed diets containing Glu in levels of 11.40% (G1), 11.88% (G2), 12.53% (G3), 13.27% (G4), 14.33% (G5), and 15.62% (G6). We found that, over a 56-day feeding period, the final body weight (FBW) of largemouth bass was about 4–5 times the IBW. The FBW, percent weight gain (PWG), specific growth rate (SGR), feed efficiency (FE), and protein efficiency ratio (PER) initially increased and then decreased with elevating dietary Glu levels. Likewise, protein content, lipid content, apparent digestibility coefficient of dry matter (ADC_D), and apparent digestibility coefficient of protein (ADC_P) followed a similar pattern. Supplementation with Glu significantly improved the hepatosomatic index (HSI), viscerosomatic index (VSI), and relative gut length (RGL). Moreover, dietary Glu augmentation noticeably enhanced flesh composition such as muscle protein, ash, lipid, amino acid contents, and polyunsaturated fatty acids (PUFAs). Furthermore, dietary Glu supplementation enhanced muscle physicochemical quality (such as drip loss and pH), textural properties (adhesiveness and cohesiveness), and biochemical indices such as total protein (TP) and salt-soluble protein, while decreasing muscle cathepsin B (CtsB) and lactate dehydrogenase (LD) contents, thereby improving flesh quality. In conclusion, these findings suggest that Glu plays a crucial role in enhancing both growth performance and muscle quality in largemouth bass. The optimal dietary requirement for juvenile largemouth bass was estimated to be approximately 125.1 g/kg of diet based on SGR analysis. Full article

A 12-week aquaculture trial was conducted to evaluate the effects of vitamin B₆ on the intestinal health of largemouth bass (Micropterus salmoides). Six feeds with a vitamin B₆ content of 2.03 (control group), 2.91, 3.30, 6.03, 9.53, and 21.79 mg/kg were prepared. The results were as follows. Regarding digestive efficiency, the 9.53 mg/kg group showed significantly higher activities of AMY, LPS, and TRY compared to the control group; the 6.03 mg/kg group exhibited increased AKP and Na⁺/K⁺ ATPase activities. Regarding immunity, the 6.03 mg/kg group had markedly higher relative expressions of zo-1 and occ than the control group; the 9.53 mg/kg group showed significantly higher relative expressions of il-10, tgf-β, igm, and cd83, while il-8 and tnf-α were notably lower, and nf-κb was noticeably decreased in 21.79 mg/kg group. For antioxidant capacity, the 6.03 mg/kg group had markedly higher activities of CAT, SOD, GSH-Px, and T-AOC levels, compared to the control group; the MDA level in the control group was markedly higher than in the other groups. The relative expressions of nrf2, cat, Cu-Zn sod, and gpx were highest in 9.53 mg/kg group and significantly higher than in the control group. In conclusion, an appropriate level of vitamin B₆ in the feed is vital for protecting the intestinal health of largemouth bass. Full article

The experiment was aimed at examining the influence of adding emodin to feeds on the growth performance, liver immunity, and resistance against Aeromonas veronii infection among juvenile largemouth basses and other potential mechanisms. A total of 540 fish (45 ± 0.3 g) were randomly divided into 6 diets, including EM-0, EM-250, EM-500, EM-1000, EM-2000, and EM-4000 diets, in which 0, 250, 500, 1000, 2000, and 4000 mg kg⁻¹ emodin was added. Following a 60-day feeding test, it demonstrated that the feed conversion ratio (FCR) of juveniles within the EM-500 and EM-1000 groups remarkably exceeded that of the EM-0 group. Subsequently, unlike those in EM-0 group, the fish in the EM-1000 group showed heightened hepatocyte count, induced hepatic lipolysis-associated expression of peroxisome proliferators-activated receptor α (PPARα) and acyl-coenzyme an oxidase (ACO), and reduced the hepatic triglyceride (TG) levels. Additionally, EM-1000 could up-regulate the expressions of nuclear factor erythroid 2-associated factor 2 (Nrf2) and heme oxygenase-1 (HO-1) in livers compared with controls and boost antioxidant enzymes activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT), along with a lower content of reactive oxygen species (ROS) and malondialdehyde (MDA). Meanwhile, the EM-1000 group increased anti-inflammatory cytokines of interleukin-10 (IL-10) while suppressing the interleukin-8 (IL-8) expression of pro-inflammatory cytokines in livers by contrast to controls. In the end, juvenile largemouth bass in the EM-1000 group showed a comparatively highest survival rate, whereas fish in the EM-2000 and EM-4000 groups exhibited a little higher mortality than that of the EM-0 group. To sum up, our study exposed that supplementing emodin with 1000 mg kg⁻¹ in diet could enhance the hepatic antioxidant status and unspecific immunity to reinforce the protective effect on disease resistance, resulting in improving the growth performance in juvenile largemouth bass. Full article

The aim of this study was to investigate the effects of dietary yeast polysaccharide (YPS) supplementation on the growth performance, whole-body composition, antioxidant capacity, and immunity of juvenile largemouth bass (Micropterus salmoides). In this study, five diets with YPS levels of 0.00% (control), 0.05% (0.05Y), 0.10% (0.10Y), 0.15% (0.15Y), and 0.20% (0.20Y) were designed and prepared. A total of 300 healthy fish (3.20 ± 0.03 g) were randomly divided into 15 floating cages (1 × 1 × 1 m) in five different groups, with three replicates per group, for an 8-week culture experiment. The 0.10Y and 0.20Y groups had significantly higher feed conversion ratios compared with the control group. There was no significant effect on any of the other growth indicators. Plasma biochemical indices showed that the 0.10Y group exhibited the highest plasma alkaline phosphatase content and the 0.20Y group exhibited the highest plasma glucose content. Plasma antioxidant indices (total antioxidant capacity, superoxide dismutase, and glutathione) and antioxidant genes (catalase and superoxide dismutase) were elevated in the 0.05Y or 0.10Y groups, and the malondialdehyde content decreased with increasing YPS concentration. Moreover, the 0.05Y group showed significantly higher immune-related gene (nuclear factor-kappa B, interleukin-8, and interleukin-10) mRNA expression. Altogether, our results indicate that dietary YPS supplementation enhances the antioxidant and immune capacity of M. salmoides, but with no positive effect on their growth. Full article

Largemouth bass (LMB, Micropterus salmoides), a commercially important farmed fish, is vulnerable to heat stress. Breeding heat-resistant LMB is highly desirable in the face of global warming. However, we still lack an efficient method to assess the heat resistance of LMB. In this study, the critical thermal maximum (CTmax) and static exposure methods were first performed to assess the heat resistance of LMB juveniles. The CTmax values of the experimental fish (average body weight 9.87 ± 3.14 g) ranged from 39 to 40 °C but were too close together to differentiate the individual heat resistance. Static exposure experiments with varying temperatures and fish groups also did not provide a clear method for determining the heat resistance. To address these limitations, we developed a tiered exposure method, where the temperature was increased step-wise, starting from 28 to 34 °C at 2 °C increments and then at 0.5 °C increments above 34 °C, with each step lasting one day. The heat resistance of the fish was quantified as the lethal cumulative temperature (LCT), allowing for the classification of fish as sensitive or resistant to heat stress based on their LCT values. To correlate the changes in tissue structure and gene expression with the heat resistance, a new batch of LMB juveniles (average body weight 23.66 ± 6.98 g) were subjected to tiered heat exposure. Brain and liver tissues were collected from the control (without heat exposure), resistant and sensitive (still alive but demonstrated abnormal symptoms) individuals when the temperature was maintained at 35.5 °C for 24 h. The liver tissues of the heat-sensitive individuals showed significant damage and increased cell apoptosis (p < 0.05) relative to those of the resistant ones. The ddit3/chop, bax and casp3 genes demonstrated differential expressions in the liver of the sensitive and resistant fish. Additionally, the LMB juveniles (average body weight 84.06 ± 20.95 g) were found to be more heat resistant than the adults from different sources (average body weight 364.29 ± 84.43 g and 545.71 ± 184.56 g). Through the tiered exposure method, extremely heat-resistant individuals were successfully selected from the population (average body weight 22.69 ± 6.89 g). These findings provide valuable insights into the thermal biology of LMB and the potential for breeding heat-resistant LMB varieties. Full article

The aim of this study was to explain the mechanism underlying the liver injury of juvenile largemouth bass Micropterus salmoides in response to high-starch diet intake. Three diets were formulated with different starch levels, being abbreviated as treatment LS (low starch, 8.13% starch), MS (medium starch, 14.1% starch), and HS (high starch, 20.1% starch), respectively. Fish were fed with their respective diets to apparent satiation for 56 days. The results showed that growth retardation of the HS fish was associated with the reduction in feed intake rather than feed utilization. Histological evaluation of the livers showed that vacuolization was the most prevalent characteristic in the MS fish, while ballooning degeneration, apoptosis, fibrosis, and inflammation were observed in the HS fish. Transcriptome profiling suggested that liver inflammation was mediated by Tlr signal transduction, which activated the Pi3k/Akt/Nfκb signaling axis to promote the release of proinflammatory factors including Il-8 and Ip-10. Hepatocyte apoptosis was mediated by the extrinsic pathway through death receptors including Fas and Tnfr, which coordinately activated the Fadd/caspase-8 death signaling axis. An autonomous inhibition program was identified to counteract the apoptosis signal, and the PI3K/Akt signaling pathway might play an important role in this process through regulating the expression of iap and diablo. Liver fibrosis was mediated through the Tgf-β and Hh signaling pathways. Upon secretion, Tgf-β1/3 bound to TgfβrI/II complex on the liver cell membrane, which induced the phosphorylation of downstream Smad2/3. When Hh interacted with the membrane receptor Ptc, Smo was activated to initiate signaling, driving the activation of Gli. The activation of both Smad2/3 and Gli promoted their nuclear translocation thereby regulating the transcription of target genes, which resulted in the activation and proliferation of HSCs. The activated HSCs constantly expressed colla1 and ctgf, which facilitated substantial accumulation of ECM. It should be noted that the molecular mechanism of liver injury in this study was speculated from the transcriptome data thus further experimental verification is warranted for this speculation. Full article

Background: Ammonia, a ubiquitous contaminant in aquatic ecosystems, poses multifaceted threats to fish species at elevated concentrations. Methods: In order to investigate the toxic effects of chronic ammonia stress on the liver of juvenile Micropterus salmoides, the present experiment was conducted to investigate the differences in changes in liver tissue structure, enzyme activities, and metabolomes after 28 days of ammonia exposure (0, 4, 8, and 16 mg/L). Results: The findings revealed that ammonia exposure induced significant oxidative stress in the liver, manifesting in decreased activities of antioxidant enzymes SOD and GSH-Px, elevated levels of GSH, GST, and MDA, and heightened activities of immune enzymes LZM, ALP, and ACP. An increase in ammonia concentration exacerbated liver tissue damage. Metabolome analysis further unveiled perturbations in liver metabolites of Micropterus salmoides exposed to ammonia, with Ala-His emerging as a potentially pivotal functional substance under chronic stress. Specifically, the 4 mg/L group responded to ammonia toxicity by augmenting GSH and L-Carnosine levels, the 8 mg/L group detoxified via upregulation of L-Glutamine, and the 16 mg/L group mitigated toxicity through the urea synthesis pathway. Conclusions: This research offers preliminary insights into the toxicological responses of Micropterus salmoides under chronic ammonia stress. It is suggested that the duration of ammonia concentration exceeding 4 mg/L in high-density aquaculture should not exceed 7 days. Full article

The effects of starvation and refeeding on the gut condition of juvenile largemouth bass (Micropterus salmoides) remain unclear. Therefore, our research aimed to explore these effects. Amylase and lipase activities were remarkably decreased in the starvation (ST) group, yet prominently increased in the refeeding (RE) group (p < 0.05). In addition to the malondialdehyde (MDA) level, catalase (CAT) and superoxide dismutase (SOD) activities were significantly upregulated in the ST group (p < 0.05) in marked contrast to those in the controls; however, the RE group showed no substantial variations in CAT and SOD activities or the MDA level (p > 0.05). During starvation, the expression of Nrf2-Keap1 pathway-associated genes was significantly upregulated (p < 0.05). The comparative levels of TNF-α, IL-1β, and IL-15 were highly increased, with the levels of TGF-β1 and IL-10 apparently downregulated in the ST group; in contrast, these levels were restored to their original values in the RE group (p < 0.05). In contrast to the controls, the ST group showed significantly lower height and width of the villi, muscle thickness, and crypt depth and a higher goblet cell number; however, these values were recovered to some extent in the RE group (p < 0.05). The dominant bacterial phyla in the intestines of both groups were Proteobacteria, Firmicutes, Bacteroidetes, Acidobacteria, and Actinobacteria, with marked inter-group differences in the genera Serratia and Lactobacillus. Metabolomics analysis showed that amino acid metabolism is disrupted during starvation and is restored after refeeding. In summary, this study expands our comprehension of the interaction between oxidative stress and antioxidant defenses among juvenile largemouth bass subjected to starvation and refeeding. Full article

A 9-week experiment investigated the effects of dietary cobalt levels on the growth performance, antioxidant capacity, and immunity of largemouth bass. Six feed groups were designed and each group received different cobalt levels, including 0.129 mg/kg (control group), 0.192 mg/kg, 0.201 mg/kg, 0.233 mg/kg, 0.277 mg/kg, and 0.316 mg/kg. The results show that the control group (0.129 mg/kg diet) had the lowest final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR), and the highest feed conversion ratio (FCR), when compared to the cobalt supplementation groups. Dietary cobalt levels of 0.192 mg/kg increased the body protein content and decreased the body moisture content. Regarding antioxidant capacity, the highest catalase (CAT) activity was found in the 0.277 mg/kg dietary cobalt group, while the malondialdehyde (MDA) content was significantly diminished; the total antioxidant capacity (T-AOC) content and glutathione peroxidase (GSH-Px) activity exhibited the highest values in the 0.192 mg/kg and 0.233 mg/kg dietary cobalt groups, respectively. Regarding gene expression, compared with the control group, the mRNA expression of sod was upregulated in the 0.192 mg/kg, 0.233 mg/kg, and 0.277 mg/kg dietary cobalt groups, while the mRNA expression of gpx was diminished when dietary cobalt levels were below 0.233 mg/kg. In addition, the highest il-10 and tgf-β mRNA expression levels were observed in the 0.201 mg/kg and 0.233 mg/kg dietary cobalt groups, respectively. According to the quadratic regression analysis based on the SGR and FCR, the optimal requirement was 0.24 and 0.26 mg/kg of dietary cobalt, respectively. Full article

This study evaluated the optimal dietary copper (Cu) levels and their effects on growth performance, body composition, and antioxidant capacity in juvenile largemouth bass (Micropterus salmoides). A total of 360 fish (initial average weight (1.67 ± 0.01 g) and initial average length (2.5 ± 0.2 cm)) were randomly assigned to 18 tanks, each containing 20 fish and six dietary Cu concentrations: 2.13 (control), 3.00, 3.66, 4.58, 4.64, and 5.72 mg/kg. The results indicated that fish receiving 3.00 mg/kg of Cu exhibited the best final body weight (FBW), weight gain rate (WGR), and specific growth rate (SGR), with a significantly reduced feed conversion ratio (FCR). While body composition (moisture, protein, lipid, and ash) remained consistent across groups, plasma total protein (TP) levels increased with Cu supplementation. Elevated triglycerides (TG) and albumin (ALB) were noted at 4.64 and 5.72 mg/kg, respectively, while glucose (GLU) levels decreased with an increase in dietary Cu. Antioxidant capacity, assessed via hepatic glutathione (GSH) and the activities of catalase (CAT), and showed significant improvements at 3.00 and 3.66 mg/kg Cu, while superoxide dismutase (SOD) showed the highest activity at a dietary Cu level of 5.72 mg/kg. Additionally, the expressions of tgf-β and tnf-α genes were significantly upregulated at a dietary Cu level of 5.72 mg/kg, while il-8 and il-10 genes were upregulated at dietary 3.66 mg/kg. The expression of nrf2 was significantly upregulated in response to a dietary Cu level of 3.66 mg/kg compared to the control group, and the expression of the keap1 gene was significantly upregulated in the fish fed with 5.72 mg/kg of dietary Cu. The results indicated that appropriate dietary supplementation could promote the growth performance and improve the antioxidant status the immunity of largemouth bass, and the optimal Cu requirement for FCR and SGR were approximately 3.10 mg/kg and 3.00 mg/kg, respectively. Full article