Tryptophan (Trp) has been well documented to positively regulate nutrient metabolism, immune responses, and intestinal microecological homeostasis in mammals. However, relevant studies regarding its functions in largemouth bass remain limited. Herein, we assessed the impacts of dietary Trp on growth, antioxidant status, intestinal barrier, and disease resistance in largemouth bass. Fish were fed a basal control diet (C) or basal diets supplemented with 0.1%, 0.2%, 0.4%, and 0.8% L‑Trp for 60 days. Dietary L‐Trp supplementation significantly improved FBW, WGR, and SGR of largemouth bass, with the maximum values found in the 0.4%Trp group. Based on the WGR and SGR data, quadratic regression analysis further identified 0.49% as the optimal dietary L‐Trp inclusion level. In terms of antioxidant capacity, the 0.4%Trp group exhibited markedly higher serum and intestinal activities of CAT, GSH‐PX, and SOD, as well as a higher content of T‐AOC, compared to the C group. Moreover, the 0.4%Trp group significantly upregulated intestinal Nrf2 expression and downregulated Keap1 expression. Relative to the C group, dietary Trp supplementation significantly elevated intestinal villus height and muscular layer thickness in the 0.1%, 0.2%, and 0.4% Trp groups. Consistently, the mRNA levels of intestinal tight junction genes ( ZO-1 , Claudin-1 , and Claudin-4 ) were upregulated in the 0.4%Trp group. Supplementation with 0.4%Trp significantly downregulated the expression of proinflammatory cytokines ( TNF-α , IL-1β , and IL-8 ) and upregulated the expression of antiinflammatory cytokines ( TGF-β1 , IL-10 , IL-22 , and AHR ). Intestinal microbial analysis further revealed that dietary L‐Trp supplementation enriched the abundance of beneficial bacteria, reduced pathogenic microbial populations, and improved intestinal microbial diversity and richness. Finally, dietary L‐Trp supplementation effectively improved the survival rate of largemouth bass following an Aeromonas hydrophila challenge. This was associated with enhanced serum activities of LZM, AKP, and ACP, as well as increased intestinal T‐SOD activity. Additionally, L‐Trp supplementation upregulated the expression of Nrf2 , TGF-β1 , IL-10 , and IL-22 . In contrast, the 0.4%Trp group reduced the MDA content and downregulated expression of Keap1 , HSP70 , TNF-α , IL-1β , and IL-8 . Collectively, 0.4% dietary Trp strengthens antioxidant defense, remodels intestinal microbiota, improves intestinal physical and immune barriers, and enhances resistance against A. hydrophila infection in largemouth bass.
Barley can potentially replace wheat in aquaculture feed. However, barley contains relatively higher fiber and β‐glucans levels, which may reduce digesta viscosity, and hinder endogenous enzyme activities. Supplementation of exogenous enzymes in barley‐based diets could aid in hydrolyzing the non‐starch polysaccharides (NSP). To investigate the effects of enzyme supplements in barley‐based diets replacing wheat, a 5‐week growth trial was conducted on Pacific white shrimp ( Litopenaeus vannamei ). Six isonitrogenous (~35%) and isolipidic (~8%) diets were formulated, namely, whole wheat‐based (17.42%) basal diet (BW); barley‐based basal diet (BB); and four enzyme‐supplemented diets were BB supplemented with either xylanase (XYL) or a multienzymatic solution (MES) which contains pectinase, protease, phytase, β‐glucanase, XYL, cellulase, and amylase. XYL and MES amount was determined based on manufacturers’ recommended dose (low, L) (0.01 and 0.05 g/100 g diet, respectively) and double the recommended dose (high, H) (0.02 and 0.10 g/100 g diet, respectively) and denoted as BB:XYL‐L, BB:XYL‐H, BB:MES‐L, and BB:MES‐H. Shrimp (0.72 ± 0.03 g) were stocked in 108‐L aquaria. Diets were randomly assigned, with six tanks per treatment. At the completion of the trial, growth performance, apparent digestibility coefficients (ADCs), and physiological gene expression in hepatopancreas were analyzed. Growth parameters showed no significant differences ( p > 0.05). However, significant differences in ADC of energy ( p = 0.010) and dry matter ( p = 0.001) were observed. The BB:XYL‐L diet significantly increased energy digestibility compared to BB group. No significant differences in hepatopancreatic gene ( tor , tghsr1l , cat , tgfβ , propo , lgbp , and hsp70 ) expression were detected among treatments ( p > 0.05), although clustering patterns suggested similarity between multienzyme and wheat‐based diets. Overall, barley can replace wheat in Pacific white shrimp diets without impairing growth, while XYL supplementation may improve energy utilization.
High‐carbohydrate‐high‐fat (HCHF) diets often induce glycolipid metabolism disorders, Hepatosomatic fat deposition, and compromised growth in fish. Myo‐inositol (MI) is a known metabolic regulator, yet its specific mechanism in mitigating HCHF‐induced metabolic stress in Yellow River carp remains unclear. This study investigated the effects of dietary MI on growth, glycolipid metabolism, and bile acid signaling in fish fed HCHF diets. Six experimental diets were formulated: a control diet, an HCHF diet, and the HCHF diet supplemented with graded levels of MI (125, 250, 500, and 1000 mg·kg −1 ). After a 9‐week feeding trial, results showed that MI supplementation dose‐dependently improved growth performance (FBW, WGR, and SGR) and feed utilization (FCR), while significantly reducing the hepatosomatic index (HSI). Physiologically, MI reduced serum glucose and triglycerides (TGs), as well as hepatopancreatic total cholesterol (T‐CHO) and TG levels, while elevating high‐density lipoprotein cholesterol (HDL‐C), suggesting enhanced lipid transport capacity. Regarding glycolipid metabolism, MI promoted glycolysis by increasing hk and pfk mRNA expression, while suppressing gluconeogenesis ( pepck ) and lipogenesis ( fas , pparγ ). These metabolic changes were accompanied by alleviated hepatocyte vacuolation and morphological abnormalities, with reduced hepatocellular vacuolation and lipid deposition in HCHF‐fed fish. Mechanistically, bile acid metabolism and phosphatidylinositol 3‐kinase (PI3K)/Akt (protein kinase B) signaling pathways participated extensively and served important roles in the action of MI. Based on comprehensive analysis of growth and physiological indicators, the optimal MI supplementation level in the HCHF diet is recommended as 230–475 mg·kg −1 . In conclusion, MI alleviates HCHF diet‐induced metabolic disorders and hepatopancreatic morphological abnormalities in Yellow River carp, and this effect is associated with the PI3K/Akt and farnesoid X receptor (FXR)/SHP (small heterodimer partner) pathways, providing a theoretical basis for functional feed development for fish.
The study investigated the optimal dietary protein and lipid levels for greenfin filefish ( Thamnaconus septentrionalis ) using two sequential, growth trial‐based experiments with practical formulations. Experiment I was designed to establish the quantitative protein requirement. Six isolipidic and isoenergetic diets with graded crude protein levels (38%, 41%, 44%, 47%, 50%, and 53% of dry matter) and a fixed lipid content of 10% were fed to triplicate groups of fish (5.56 g) for 56 days. Growth performance, feed utilization, and physiological responses were evaluated. Weight gain, specific growth rate, and feed conversion ratio all showed significant quadratic responses to dietary protein level, peaking at 47% protein. Quadratic regression analysis based on growth pinpointed the optimal dietary protein requirement at 45.93%–45.99%. This optimal level not only yielded the highest final biomass and best feed efficiency but was also associated with the highest hepatic total antioxidant capacity (T‐AOC), indicating an enhanced systemic antioxidant defense without provoking oxidative damage, as malondialdehyde (MDA) levels remained stable across all protein groups. Subsequently, Experiment II was conducted to determine the lipid requirement at the established optimal protein level (46%) by testing six isonitrogenous diets with graded lipid levels (6%, 7.5%, 9%, 10.5%, 12%, and 13.5%). Quadratic regression based on growth revealed an optimal dietary lipid range of 9.69%–10.39%. While lipid levels up to 10.5% promoted growth and improved feed conversion through a protein‐sparing effect, inclusion levels exceeding 12% induced metabolic dysfunction. This was evidenced by a sharp decline in T‐AOC and superoxide dismutase activity, a significant increase in MDA, elevated hepatosomatic index (HSI), and reduced lipid retention efficiency. Notably, the concurrent accumulation of hepatic unsaturated fatty acids and rise in MDA at high lipid intakes suggested these endogenous pools became substrates for peroxidation, overwhelming the antioxidant system. Therefore, a practical formulation containing 46% protein, 9.7%–10.4% lipid, and 33% carbohydrate, with a crude protein‐to‐gross energy ratio (CP/GE) of ~23.93–24.59 mg/kJ, is recommended for juvenile greenfin filefish (<20 g).
The present study evaluated the effects of dietary phytoadditive supplementation on growth, nutrient utilization, physiological responses, and disease resistance against Vibrio parahaemolyticus in Pacific white shrimp ( Penaeus vannamei ). Four diets, isonitrogenous, isolipidic, and isocaloric, included phytoadditives (turmeric, garlic, ginger, and tamarind in 0.25:0.25:0.25:0.25 ratio) at 0% (control), 0.5%, 1%, and 1.5%. Juvenile shrimp with an initial mean weight of 1.57 ± 0.03 g were randomly placed into 16 tanks. Each tank contained 500 L of water and 50 shrimp. Each treatment diet was allocated to four replicate tanks ( n = 4). The shrimp were fed four times daily at 06.00, 10.00, 14.00, and 18.00 H for 60 days. At the end of the feeding trial, dietary supplementation with the combined phytoadditives significantly improved the growth performance and nutrient utilization of P. vannamei . Shrimp fed the 1% combined phytoadditives had higher ( p < 0.05) weight gain (16.14 ± 0.32 g), specific growth rate (4.03 ± 0.06% day −1 ), and protein and lipid efficiency ratios (1.79 ± 0.05 and 12.10 ± 0.37) than those fed the other diets, with a correspondingly lower feed conversion ratio (1.53 ± 0.05). However, the combined phytoadditives did not significantly affect the whole‐body nutrient composition of P. vannamei . Shrimp fed the 1% combined phytoadditive diet showed significantly ( p < 0.05) higher protease (23.02 ± 1.85 U/mg protein % over control) and lipase (18.13 ± 1.52 U/mg protein) activities in the intestine and amylase activity (2.78 ± 0.21 U/mg protein) in the hepatopancreas. Conversely, intestinal amylase, hepatopancreatic protease, and lipase activities were not significantly influenced by the different inclusion levels of the combined phytoadditives. Shrimp fed the 1% combined phytoadditive diet showed significantly higher ( p < 0.05) superoxide dismutase (SOD) (29.43 ± 2.52 U/mg protein) and glutathione peroxidase (GPx) (0.009 ± 0.001 U/mg protein) activities in the intestine and catalase (CAT) activity (1.30 ± 0.22 U/mg protein) in the hepatopancreas. In contrast, CAT activity in the shrimp intestine and SOD and GPx activities in the hepatopancreas were not significantly affected by the dietary treatments ( p > 0.05). Significantly upregulated Toll‐like receptor (TLR), immune deficiency (IMD), and lysozyme (LYZ) relative mRNA expression was observed in shrimp fed a diet supplemented with 1% combined phytoadditives. Dietary supplementation with 1% combined phytoadditives significantly reduced cumulative mortality during the challenge study (28.12 ± 6.25% versus 53.12 ± 6.25% in the control), corresponding to a relative percent survival (RPS) of 47.1%, compared with 17.6% and 38.9% at the 0.5% and 1.5% inclusion levels, respectively. In conclusion, dietary supplementation with 1% combined phytoadditives improved overall growth performance and immune response in Pacific white shrimp.
