Growth Of Bass Research Articles

Effects of partial replacement of fishmeal with Spirulina platensis powder and addition of Spirulina platensis polysaccharide on growth, nutrition, antioxidant capacity and gut microbiota of Micropterus salmoides

Fish is currently considered a primary protein in the human diet, and the high demand for fish will stimulate the growth of aquaculture. However, a lack of high-quality fish feed (fishmeal) has led to a decline in the quality and yield of aquatic products. Therefore, an alternative high-quality protein source for fish meal is required to sustain the industry. This study assessed the effects of incorporating Spirulina platensis (SP) dried powder as a partial replacement for fishmeal and supplementing with S. platensis purified polysaccharides (PSP) on the growth, nutritional value, and health status of the largemouth bass, Micropterus salmoides, to address the challenges of fishmeal scarcity and promote sustainable development in fish aquaculture. Juveniles were fed four isonitrogenous and isolipidic diets containing SP at 0% (SP0), 3% (SP3) and 6% (SP6) and PSP at 0.3% for 56 days. The results showed that both the SP3 and SP6 groups displayed significantly (P < 0.05) improved growth performance and lower hepatosomatic indices than the control diet (SP0). Whole-body crude protein and protein efficiency significantly increased in both the SP3 and SP6 groups compared with SP0 (P < 0.05). Conversely, crude lipid content notably (P < 0.05) decreased in SP3 (5.96%) and SP6 (5.41%) in contrast to SP0 (6.59%). The muscle amino acid composition of the PSP, SP3, and SP6 groups also improved significantly (P < 0.05) compared to that of the SP0. Liver SOD activity was significantly increased from 1.11 U/mg in SP0 to 1.22–1.24 U/mg in SP3 and SP6 (P < 0.05), while MDA levels declined accordingly. Serum triglyceride levels were significantly lower in SP3 than in SP0 (P < 0.05) but remained stable in the SP6 and PSP groups. Low-density lipoprotein cholesterol decreased significantly in the SP3 and SP6 groups, but no significant effect was observed in the PSP group. Alanine aminotransferase activity was significantly (P < 0.05) lower in the PSP, SP3, and SP6 groups than in SP0. Aspartate aminotransferase activity in PSP and SP3 was significantly lower than in SP0 (P < 0.05), but showed no significant difference with SP6 (P > 0.05). Intestinal trypsin and amylase activities significantly improved in the PSP, SP3, and SP6 groups (P < 0.05), and lipase activities in PSP and SP3 increased significantly compared to those in SP0 (P < 0.05). The intestinal microbiome displayed significantly higher Shannon index scores for SP3 (0.83) and SP6 (0.93) than for SP0 (0.61). The relative abundances of the phylum Fusobacteria and genus Cetobacterium were significantly increased, whereas Proteobacteria and Plesiomonas were significantly decreased in the PSP and SP3 groups compared with that in SP0 (P < 0.05). The present study indicated that the replacement of fishmeal with 3–6% SP and 0.3% PSP addition could improve the growth performance, protein efficiency, muscle nutritional value, liver health, antioxidant capacity, intestinal digestive enzyme activity, and intestinal microbiota diversity of the largemouth bass. Therefore, the partial replacement of SP or the addition of PSP has great potential in promoting healthy aquaculture of largemouth bass.

Dietary bile acids inclusion improves dietary carbohydrate utilization, antioxidant capacity and intestinal microbiota and inflammation of largemouth bass (Micropterus salmoides)

The study explored the role of dietary bile acids inclusion in improving dietary carbohydrate utilization, antioxidant capacity and intestinal microbiota and inflammation of largemouth bass (Micropterus salmoides). Two isonitrogenous (50.40%) and isolipidic (12.00%) diets were formulated, containing a positive control with 5% α-starch and a negative control with 10% α-starch, respectively. The other three diets were supplemented with 200 mg, 500 mg, or 1000 mg bile acids kg−1 based on 10% α-starch diet. Different experiment diets were fed to cultured fish twice daily for 8 weeks. The results showed that the growth of cultured fish was inhibited by high carbohydrate diet and hepatic glycogen and lipid inordinate accumulation were induced. Meanwhile, high carbohydrate diet caused liver oxidative damage, but supplementation of bile acids significantly improved the antioxidant capacity. Compared with the negative control group, dietary bile acids supplementation didn't affect the growth of largemouth bass, but significantly reduced hepatic glycogen and lipid inordinate accumulation and the viscerosomatic index and hepatosomatic index. In addition, the increase of dietary carbohydrate increased liver bile acids content, and dietary bile acids inclusion could linearly increase liver bile acids content. Results showed that bile acids supplementation regulated liver bile acid synthesis and metabolism of largemouth bass through activating FXR-FGFR4-CYP7A1 pathway. Meanwhile, bile acids inclusion inhibited the expression of foxo1 and genes related to gluconeogenesis, including g6pc, fbp1 and gs, enhanced the expression of genes related to glycolysis, including pfkl and gk through activating insulin pathway. Moreover, high carbohydrate diet with bile acids supplementation also increased gut microbial diversity, and changed the relative abundance of some phyla and genera related to carbohydrate utilization and energy balance, and improved the intestinal inflammatory response. Those findings indicated that dietary bile acids inclusion improved carbohydrate utilization, antioxidant capacity and intestinal microbiota and inflammation of largemouth bass.

Astragalus polysaccharides, cinnamaldehyde and their complexes affected growth, physicochemical parameters, histomorphology and flesh quality of Largemouth bass (Micropterus salmoides)

Previously, antibiotic was crucial for aquaculture development, but brought many negative effects. Cinnamaldehyde (Cia) and Astragalus polysaccharides (Asp), bioactive ingredients from Astragalus membranaceus and Cinnamomum cassia, have been confirmed their benefits to livestock. This is the first study to investigate the impacts of Cia, Asp and their joint-effect on Largemouth bass (Micropterus salmoides) growth, digestion, histomorphology and flesh quality. Fish with average weight of 72.48 ± 6.81 g were divided into 5 groups, fed with basal feed (M0); supplemented with 1 g Cia/kg diet (C1); 1.2 g Asp/kg (A1); compatibility of 1 g Cia and 1.2 g Asp/kg (CA1); 1 g Cia and 2 g Asp/kg (CA2) for 65-day. The results showed that growth, condition factor (CF) and survival rate (SR) were significantly improved in adding-groups. Especially, the greatest CF, SR, higher feed intake and conversion rate, apparent dry matter digestibility were all measured in CA1 group. The CA1 M. salmoides also exhibited higher triglyceride, aspartate aminotransferase, alanine aminotransferase and low-density lipoprotein cholesterol contents, while total-cholesterol and high-density lipoprotein cholesterol resulting in fat deposition descended in CA1 group. The activity of digestive enzymes markedly strengthened in A1 and CA1 treatments (P < 0.05). It is consistent with stronger digestive ability, the thinner muscle layers, longer villus, thicker columnar epithelium and lamina propria were found in CA1 and A1 groups. In addition, supplemented Asp was helpful to enhance antioxidant capacity of M. salmoides muscle, whilst reducing the malondialdehyde and lipid-peroxide. The nutritional composition was best in the CA1 fillets, richer in protein, least ash and fat. The histological characteristics were improved in CA1 muscles, which is the most resilient. However, most of above indices inhibited in CA2 group, particularly, the intestinal and liver damages occurred. On balance, the supplement with best aquaculture effects is CA1: 1 g Cia+1.2 g Asp/kg diet.

Positive effect of dietary emodin on growth, antioxidant capacity, inflammatory response, intestinal microbiota and resistance of Micropterus salmoides against MSRV infection

This study aims to investigate the effect of emodin on growth and intestinal microbiota of largemouth bass (Micropterus salmoides) larvae. Five diets, including Con, E25, E50, E100 and E200 diet in which 0, 25, 50, 100 and 200 mg·Kg−1 emodin was supplemented. After a 30-day feeding trail, the results showed the specific growth rate (SGR) of larvae in E50, E100 and E200 group was significantly higher than that of control (p < 0.05). Furthermore, dietary emodin inclusion did not affect the SOD, CAT and GPx activity, while significantly decreased the MDA level (p < 0.05). Moreover, dietary emodin (50 mg·Kg−1) notably enhanced the expression of immune related genes including nrf2, il-1β, tgf-β, ifn-γ, ifn-i and irf3. Additionally, a higher relative abundance of Idiomarina and Halomonas, as well as a lower content of Mycoplasma was observed in E50 group, whereas Enterobacter content remarkably decreased in E200 group at genus level (p < 0.05). Finally, the M. salmoides larvae in E50 group exhibited a relative higher survival rate (p < 0.05), while larvae in E200 group showed a slightly higher mortality than that of control. Collectively, these results demonstrated that proper dosage of supplementing emodin (50 mg·Kg−1) in diet could lead to a promotion of growth performance, immunity, and a protective effect on M. salmoides larvae against MSRV infection.

Low-frequency band noise generated by industrial recirculating aquaculture systems exhibits a greater impact on Micropterus salmoidess

The effect of underwater noise environment generated by equipment in industrial recirculating aquaculture systems (RAS) on fish is evident. However, different equipment generate noise in various frequency ranges. Understanding the effects of different frequency ranges noise on cultured species is important for optimizing the underwater acoustic environment in RAS. Given this, the effects of underwater noise across various frequency bands in RAS on the growth, physiology, and collective behavior of juvenile largemouth bass (Micropterus salmoides) were comprehensively evaluated here. In this study, three control groups were established: low-frequency noise group (80–1000 Hz, 117 dB re 1μPa RMS), high-frequency noise group (1–19 kHz, 117 dB re 1μPa RMS), and ambient group. During a 30-day experiment, it was found that: 1) industrial RAS noise with different frequency bands all had a certain inhibitory effect on the growth of fish, which the weight gain rate and product of length and depth of caudal peduncle in the ambient group were significantly higher than those of the two noise groups, with the low-frequency noise group showing significantly lower values than the high-frequency noise group; 2) industrial RAS noise had a certain degree of adverse effect on the digestive ability of fish, with the low-frequency noise group being more affected; 3) industrial RAS noise affected the collective feeding behavior of fish, with the collective feeding signal propagation efficiency and feeding intensity of the noise groups being significantly lower than those of the ambient group, and the high-frequency noise group performing better than the low-frequency noise group as a whole therein. From the above, the underwater noise across different frequency bands generated by equipment operation in industrial RAS both had an impact on juvenile largemouth bass, with the low-frequency noise group being more severely affected.

Effects of Ala-Gln on growth, biochemical indicators and stress-related gene expression of largemouth bass (Micropterus salmoides) under dual stress of flow rate and density

The experiment focused on the study aimed to investigate the effects of adding alanyl-glutamine (Ala-Gln) to the feed on the growth, serum biochemical parameters, and the mRNA expression levels of stress-related genes in largemouth bass (Micropterus salmoides) under dual stress conditions of density and flow rate. The fish were divided into three groups: control group, dual stress group and dual stress with 0.9 % Ala-Gln addition group, and underwent a 60 day aquaculture experiment. The data showed that final weight, average weight gain rate, specific growth rate and feed efficiency of largemouth bass significantly decreased under dual stress (P < 0.05). At the same time, the levels of glucose and malondialdehyde (MAD), the activities of aspartate aminotransferase (AST) and alanine transaminase (ALT) in serum increased significantly under dual stress, while the total antioxidant capacity and serum lysozyme activity decreased significantly (P < 0.05). Moreover, the mRNA expression of growth hormone (GH), insulin-like growth factor-Ⅰ(IGF-I), nuclear factor kappa-B (NF-κB), interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), interleukin-8 (IL-8), nuclear transcription factor E2 related factor 2 (Nrf2), catalase (CAT), superoxide dismutase (SOD), Caspase 3, Caspase 8 and B-cell lymphoma-2 (Bcl2) genes all decreased significantly, the mRNA expression of HSP 70, HSP 90, interleukin-10 (IL-10), I-kappa-B-alpha (IkBα), kelch-1ike ECH- associated protein 1 (Keap1) and bcl2-associated X (Bax) genes all increased significantly (P < 0.05). However, the growth performance, serum biochemical indexes and mRNA expression of most genes in largemouth bass showed a correction trend after Ala-Gln addition, but still did not reach the level of control group. These results showed that dual stress of density and flow rate reduced growth and serum biochemical parameters in largemouth bass and increased the adverse expression of stress-related genes, while exogenous addition of Ala-Glu could somewhat ameliorate the negative effects of dual stress on largemouth bass.

Effects of dietary phytosterol on growth, lipid homeostasis and lipidomics of largemouth bass (Micropterus salmoides)

Little information is available on how exogenous phytosterol (PS) affect the growth performance and lipid homeostasis in fish. In the present study, an 8-week feeding trial were used to investigate the effects of PS on growth performance, serum biochemical indexes, cholesterol (CHO) metabolism and lipidomics of juvenile largemouth bass (Micropterus salmoides). The treatment diets (PS1-PS5) were formulated with supplementation of 0.01 %, 0.02 %, 0.03 %, 0.04 %, and 0.05 % PS on basis of the control diet (C, crude protein 48.39 %, crude lipid 11.65 %). Results showed that the final body weight and specific growth rate of largemouth bass increased as the levels of PS addition increased, reaching stability in the PS3 group. The concentration of high-density lipoprotein cholesterol was elevated and low-density lipoprotein cholesterol was reduced in serum were elevated following PS intervention at 0.03 %. PS treatment reduced the expression of genes associated with endogenous CHO anabolism, while increasing CHO catabolism and suppressing the corresponding negative transcriptional regulators. Lipidomics results showed that the composition patterns of lipid classes between the C and PS4 groups were similar. 7 of triglyceride (TG), 5 of phosphatidylcholine (PC), 2 of PE (phosphatidylethanolamine) and 1 of DG (diglyceride) lipid moleculars were identified as the potential lipid biomarkers in PS4 group. Furthermore, PS4 treatment enriched the pathway of ‘membrane component’ and ‘polyunsaturated fatty acid’. In conclusion, lipid and cholesterol metabolism were altered by the PS treatment, and the appropriate PS addition level was found to be 0.03 % based on the growth performance of the largemouth bass.

Dietary sodium butyrate positively modulated intestinal microbial community, but did not promote growth of largemouth bass (Micropterus salmoides).

This study investigated the effects of dietary sodium butyrate (NaB) on growth, serum biochemical indices, intestine histology, and gut microbiota of largemouth bass (Micropterus salmoides). A basal diet was formulated and used as the control diet (Con), and five additional diets were prepared by supplementing NaB (50%) in the basal diet at 2.0, 4.0, 8.0, 12.0, and 16.0 g/kg inclusion (NaB-2, NaB-4, NaB-8, NaB-12, and NaB-16 diets). Then, the six diets were fed to triplicate groups of largemouth bass juveniles (2.4 ± 0.1 g) for 8 weeks. NaB supplementation linearly and quadratically affected weight gain (WG) and feed intake (FI) (P < 0.05). The NaB-16 group displayed lower WG (- 6.8%) and FI than the Con group (P < 0.05), while no differences were found in WG and feed conversion ratio between the other NaB groups and Con group (P > 0.05). Serum alkaline phosphatase and lysozyme activities were higher in the NaB groups (P < 0.05), and D-lactate content was lower in the NaB-12 group (P < 0.05) than the control. Intestinal lipase activity in NaB-2, NaB-4 group, and villi width in NaB-8 group were also higher than those in the Con group (P < 0.05). Compared to the Con group, the intestinal abundances of Firmicutes and Mycoplasma were increased and the abundances of Proteobacteria, Achromobacter and Plesiomonas were decreased in NaB-4 and NaB-16 groups (P < 0.05). In conclusion, dietary NaB did not promote the growth of juvenile largemouth bass, but positively modulated the intestinal microbial community.

Effects of Lactobacillus plantarum and Bacillus subtilis on growth, immunity and intestinal flora of largemouth bass(Micropterus salmoides)

Probiotics play a crucial role in largemouth bass aquaculture, primarily in enhancing water quality, preventing fish diseases, promoting largemouth bass growth, and boosting immunity in high-density culture conditions. The experiment was actualized by adding Lactobacillus plantarum, Bacillus subtilis and a mixture of probiotic (L. plantarum and B. subtilis 1:1) in the culture water of largemouth bass for 42 days, respectively, to explore the effect of the above two probiotics on the growth performance and immunity ability of largemouth bass (Micropterus salmoides).Results: At the level of phylum, the relative abundance of enteric flora in Tenericutes of largemouth bass in L. plantarum added group was significantly higher than that in control group (p < 0.05). Conversely, the relative abundance of Proteobacteria was significantly lower than that of control group (p < 0.05). Similarly, at the genus level, the relative abundance of Mycoplasma and Leifsonia was significantly higher than that of control group (p < 0.05), while the relative abundance of Aeromonas was significantly lower in the L. plantarum added group compared to the control group (p < 0.05). Compared with the control group, there were no significant differences in phylum level in the B. subtilis added group (p < 0.05), and the relative abundance of Plesiomonas was significantly increased (p < 0.05), the relative abundance of Aeromonas was significantly decreased at genus level (p < 0.05). The relative abundance of Plesiomonas and Parabacteroides in the mixed probiotic treatment group was significantly increased (p < 0.05), the relative abundance of Aeromonas was significantly decreased at the level of genus (p < 0.05). The metabolites of carboxylic acid and its derivatives, organic oxygen compound, glycerophospholipid, lip acyl and other categories in enteric tissues of all treatment groups had significant changes (p < 0.05), enteric bacterial secondary metabolites such as SCFAs and 1-Phosphatidyl-D-myo-inositol were significantly increased (p < 0.05). The results showed that the addition of L. plantarum and B. subtilis in water could promote the growth of largemouth bass and increase its nonspecific immunity by enhancing the stability of enteric flora, increasing efficiency of enteric digestion and absorption and promoting the anti-inflammatory and immune ability of the body through secondary metabolites of enteric microbe.

Improving the Aerobic Capacity in Fingerlings of European Sea Bass (Dicentrarchus labrax) through Moderate and Sustained Exercise: A Metabolic Approach.

Sustained swimming induces beneficial effects on growth and energy metabolism in some fish species. However, the absence of a standardized exercise regimen that guarantees an optimal response to physical activity is due to the anatomical, behavioral, and physiological differences among species, and the different conditions of tests applied, which are especially notable for the early stages of cultured species. The objective of this study was to assess the growth and metabolic responses of European sea bass submitted to continuous and moderate exercise exposure, selecting a practical swimming speed from swimming tests of groups of five fingerlings. The exercise-effects trial was carried out with 600 sea bass fingerlings (3-5 g body weight) distributed in two groups (control: voluntary swimming; exercised: under sustained swimming at 1.5 body lengths·s-1). After 6 weeks, growth parameters and proximal composition of both muscles were not altered by sustained swimming, but an increased synthetic capacity (increased RNA/DNA ratio) and more efficient use of proteins (decreased ΔN15) were observed in white muscle. The gene expression of mitochondrial proteins in white and red muscle was not affected by exercise, except for ucp3, which increased. The increase of UCP3 and Cox4 protein expression, as well as the higher COX/CS ratio of enzyme activity in white muscle, pointed out an enhanced oxidative capacity in this tissue during sustained swimming. In the protein expression of red muscle, only CS increased. All these metabolic adaptations to sustained exercise were also reflected in an enhanced maximum metabolic rate (MMR) with higher aerobic scope (AMS) of exercised fish in comparison to the non-trained fish, during a swimming test. These results demonstrated that moderate sustained swimming applied to sea bass fingerlings can improve the physical fitness of individuals through the enhancement of their aerobic capacities.

Effects of replacing fishmeal with different proportions of mixed protein source in the diet of largemouth bass (Micropterus salmoides)

Fishmeal is an important protein source for largemouth bass (Micropterus salmoides). However, the production of fishmeal is decreasing each year and the price of fishmeal is rising. Therefore, it is necessary to find new high-quality and suitable protein sources. This study used a mixed animal protein source (chicken meal:blood meal:shrimp meal:brewer's yeast = 50:12.5:25:12.5) to replace fishmeal. Using a 48 % fishmeal group as the control, five diets with different fishmeal levels (FM48, FM44, FM40, FM36, FM32) were established to determine the effects on largemouth bass growth performance, liver health and intestinal health. There were no significant differences in the percentage weight gain, specific growth rate, feed conversion rate, and condition factor of largemouth bass, but the hepatosomatic and viscerosomatic indexes were significantly decreased when the dietary fishmeal level was reduced to 40 %. The content of taurine, glycine, and histidine was significantly reduced in the muscle of largemouth bass fed the FM32 diet compared with those fed the FM48 and FM44 diets. Mixed protein feed reduced the total bile acid content and increased the low-density lipoprotein cholesterol content in the plasma of largemouth bass. The replacement of fishmeal with the mixed protein source inhibited the expression of tnf-α and caspase 3 and enhanced the expression of apoa1 in the liver, as well as enhancing the protein expression of FXR and SREBP and inhibiting the protein expression of P-PPARA in the liver. The intestinal pparα expression was suppressed when dietary fishmeal was replaced. When dietary fishmeal decreased, the mucosal folds height and muscle layer thickness also decreased. In conclusion, partial replacement of fishmeal with the mixed protein source did not affect the growth performance, while lipid metabolism and intestinal health were negatively affected when dietary fishmeal levels were below 36 %.

Different Starch Sources Affect the Growth Performance and Hepatic Health Status of Largemouth Bass (Micropterus salmoides) in a High-Temperature Environment.

The experiment was designed to investigate the effects of different starch types on the growth performance and liver health status of largemouth bass in a high-temperature environment (33-35 °C). In this study, we designed five diets using corn starch (CS), tapioca starch (TS), sweet potato starch (SPS), potato starch (PS), and wheat starch (WS) as the starch sources (10%). We selected 225 healthy and uniformly sized largemouth bass (199.6 ± 0.43 g) and conducted the feeding experiment for 45 days. The results showed that the WS group had the highest WGR, SGR, and SR and the lowest FCR. Among the five groups, the WS group had the highest CAT activity, SOD activity, and GSH content, while the SPS group had the highest MDA content. Furthermore, oil red O staining of liver samples showed that the TS group had the largest positive region, indicating high lipid accumulation. Lastly, the gene expression results revealed that compared with the WS group, the CS, TS, and SPS groups showed suppressed expression of nrf2, keap1, cat, sod, gpx, il-8, and il-10. Therefore, our results demonstrated the effect of different starch sources on largemouth bass growth performance and hepatic health in a high-temperature environment.

Effects of dietary citrus pulp level on the growth and intestinal health of largemouth bass (Micropterus salmoides).

Citrus pulp (CP) is rich in pectin, and studies have shown that pectin possesses antioxidant, anti-inflammatory, and gut microbiota-regulating properties. However, the application of CP in aquafeed is limited. In this study, the effect of dietary inclusion of CP on the intestinal health of largemouth bass (Micropterus salmoides) was investigated. Juveniles of similar size (6.95 ± 0.07 g) were fed isonitrogenous and isoenergetic diets containing different levels of CP (0%, 3%, 6%, 9%, 12%, or 15%) for 58 days. As the level of CP in the feed for largemouth bass increased, the fish's growth performance and intestinal health initially improved and then declined. Adding low doses of CP (≤9%) to the feed had no significant impact on the growth performance of large-mouth black bass, whereas high doses of CP (>9%) significantly reduced their growth performance. Adding 6%, 9%, or 12% of CP to that feed enhanced the expression of genes related to tight junctions, anti-inflammatory activity, anti-apoptotic activity, and antioxidant activity in the intestines of largemouth bass. It reduced intestinal inflammation and improved intestinal nutrient absorption, intestinal mucosal barrier function, and intestinal antioxidant capacity. Moreover, it improved the α-diversity, structure, and function of the intestinal flora. The addition of 6% CP had the most beneficial effect on the intestinal health of largemouth bass. On the other hand, the addition of 15% CP had adverse effects on the intestinal antioxidant capacity and intestinal mucosal barrier function of largemouth bass. Adding 6-9% CP to the feed for largemouth bass can improve their intestinal health without having a significant impact on their growth performance. CP could serve as a novel prebiotic and immunostimulant ingredient in aquafeed. © 2023 Society of Chemical Industry.

The effects of enrofloxacin exposure on responses to oxidative stress, intestinal structure and intestinal microbiome community of largemouth bass (Micropterus salmoides)

Antibiotic residues in the aquaculture environments may lead to antibiotic resistance, and potentially exert adverse effects on health of the non-target organisms and humans. In order to evaluate the effect of enrofloxacin of environmental concentrations on largemouth bass (Micropterus salmoides). Two hundred and seventy largemouth basses (with an average weight of 7.88 ± 0.60 g) were randomly divided into three groups, and separately exposed to 0, 1, 100 μg/L enrofloxacin (Control, ENR1, ENR100) for 30 days to detect the effect of enrofloxacin on the growth performance, oxidative stress, intestinal microbiota structure, inflammatory response and structure of the intestine. The results showed that ENR significantly reduced the final body weight (FBW) and weight gain rate (WGR), and increased feed conversion ratio (FCR) (P < 0.05). The histopathological analysis revealed that the villus width and muscular thickness of anterior intestine were significantly decreased with the increasing of enrofloxacin concentration. The activity of SOD was significantly increased at enrofloxacin stress, while CAT and POD activity were significantly decreased compared to control group (P < 0.05). The activities of lysozyme (LZM), alkaline phosphatase (AKP) and peroxidase (POD) in ENR1 was higher than that of control and ENR100 groups. Enrofloxacin treatment up-regulated the expression IL-1β and TNF-α, and down-regulated IL-10, and decreasing the expression level ZO-1, claudin-1, and occludin. Furthermore, the enrofloxacin treatment significantly decreased the intestinal bacterial diversity (P < 0.05). Exposure to 100 μg/L enrofloxacin obviously increased the relative abundance of Bacteroidota, Myxococcota, and Zixibacteria of fish gut, and reduced Firmicutes; 1 μg/L enrofloxacin considerably increased Bacteroidota, Myxococcota, and Actinobacteria, and reduced Firmicutes. The relative abundance of DTB120 and Elusimicrobiota was positively correlated with the occludin and claudin-1 gene. Taken together, exposure to enrofloxacin inhibited the growth of largemouth bass, influenced intestinal health, and induced dysbiosis of the intestinal microbiota.

Transcriptomic Comparison of Liver Tissue across Different Largemouth Bass (Micropterus salmoides) Strains

Over the past few years, China has become a hotspot for the domestication of the commercially valuable largemouth bass (Micropterus salmoides). Although the food preference of this fish has been studied, little is known about the genes regulating its growth. Population breeding was performed using two indigenous strains (QT1 and QT2), with the results showing that the organ/body ratio, abdominal fat rate and the body weight gain of QT1 and QT2 were higher than for the offspring YL1 and Y3 which are extensively cultured in China. Subsequent RNA sequencing (RNA-Seq) allowed for the identification of potential genes and pathways involved in growth performance. Overall, the transcriptome analysis generated 89,056 transcripts and 42,529 Unigenes. A PCA revealed significant differences between QT1 and the other three strains, while the other three strains did not show much difference. A KEGG enrichment analysis of differentially expressed genes showed that steroid biosynthesis was the most enriched pathway among the four strains. These pathways could be related to the growth of largemouth bass. In addition, a co-expression network analysis suggested a strong interaction between liver steroid biosynthesis and the genes for photosynthesis, secondary metabolism and stress response. Taken together, the above results can provide new insights into the liver metabolism of different strains of largemouth bass during culture and provide references for the subsequent domestication and breeding programs of largemouth bass.

Effects of different stocking densities and feeding frequencies on growth, physiological and biochemical indexes, and intestinal microflora of largemouth bass (Micropterus salmoides) under land-based round pond

Land-based Round Pond is an emerging and efficient aquaculture technique widely adopted in Southwest China. To study the effects of stocking density and feeding frequency on growth, oxidative stress, physiological characteristics, and intestinal flora of largemouth bass (Micropterus salmoides) in Land-Based Round Pond, 3 × 2 two-factor treatment groups were set with three stocking densities (30, 40, and 50 fish/m3) and two feeding frequencies (2 and 3 times/day). Largemouth bass (initial weight of 155.62 ± 2.43 g) were stocked for 60 days. The yield of 30 fish/m3 groups were close to 40 fish/m3 groups, but the 30 fish/m3 groups demonstrated significantly higher growth rate, condition factor and lipid content compared to other density groups with a lower feed conversion ratio (p < 0.05). The feeding frequency of 3 times per day resulted in higher growth rate than 2 times per day with a higher feed conversion ratio (p < 0.05). Physiological and biochemical analyses showed that levels of TC, TG, lysozyme, ALP, T-SOD, CAT, AOC, lipase, and trypsin were significantly higher in the 30 fish/m3 groups than those of other density groups, while MDA content were highest in the 50 fish/m3 groups than other groups (p < 0.05). The T-SOD and CAT activity were significantly higher in the 3 times per day groups than those in the 2 times per day groups (p < 0.05), and no significant effect of feeding frequency on the immunity was observed. No pathological changes were found in muscle and intestinal histology, but infiltration of hemocytes was found in liver in the 50 fish/m3 groups. In intestinal microbial analysis, the 40 and 50 fish/m3 density groups had a higher relative abundance of Proteobacteria, suggesting a higher probability of disease occurrence and an unstable intestinal microflora. These results demonstrate that the optimal stocking density for largemouth bass in Land-Based Round Ponds is 30 fish/m3 (155 g/fish) at a size stage ranging from 155.62 g to 353.83 g, with the optimal feeding frequency of 3 times per day. This study provides a theoretical basis for the development of Land-Based Round Ponds.

Optimal dietary zinc inclusion improved growth performance, serum antioxidant capacity, immune status, and liver lipid and glucose metabolism of largemouth bass (Micropterus salmoides)

This study was conducted to ascertain the effect of dietary Zn on growth and health status of juvenile largemouth bass (Micropterus salmoides). Six experimental diets with Zn level of 50.17, 56.74, 73.34, 86.03, 123.94, and 209.20 mg/kg, respectively were compounded using complex amino acid-chelated zinc, and were fed to juvenile fish (5.50 ± 0.10 g) for 70 d. The specific growth rate (SGR) varied with dietary Zn level in a quadratic model and peaked at the 73.34 mg/kg group, while the feeding rate exhibited an opposite trend (P < 0.05). The condition factor, hepatosomatic index and mesenteric fat index all exhibited a tendency similar with SGR (P < 0.05). Dietary Zn level affected serum total proteins, urea, triglycerides, and glucose (P < 0.05). Serum Zn and copper levels linearly increased with dietary Zn level, while serum iron and manganese showed the opposite trend. Serum superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) increased with dietary Zn level and reached a plateau at 86.03 mg/kg. Serum complement component 3 (C3), IgM, and lysozyme also were enhanced by 73.34 mg/kg Zn. Body protein content increased with zinc level up to 73.34 mg/kg, and then remained steadily. As dietary Zn level increased, hepatic lipid level increased and then reached a plateau at 86.03 mg/kg group, while glycogen increased linearly. Moreover, gene expression related to lipid and glycogen metabolism from liver transcriptome further explained the liver lipid and glycogen variations. To conclude, a dietary Zn requirement of 76.99 mg/kg was suggested for juvenile largemouth bass to improve growth, antioxidant capacity, and immune status.

Dietary calcium β-hydroxy-β-methylbutyrate supplementation improved the flesh quality, but did not promote the growth performance of largemouth bass (Micropterus salmoides)

β-hydroxy-β-methylbutyric acid (HMB) is an intermediate product of leucine metabolism, which can promote protein synthesis. The study explored the dietary effects of HMB on the growth, muscle composition, flesh textural characteristics and flesh quality-related genes expression of largemouth bass (Micropterus salmoides). Calcium β-hydroxy-β-methylbutyrate (HMB-Ca) was supplemented to the control diet at levels of 0.5 (HMB-0.5) and 1g/kg (HMB-1), to form three iso-nitrogenous diets. Then, 108 largemouth bass with average body weight of (110.0 ± 0.1) g were divided into 3 groups with three replicates per group and 12 fish per replicate to feed the above three diets for 12 weeks. No significant difference was observed in weight gain, feed conversion ratio as well as viscerosomatic index, condition factor and intraperitoneal fat ratio among the three treatments (P<0.05). Compared with the control group, muscle crude lipid, n-3 PUFA content and n-3/n-6 ratio were raised in both HBM-Ca groups, and crude protein, collagen content, non-essential and total amino acids in flesh were promoted only in HMB-0.5 group. The addition of 0.5 and 1g/kg HMB-Ca in diets enhanced flesh yellowness and decreased lightness (P<0.05). In terms of flesh textural properties, the hardness, springiness, chewiness and shear force in the HMB-0.5group were higher than those of the control group (P<0.05). In addition, the supplementation of 0.5g/kg HMB-Ca significantly lowered muscle fiber diameter and elevated muscle fiber density (P<0.05). In gene expression, the mRNA levels of 4E-BP1, FoxO3a, MuRF-1, Atrogin-1 and MSTN were significantly lower, and S6K1, MyoD, MyOG, Myf5 and Myf6 were higher in the HMB-0.5 group than those of the control group (P<0.05). Moreover, the expression levels of PI3K, AKT and TOR mRNA were also up-regulated in both HMB-Ca groups (P<0.05). Overall, dietary HMB-Ca supplementation did not promote the growth of large-size largemouth bass, but improved muscle nutritional composition and flesh texture, partially attributing to the combined effect of AKT/TOR-FoxO3a signaling pathway and myogenic regulatory factors. The optimal content of HMB-Ca supplementation for largemouth bass was recommended to be 0.5 g/kg.

Dietary effects of supplementing Clostridium butyricum culture or sodium butyrate in low fishmeal diet on growth, serum indicators, intestinal histology and microbiota of largemouth bass (Micropterus salmoides)

The present study aimed to evaluate the dietary effects of Clostridium butyricum culture (CC) or sodium butyrate (SB) on the growth, feed utilization, serum indicators, intestinal histology and microbiota of largemouth bass (Micropterus salmoides). CC and coated SB (50%) were supplemented to a low fish meal diet (245 g/kg) (control diet) at the inclusion levels of 1 g/kg and 2 g/kg, to form five iso-nitrogenous and iso-lipidic diets (control, CC-1, CC-2, SB-1, and SB-2). Then, the five diets were fed to largemouth bass with initial body weight of 70.2 ± 0.1 g. After 8 weeks of feeding, dietary supplementation of 1 g/kg CC increased the weight gain (WG) by 7.4% (P < 0.05), and decreased the feed conversion ratio by 0.09 (P < 0.05), while dietary SB just numerically improved the WG (P > 0.05), when compared to the control. The muscle composition was not significantly affected by the inclusion of CC or SB (P > 0.05). Dietary inclusion of CC or SB significantly reduced serum diamine oxidase activity and increased lysozyme activity (P < 0.05), while the decreased D-lactic acid level was observed only in the two SB groups (P < 0.05). In intestinal histology, the 1.0 g/kg CC group presented significantly higher intestinal villus height, width and muscle layer thickness than the control group (P < 0.05). The intestinal microbiota analysis showed that dietary CC or SB (1 g/kg) increased the abundance of Fusobacteriota and Cetobacterium, decreased the abundance of Proteobacteria and Aeromonas. In conclusion, the supplementation of CC in low fish meal diet promoted the growth performance, feed utilization, and both CC and SB supplementation positively modulated the intestinal microorganism community of largemouth bass.

Role of dietary isoleucine supplementation in facilitating growth performance and muscle growth in juvenile largemouth bass (Micropterus salmoides)

To improve the breeding efficient of fish, it is crucial to provided essential nutrients based on the nutritional demands. Isoleucine is an essential amino acid, and it plays a significant role in growth and metabolism of largemouth bass. Therefore, this study aimed to investigate the effects of dietary isoleucine on the growth and muscle development of largemouth bass (Micropterus salmoides) by conducting an 8-week feeding experiment. Fish (initial weight 19.97 ± 0.04 g) were randomly distributed into six treatments with three replicate groups of 20 fish and fish were fed diets with varying isoleucine levels (1.47%, 1.68%, 1.93%, 2.30%, 2.46%, and 2.72% of dry diet). Results revealed that isoleucine supplementation increased the specific growth rate (SGR) and significantly decreased the feed conversion ratio (FCR). Moreover, histological analysis of the muscle tissue revealed a significant correlation between the size and density of muscle fibers and isoleucine levels. This alteration may be attributed to the downregulation of myostatin and muscle growth-related genes, MyoD and MyoG, respectively. Additionally, fish fed an isoleucine-supplemented diet showed downregulated expression of apoptosis-related (Caspase-3, Caspase-8, and Caspase-9) and ubiquitin-proteasome pathway-related (Ub, Murf1, Mafbx, and Psmc1) genes (1.93%−2.30%). The muscle and plasma total protein contents showed similar patterns of variation to the gene described above. Furthermore, isoleucine supplementation significantly increased body protein levels and decreased body lipid levels. Quadratic regression analysis revealed that the optimal isoleucine levels for juvenile largemouth bass were 1.997% and 1.837% in the dry diet (4.21% and 3.87% of dietary protein) for SGR and FCR, respectively.