Largemouth Research Articles

Hypoxia induces reversible gill remodeling in largemouth bass (Micropterus salmoides) through integrins-mediated cell adhesion

Gill remodeling is an important strategy for fish to cope with hypoxia, and many of the teleost possess this ability, but the underlying mechanism is not well understood. To investigate the mechanism of hypoxia-induced gill remodeling, largemouth bass (Micropterus salmoides) exposed to hypoxia (dissolved oxygen level: 2.0 ± 0.2 mg L−1) for 7 days, followed by 7 days of reoxygenation. Hypoxia tests were also performed on primary gill cells from largemouth bass. We found that hypoxia-induced gill remodeling increased the respiratory surface area of the gills. This change in gill morphology was reversible and recovered after reoxygenation. A reduction in the number of mucous cells and rearrangement of mitochondria-rich cells (MRCs) were observed during gill remodeling. After 7 days of reoxygenation, the number of mucous cells and the position of the MRCs were restored. Hypoxia resulted in a 2.92-fold increase in the number of primary gill cells that underwent migration over a 12-h period. The mRNA levels of nine integrin subunits (α1, α2, α5, α7, α8, α10, αL, β1 and β2) were significantly up-regulated after 12 h of hypoxia in vivo, and the changes in the expression of these subunits were consistent with the HIF-1α trend. Immunohistochemistry showed that integrin β1 protein levels were significantly increased and were abundantly expressed in the interlamellar cell mass after exposure to hypoxia. Taken together, the results of the present study demonstrated that changes in mucosal cells and MRCs play an important role in hypoxia-induced gill remodeling in largemouth bass and that these changes are regulated by integrins.

Condensed tannin improves growth and alleviates intestinal inflammation of juvenile largemouth bass (Micropterus salmoides) fed with high cottonseed protein concentrate diet

The objective of this study was to examine the potential of condensed tannin (CT) in mitigating the adverse effects on growth and intestinal health induced by high cottonseed concentrate protein (CPC) diets in juvenile largemouth bass (Micropterus salmoides). Largemouth bass were respectively fed with the basic diet, the high CPC diet, and the CPC + CT diet (incorporated 3.75 g/kg CT into the high CPC diet) for a duration of 8 weeks. Results indicated that the high CPC diet resulted in decreased growth performance and compromised intestinal health. Dietary CT enhanced the growth of fish, improved intestinal function, and optimized intestinal microbiota. Additionally, intestinal transcriptome analysis revealed that dietary CT might mitigate intestinal inflammation by downregulating the related gene expression in the cell adhesion molecule pathway. Furthermore, the gene expression of cd22 and mhc2 was positively correlated with the relative abundance of the Geodermatophilus, an indicator species of intestinal microbiota in high CPC treatment. Our research suggests that the inclusion of CT (3.75 g/kg) in the high CPC diet of largemouth bass can stimulate growth and alleviate negative impacts on intestinal health, indicating that CT can be utilized to enhance the utilization of CPC in fish nutrition.

Interactions between feed protein source and feeding frequency on growth performance and health status of largemouth bass (Micropterus salmoides).

In order to evaluate the effects of the interaction between different proteins and feeding frequency on largemouth bass (Micropterus salmoides) and to provide scientific guidance for the application of novel proteins and the corresponding optimal feeding strategy, a two-factorial design (5 × 3) with five protein feeds (fishmeal (FM), Clostridium autoethanogenum protein (CAP), Tenebrio molitor (TM), Chlorella meal (ChM), cottonseed protein concentrate (CPC)), and three feeding frequency (1, 2, and 3 times/d; FF1, FF2, FF3) was designed in culturing largemouth bass (initial weight, 2.98 ± 0.22g/fish) for 8weeks. Z-score combined with cluster analysis was used to analyze and compare the effects of different treatments on different indicators, such as growth performance, feed utilization, antioxidant capacity, and immune response to draw a general picture of the relationship among all these massive biomarkers. The results showed that different protein sources and feeding frequencies had significant interactive effects on growth performance, feed utilization efficiency, body lipid, and health status of largemouth bass. Fish fed with ChM feed showed similar performance to that in FM group, implying its potential for complete replacement of fishmeal in largemouth bass. Fish fed with CAP, TM, and CPC feeds showed worse performance compared to FM and ChM groups, characterized by poor growth and feed utilization, enhanced stress, chronic inflammation, and varying symptoms of histological changes in the liver and intestine, which demonstrated the adverse effects of the complete replacement of fishmeal by these three proteins. In terms of feeding frequency, fish fed with FM feed in FF3 group led to liver hypertrophy, fat accumulation, and the risk of fatty liver, while inducing liver inflammation. In addition, the TM and CAP group had the higher expression levels of inflammatory factors at FF3 group, which displayed that the interactions between FM, CAP, TM feeds and feeding frequency at FF3 might aggravate the occurrence of liver inflammation and oxidative damage of hepatocytes. Overall, FF2 had higher feed efficiency, protein efficiency, antioxidant enzyme and lysozyme activities, lower MDA content, and lower gene expression of inflammatory cytokines and could be considered as the optimum feeding frequency for largemouth bass fed with different protein feeds.

Astaxanthin attenuates glucose-induced liver injury in largemouth bass: role of p38MAPK and PI3K/Akt signaling pathways

BackgroundAstaxanthin (ASX) has been documented to exert beneficial influence on various processes in fish. Largemouth bass (Micropterus salmoides) serves as a common model for studying glucose-induced liver disease, making it imperative to investigate the regulatory mechanisms underlying its liver health.MethodsLargemouth bass were fed with a control diet (CON), a high carbohydrate diet (HC), or a HC diet supplemented astaxanthin (HCA) for 8-weeks, followed by the glucose tolerance test (GTT). Primary hepatocytes were treated with low glucose and high glucose combined with different concentrations of astaxanthin for 48 h. The histopathology, enzymology, transcriptomics, molecular biology and cell biology were combined to investigate the mechanism of liver injury.ResultsThis study provides evidence for the protective effects of ASX against growth performance reduction and hepatic liver injure in largemouth bass fed HC diet. In GTT, HCA diet exhibited an improvement in glucose tolerance following glucose loading. Although HCA diet did not restore the expression of insulin resistance-related genes in livers at different time during the GTT, the addition of ASX in the long-term HC diet did improve the insulin resistance pathway by regulating the PTP1B/PI3K/Akt signaling pathway. Hepatic transcriptome analyses showed that ASX plays an essential role in the modulation of glucose homeostasis in response to treated with HC diet. In in vitro study, ASX treatment resulted in an exaltation in cell viability and a reduction in the rate of cell apoptosis and reactive oxygen species (ROS). Additionally, astaxanthin was observed to improve apoptosis induced by high-glucose via p38MAPK/bcl-2/caspase-3 signaling pathway.ConclusionsAstaxanthin exhibited a protective effect against apoptosis by regulating p38MAPK/bcl-2/caspase-3 pathway, and ameliorated insulin resistance by activating the PTP1B/PI3K/Akt pathway. This study elucidated the mechanism of astaxanthin in the liver injury of largemouth bass from a new perspective and provided a new target for the treatment of insulin resistance.Graphical

Genome-Wide Association Study of Resistance to Largemouth Bass Ranavirus (LMBV) in Micropterus salmoides.

The disease caused by Largemouth bass ranavirus (LMBV) is one of the most severe viral diseases in largemouth bass (Micropterus salmoides). It is crucial to evaluate the genetic resistance of largemouth bass to LMBV and develop markers for disease-resistance breeding. In this study, 100 individuals (45 resistant and 55 susceptible) were sequenced and evaluated for resistance to LMBV and a total of 2,579,770 variant sites (SNPs-single-nucleotide polymorphisms (SNPs) and insertions-deletions (InDels)) were identified. A total of 2348 SNPs-InDels and 1018 putative candidate genes associated with LMBV resistance were identified by genome-wide association analyses (GWAS). Furthermore, GO and KEGG analyses revealed that the 10 candidate genes (MHC II, p38 MAPK, AMPK, SGK1, FOXO3, FOXO6, S1PR1, IL7R, RBL2, and GADD45) were related to intestinal immune network for IgA production pathway and FoxO signaling pathway. The acquisition of candidate genes related to resistance will help to explore the molecular mechanism of resistance to LMBV in largemouth bass. The potential polymorphic markers identified in this study are important molecular markers for disease resistance breeding in largemouth bass.

Effects of 17α-methyltestosterone and letrozole on growth and gonadal development in largemouth bass (Micropterus salmodies).

In order to optimize the parameters for reversing masculinization and establish the techniques for sex induction of pseudo-males and creation of all-female fry in largemouth bass (Micropterus salmodies, LMB), 15-day-old LMB (1.00 ± 0.10cm in length, 0.10 ± 0.01g in weight) were fed a diet supplemented with either 17α-methyltestosterone (MT) or letrozole (LE) and their combination. The experimental groups were M20 (20mg/kg MT), L20 (20mg/kg LE) and M10L10 (10mg/kg MT and 10mg/kg LE). The control group, named C, was not feed MT or LE. After 60 days, exogenous hormone in the diets was stopped and the effects of MT and LE on growth, male ratio, and gonadal development in LMB were evaluated. At 12-month-old, blood and gonadal tissue samples were collected to measure sex steroid hormones levels, analyze expression levels of dmrt1 and cyp19a1a genes, as well as examine the gonads morphology. The results showed no significant differences in growth between the experimental groups and the control group after a 60-day feeding period with the formulated diet (p > 0.05). The sex reversal ratio of M20, L20, M10L10 were 95.00%, 80.00%, 76.47%, respectively. The gonadal tissue sections showed that the gonadal structure of masculinized fish morphologic resembled that of control male fish. At 12-month-old, the sex reversal ratio in M20, L20, M10L10 and C groups were 100%, 86.67%, 73.33% and 50.00%, respectively. The testicular of pseudo-male fish in the M20 group exhibited well-developed morphology similarities to that of the control group males. However, the testes of pseudo-male fish in the L20 and M10L10 groups were smaller size Estradiol (E2) levels in the experimental groups was significantly lower than those in the control group females (p < 0.05), while testosterone (T) levels were significantly higher than that of the control group (p < 0.05). Compared to the female fish in the control group, pseudo-male fish from all experimental groups showed significantly upregulated expression of dmrt1 (p < 0.05), and significantly downregulated expression of cyp19a1a (p < 0.05). Pseudo-males selected from group M20 exhibited a significantly higher proportion of female offspring (92.00%) compared to the control group (46.50%). In summary, 20mg/kg MT was the optimal inducing concentration.

Comparing effects of high starch diet or high lipid diet supplemented with different levels of zinc on intestinal barrier and microbe community in largemouth bass Micropterus salmoides

Zinc is essential for normal growth and reproduction in all animals and plays a crucial role in many biological processes. The present study aimed to compare the intervention effects of zinc on intestinal health in a high lipid diet or high starch diet. Seven iso-nitrogenous (∼520 g kg−1) diets were formulated containing a positive control diet (115 g kg−1 lipid + 115 g kg−1 starch + 20 mg kg−1 Zn), three high starch diets (HS, 166 g kg−1 starch) and three high lipid diets (HL, 182 g kg−1 lipid), with 0 (HS-LZn, HL-LZn), 20 (HS-MZn, HL-MZn) and 150 (HS-HZn, HL-HZn) mg kg−1 Zn being supplemented. High starch diet and high lipid diet promoted feed efficiency, as evidenced by the lower feed conversion ratio. Three-way factorial ANOVA analysis showed high starch diet (166 g kg−1) significantly decreased final body weight and weight gain compared to the normal starch level (115 g kg−1). Diamine oxidase in serum significantly increased in diets HS-LZn and HL-LZn. In addition, distal intestinal mucosal fold damage and inflammatory infiltration were observed in the HS-LZn, HS-HZn, HL-LZn and HL-HZn groups. Fish fed HL diets (HL-LZn, HL-MZn, HL-HZn) showed lower expressions of claudin 5 and claudin 34, and higher IgD and IgM. Diets HL-LZn and HL-MZn significantly up-regulated C4 and C7. Proinflammatory cytokines including il8, il1β and tnfα significantly up-regulated in diet HL-LZn, even higher than the HS-LZn. Intestinal microbial composition indicated the abundance of Cetobacterium in HL-LZn was significantly higher than the control and HL-MZn diets. Similarly, LEfSe showed that Cetobacterium (P = 0.039) significantly enriched in the HL-LZn group. This study clarified high energy diet induced intestinal damage, which can be alleviated by zinc.

A droplet digital PCR assay to detect Chinese rice-field eels rhabdovirus.

Chinese rice-field eels rhabdovirus (CrERV) causes haemorrhagic disease in Chinese rice-field eels (Monopterus albus), leading to significant mortality and economic losses. Sensitive detection of CrERV nucleic acids is essential to control the spread of this pathogen and to treat infected individuals. Herein, we developed an efficient and sensitive droplet digital PCR (ddPCR) method to rapidly detect and quantify CrERV. The ddPCR assay optimal conditions were an annealing temperature of 53°C, and primer and probe concentrations of 0.5 and 0.25 μM, respectively. The assay had a diagnostic sensitivity of 0.23 copies/μL, and was highly specific, showing no cross reactivity with other viruses (infectious haematopoietic necrosis virus, grass carp reovirus, spring viremia of carp virus, largemouth bass ranavirus, carp edema virus, Chinese giant salamander iridovirus, and white spot syndrome virus). Real-time quantitative PCR testing of 30 Chinese rice-field eels samples detected CrERV in 7 samples (23.3%), whereas ddPCR detected CrERV in 12 samples (40%), demonstrating its higher sensitivity. Thus, ddPCR represents an advanced method to absolutely quantify CrERV in infected fish with low virus concentrations, providing a valuable tool to manage the spread and impact of CrERV.

Assessing factors related to Walleye stocking success in the Midwestern United States

AbstractObjectiveThe objective of this study was to evaluate stocking success of Walleye Sander vitreus in lakes and reservoirs across the Midwestern United States to inform stocking practices for state agencies. Demand for Walleye stocking may increase if climate change limits the potential for natural recruitment in lakes. Consequently, the strategic distribution of Walleye stocking may maximize fishing opportunities.MethodsWe synthesized data from 2226 Walleye fry and fingerling stocking events on 653 lakes in the Midwestern United States and used random forest algorithms and mixed‐effects linear models to identify abiotic and biotic factors related to Walleye stocking success.ResultLatitude and year explained relatively little variation in stocking success compared to within‐lake variation. Relative abundance of Largemouth Bass Micropterus nigricans was an important indicator of Walleye stocking success for fry and fingerlings, with stocking success generally decreasing with increased bass abundance. There was an interaction between lake surface area and growing degree‐days, as large lakes (&gt;2500 ha) seemed to be more conducive to Walleye stocking success regardless of growing degree‐days. The models that we developed did not accurately predict exact levels of Walleye stocking success but were 92–94% accurate in predicting whether the stocking success of both fry and fingerlings would be at or above the 50th percentile.ConclusionThese findings may help to inform the management and stocking allocation of Walleye and suggest that future increases in Largemouth Bass abundance and growing degree‐days could limit the effectiveness of stocking in some lakes.

Inactivated LMBV vaccine with nano‑aluminum adjuvant provided immune protection in largemouth bass (Micropterus Salmoides)

Largemouth bass ranavirus (LMBV) has caused severe economic losses in largemouth bass (Micropterus salmoides) aquaculture. Vaccination is acknowledged as an efficient strategy to prevent viral diseases in fish. In this study, an inactivated virus vaccine with nano‑aluminum adjuvant was successfully developed to protect largemouth bass effectively against LMBV. LMBV was inactivated by formalin and mixed with nano‑aluminum adjuvant under moderate agitation. The nano‑aluminum hydroxide adjuvant showed a cuboidal structure under the scanning transmission electron microscope (STEM), scanning electron microscope (SEM), and transmission electron microscope (TEM), and LMBV antigen-adsorbing rate was 39.49 % superior to those of micro‑aluminum hydroxide and IMS1312 adjuvants. The results from both external and internal damage assessments indicated that the nano‑aluminum vaccine had good safety for Micropterus salmoides. The relative percentage of survival was 80 % with a booster immunization in largemouth bass. The expression levels of immune-related genes such as TNF-α, IFN, and IL-8 were significantly up-regulated in the spleen of fish immunized by nano‑aluminum adjuvant vaccine compared to those in inactivated LMBV and control groups. The neutralizing antibody in nano‑aluminum adjuvant vaccine group showed higher abundance and lasted for a longer period. Lymphocytes from the head kidney of largemouth bass in the nano‑aluminum adjuvant vaccine group showed stronger proliferation activity in vitro post-stimulation with ConA. Moreover, stronger migration of the dendritic cells was induced by the nano‑aluminum adjuvant vaccine. Collectively, our findings suggested that the inactivated LMBV vaccine with nano‑aluminum adjuvant could provide efficient protection for largemouth bass against LMBV infection. The nano‑aluminum adjuvant has potential application with inactivated viral vaccines in fish.

Establishment and characterization of a novel cell line derived from spotted sea bass Lateolabrax maculatus and its susceptibilities to iridoviruses

The spotted sea bass (Lateolabrax maculatus), which holds significant commercial value, is extensively cultivated in China, Japan, and Southeast Asian countries. This study reports the establishment and characterization of a novel continuous cell line, designated as LMK cells, derived from the kidney tissue of spotted sea bass, The LMK cell line, primarily composed of epithelial-like cells, has been successfully subcultured in Medium 199 supplemented with 10 % fetal bovine serum (FBS) for over 60 passages. Mitochondrial genome sequencing and cytochrome c oxidase subunit I gene amplification verified the origin of the LMK cells from L. maculatus, distinguishing them from L. japonicus. Optimal culture conditions for LMK cells at passage 35 were determined to be 10 % FBS at 27 °C. Chromosomal analysis indicated that the cell line possesses 48 chromosomes. To assess viral susceptibility, LMK cells were exposed to the red sea bream iridovirus and largemouth bass ranavirus. Both iridoviruses induced cytopathic effects within 3 days post-infection and triggered immune-related gene responses. This study demonstrates that the LMK cell line is a valuable resource for molecular, virological, and immunological research in L.maculatus and other sea bass species.

Dietary condensed tannin supplementation improves growth performance and feed utilization of juvenile Largemouth bass (Micropterus salmoides) through positively regulating serum lipids and intestinal health

Considering the diverse biological activities of condensed tannin (CT), the study aimed to evaluate the effect of CT on growth performance and intestinal health in juvenile largemouth bass (Micropterus salmoides) through a 56-day feeding trial. Largemouth bass (5.99 ± 0.03 g) were fed a basic diet supplemented with different levels of CT: 0 g/kg (the control group, CG), 0.60 g/kg (the T0.6 group), 1.50 g/kg (the T1.5 group), 3.75 g/kg (the T3.75 group), and 9.38 g/kg (the T9.38 group). The results indicated that dietary supplementation of CT at 3.75 g/kg promoted growth performance, feed conversion ratio, the apparent digestibility coefficients (ADCs) of crude protein and crude lipid, the crude protein of whole-body, the intestinal antioxidant capacity, and intestinal immune response, as well as the development of intestinal villi (P < 0.05), while the fish fed with 9.38 g/kg CT exhibited the opposite trend. Further, dietary CT (3.75 g/kg) decreased crude lipid in the whole-body compared to the CG (P < 0.05). Dietary CT (3.75 g/kg) altered the microbial community, the relative abundance of Bacillus and Lysinibacillus were increased compared to the CG. Additionally, the serum metabolome results revealed a negative correlation between Lysinibacillus abundance and lipid metabolites in the serum. These findings suggested that supplementing the diet with 3.75 g/kg CT promoted the growth performance, feed utilization, and intestinal health of largemouth bass. The optimum CT level was 4.15 g/kg based on second-order polynomial regression analyses of weight gain rate.

Unlocking the potential: Cinnamomum cassia (L.) D. Don aqueous extracts as natural defenders against MSRV in largemouth bass aquaculture

Aquatic viral diseases pose significant threats to aquaculture, necessitating the exploration of effective preventive measures. In this study, we evaluated the antiviral potential of Cinnamomum cassia (L.) D. Don (CCD) aqueous extracts against Micropterus salmoides rhabdovirus (MSRV) in largemouth bass aquaculture. Initially, twelve plant extracts were screened for antiviral activity against MSRV, revealing that CCD extracts at 100 mg/L concentration significantly inhibited MSRV proliferation in vitro. Further dose-response analysis revealed a concentration-dependent antiviral effect of CCD extracts, with higher concentrations demonstrating increased efficacy against MSRV. Subsequent investigations focused on the protective effects of CCD extracts on MSRV-infected cells. At a concentration of 63 mg/L, CCD extracts significantly reduced MSRV titers, preventing the onset of cytopathic effects (CPE) in cells. Fluorescence and transmission electron microscopy further illustrated the protective effects of CCD extracts on cellular morphology. MSRV-infected cells treated with CCD exhibited preserved cell morphology akin to normal cells, contrasting with the typical apoptotic features observed in untreated infected cells. Additionally, dietary supplementation of CCD extracts in largemouth bass demonstrated notable benefits. Fish fed with CCD extracts exhibited increased survival rates when infected with MSRV, with a 26 % higher survival rate compared to the virus-only group. Furthermore, CCD supplementation enhanced the expression of interferon-gamma (IFNγ), indicating improved immune responses in largemouth bass. Moreover, immersion of CCD extracts in water showed partial inhibition of horizontal MSRV transmission, effectively reducing viral spread and mitigating disease risks in fish populations. These findings highlight the potential of CCD aqueous extracts as feed additives for combating MSRV in aquaculture, showcasing their promising application prospects in disease prevention and control strategies.

γ-aminobutyric acid improves the growth performance, food intake and glucose homeostasis of Micropterus salmoides fed high-carbohydrate diets

This study aimed to assess the function of γ-aminobutyric acid (GABA) on growth performance, food intake and glucose homeostasis of Micropterus salmoides fed carbohydrate (CHO)-enriched diets. The intracerebroventricular glucose + GABA co-injected fish had higher cumulative food intake, and expression of orexigenic genes (ghrelin and neuropeptide y (npy)) in the brain than those of the single glucose-injected group. In the feeding trial, M. salmoides (10.35 ± 0.05 g) were fed four feeds containing a control feed (10 % CHO, C) and three GABA contents [0 (HC), 50 (HC-G1), and 100 (HC-G2) mg kg−1, respectively] of high-CHO feed (20 % CHO) for 12 weeks. High CHO prominently (P < 0.05) decreased WGR, SGR, FI, p-Ampk protein content, and expression of ghrelin, npy, fbpase, pparα, cpt1α and aco1 compared with the control group, but the opposite was true for plasma glucose and triglyceride levels, tissue glycogen and lipid contents, and expression of proopiomelanocortin, leptin a, gk, pk, gs, chrebp, srebp1, fas and acc1. HC-G2 diets prominently (P < 0.05) up-regulated WGR, SGR, FI, p-Ampk protein content, and expression of ghrelin, npy, gk, pk, chrebp, srebp1, fas and acc1 compared with the HC group. Also, HC-G2 diets increased glucose tolerance of M. salmoides fed high-CHO diets after glucose loading. Overall, GABA improved the growth performance, food intake and glucose homeostasis of high-CHO-fed fish by the increase of appetite, glycolysis, glycogenesis and lipolysis, as well as the inhibition of gluconeogenesis and lipid synthesis.

Evaluating the efficacy of ecological restoration of fish habitat in coastal waters of Lake Ontario

Ecological restoration is a common strategy applied to degraded wetlands and tributaries in large lakes. As resources are typically limited for restoration, it is essential to ensure that such efforts achieve associated goals. Using both discrete and continuous methods, we evaluated the efficacy of ecological restoration efforts on fish habitat within Canada's largest city, Toronto (Cell 2 and Embayment D of Tommy Thompson Park) relative to a control site (Toronto Islands). First, we used a long-term electrofishing dataset (i.e., discrete) to examine catch and community composition relative to restoration status. Catch for northern pike (Esox lucius) remained constant at both restoration sites, and catch of invasive common carp (Cyprinus carpio) decreased at Embayment D, indicating that exclusion barriers may be effective. Restoration was less effective for largemouth bass (Micropterus nigricans) as catches remained similar after restoration at Cell 2, but decreased within Embayment D. We also found that relative abundance for coldwater species at both restoration sites decreased post-restoration, with increases in warmwater species at Cell 2 and coolwater species at Embayment D. Next, we used a long-term acoustic telemetry dataset (i.e., continuous sampling) with three focal species: largemouth bass, northern pike, and invasive common carp. Based on telemetry, we found that restoration efficacy was species-specific, with largemouth bass present before and after ecological restoration (particularly in spring, which may be associated with spawning), but clear reductions in use of the restored areas for common carp and northern pike. Exclusion barriers, while effective at blocking common carp, appeared to also negatively influence access for northern pike. Using both discrete and continuous methods longitudinally and across both treatment and control sites provided complementary information on the efficacy of restoration works within Toronto Harbour, with electrofishing data highlighting changes in fish community composition while acoustic telemetry provided continuous information on timing and duration of habitat use.

Spatial and Ontogenetic Patterns in the Trophic Ecology of Two Predatory Fishes in a Large River

ABSTRACTFishes use a variety of physical and biological resources that shift ontogenetically, seasonally and spatially. Quantifying what resources such as prey are required for persistence can improve understanding of ecological needs of fishes and riverine macrosystem functioning. Bowfin (Amia ocellicauda) and largemouth bass (Micropterus nigricans) cohabitate in their native range and potentially compete with one another. Yet, there have been no direct comparisons of their diets across spatial gradients to assess whether they partition resources or shift in prey use. We used multiple univariate and multivariate analyses to compare diet composition, diet overlap, feeding strategy, prey importance and diet partitioning between largemouth bass and bowfin across three reaches of the Upper Mississippi River. Largemouth bass ontogenetically shifted their diet from aquatic invertebrates to fishes and a more diverse assemblage of aquatic invertebrates. Bowfin and adult largemouth bass were top predators which consumed mostly crayfish and fish and overlapped in their diets. Despite overlapping diets, predators partitioned resources by consuming different lengths and abundances of prey, and largemouth bass had greater trophic plasticity. Within a predator group, few differences in diets existed spatially, underscoring the relative homogeneity in resource use potentially from similarities in the river's physical structure. Combined, prey use likely differed sufficiently to reduce potential competition between largemouth bass and bowfin, allowing long‐term coexistence in this system. Our results also highlighted the importance of crayfishes to riverine food webs and underscored the use of multiple prey and habitat types that sustain these predators.

Physiological and immune responses of largemouth bass (Micropterus salmoides) under the regulation of exercise intensity: An integrated perspective of blood, liver and intestinal analysis

This study examined the effects of different water flow durations on serum biochemical indices, liver antioxidant capacity, and intestinal health of largemouth bass (Micropterus salmoides) in a recirculating aquaculture system (RAS). During a 90-day experiment, 270 largemouth bass (initial weight 96.05 ± 18.87 g) were randomly assigned to three groups: a control group (CG) with a constant flow velocity of 0.3 cm/s, an interval exercise group (IE) with a water flow velocity of 2 bl/s for 8 h/day, and a sustained exercise group (SE) with a continuous flow velocity of 2 bl/s for 24 h/day. The results showed that the IE group had higher total protein (TP) levels than the CG and SE groups (P < 0.05). In contrast, the SE group had lower triglyceride (TG) and cholesterol (CHO) levels (P < 0.05), indicating that exercise intensity significantly affects serum biochemical parameters. The study also evaluated the effects of sustained swimming on liver antioxidant capacity, digestive enzyme activity, intestinal health, and microbial community composition. Antioxidant assays revealed significantly increased activities of superoxide dismutase (T-SOD) and catalase (CAT) in the SE group, along with the lowest malondialdehyde (MDA) levels (P < 0.05), indicating enhanced antioxidant defenses. Enzyme assays showed a significant increase in trypsin and lipase activities due to swimming exercise (P < 0.05). Intestinal morphology analysis showed increased villus height and wall thickness in the SE group, without visible tissue damage, suggesting improved intestinal structural integrity. Gene expression analysis showed a significant upregulation of pro-inflammatory genes in the IE group and an increase in anti-inflammatory gene expression in the SE group. Microbial community analysis showed no significant differences in alpha diversity, species richness, or total diversity among the groups. However, variations in microbial species distribution at the phylum and genus level were observed, which were likely influenced by exercise intensity. In conclusion, sustained swimming exercise significantly improved antioxidant capacity, intestinal health, and modulated the immune response in largemouth bass. This highlights its potential to improve fish health and sustainability in RAS.

Effects of dietary tocotrienol on growth, digestive enzyme activities, antioxidant capacity, histology, and disease resistance of Largemouth Bass fingerlings

AbstractObjectiveWe sought to assess the efficacy of feeding tocotrienol, a member of the vitamin E family, as it impacts physiological functions in fingerling fish.MethodsFingerling Largemouth Bass Micropterus nigricans with an initial mean body weight (±SD) of 0.98 ± 0.09 g were fed five diets containing tocotrienol at 0, 10, 20, 30, and 40 mg/kg (T0, T10, T20, T30, and T40 diets, respectively) for 42 days. After the feeding experiment, fish were challenged with Largemouth Bass ranavirus (LMBV) and monitored for 48 h.ResultFindings indicated a positive impact of tocotrienol‐supplemented diets on fingerling survival. Furthermore, the weight gain and specific growth rate of fish that received the T30 and T40 diets were significantly higher than those of fish that were fed the T0 diet. Tocotrienol supplementation improved the protein efficiency ratio and condition factor and increased the whole‐body lipid and protein content. Conversely, the hepatosomatic index, viscerosomatic index, and feed conversion ratio were significantly decreased by tocotrienol supplementation. Fish that were fed the T30 and T40 diets exhibited significantly higher hepatopancreas lipase activity and intestinal protease activity. Generally, superoxide dismutase and catalase activities in the liver increased as the tocotrienol level increased. Additionally, the liver malondialdehyde concentration decreased, and there was an improvement in the structure of liver cell tissue. Survival at 48 h after the LMBV challenge was significantly higher in fish that were fed the T30 and T40 diets compared to fish that were given the T0 diet. Maximum specific growth rate was observed at a tocotrienol concentration of 33.63 mg/kg.ConclusionResults suggest that supplementation of Largemouth Bass fingerling diets with appropriate quantities of tocotrienol can enhance survival, growth, antioxidant capacity, digestion, and uptake of nutrients as well as disease resistance.

Delayed Reproduction, Injury, and Regeneration of Testes in Out-of-Season Breeding of Largemouth Bass (Micropterus nigricans).

Out-of-season breeding is an effective method for addressing seasonal shortages of fry in aquaculture species such as largemouth bass (LMB) for year-round production. Off-season breeding of LMB can be achieved by subjecting breeding LMB to prolonged low-temperature conditions; however, this can alter reproductive rhythms, affecting the quality of their sperm and leading to a decrease in reproductive efficiency. Therefore, it is crucial to investigate issues such as the damage to the testes and the related mechanisms caused by low-temperature stress during out-of-season breeding. In this experiment, we assessed the changes in the testes during this time in LMB by comparing reproductive rhythms, testicular histomorphology, ultrastructure, antioxidant capacity and apoptosis. We synthesized measurements of LMB from three identically treated cement ponds and fish exposed to water temperatures of 13-16 °C to assess the changes in the testes. The results showed that (1) out-of-season reproduction delayed sperm production and promoted sperm redevelopment in LMB, various hormone levels have changed over time (e.g., LH, FSH, and T). (2) The head plasma membrane of LMB spermatozoa was separated, and the middle mitochondria were swollen. (3) The expression levels of antioxidant enzymes (cat, sod, and gpx) were upregulated, and oxidative stress occurred in LMB. (4) The expression levels of apoptosis genes (e.g., bax, bcl2, and caspase3) were upregulated, and apoptosis occurred in LMB due to off-season breeding. Moreover, important genes of the mitochondrial apoptosis pathway (bid, CYT-C) were upregulated, indicating that spermatozoan apoptosis in LMB was probably achieved through the mitochondrial apoptosis pathway. These results suggest the delays, damage, and regeneration of LMB testes. Our findings provide new insights into the molecular mechanisms that trigger changes in sperm quality during out-of-season breeding in fish.

Oral administration of recombinant Lactococcus lactis expressing largemouth bass (Micropterus salmoides) IFNa3 protein enhances immune response against largemouth bass virus (LMBV) infection

Largemouth bass virus (LMBV) is a highly pathogenic pathogen that often causes high mortality of affected largemouth bass and significant financial losses. Type I interferon as an effective and broad spectrum tool has been successfully used for therapeutic or prophylactic treatment some viral infections. However, the implementation of immunotherapies based on interferon administration to combat LMBV infections has not been reported. And Lactic Acid Bacteria (LAB) are a powerful vehicle for expressing cytokines or immunostimulant peptides at the gastrointestinal level after oral administration. In this study, Lactococcus lactis (L. lactis) expression system with lactose as a screening marker was utilized to express the Micropterus salmoides interferon a3 (IFNa3) protein and orally administered to largemouth bass. The genetically engineered strain pNZ8149-Usp45-IFNa3-6His/L. lactis NZ3900 was successfully constructed, and its potential to elicit immune protection response by oral administration was evaluated. After orally administration, the recombinant L. lactis was detected in guts of experimental fish and remained detectable for 72 h. Additionally, IFNa3 was able to enhance the test fish's immune response, as determined by the relatively increased mRNA relative expression of immune-related genes in the liver, spleen, and kidney tissues, including IFN-γ, TNF-α, IL-1β, IL-8, IgM and IgT. Following LMBV challenge, the experiment group of pNZ8149-Usp45-IFNa3-6His/L. lactis NZ3900 exhibited a 70 % survival rate, while survival rate were 15 % in the PBS control group, 45 % in the pNZ8149/L. lactis NZ3900 group. Furthermore, the viral load in the surviving fish was significantly lower than that of the control groups. These findings suggest that oral administration of recombinant L. lactis producing IFNa3 induces largemouth bass immune responses at a systemic level to effective prevent and combat of LMBV infection.