Largemouth Research Articles

Effects of exercise training on growth and physiology of large-mouth bass (Micropterus salmoides) reared in a recirculating aquaculture system

Large-mouth bass originally lived in rivers and lakes and now is often raised in recirculating aquaculture systems (RAS). However, the shortcoming of RAS is that there is very limited space for swimming fish in a high-density culture environment, thus leading to a lack of exercise. To investigate the effects of exercise training on growth performance, digestive enzymes, stress, and antioxidant capacity of large-mouth bass in a RAS, three training water flow velocities with three replicates were used in the present study: low water velocity: 0.5 body length per second (bl/s) (LV); medium water velocity: 1 bl/s (MV); and high water velocity: 1.5 bl/s (HV). 270 large-mouth bass (average initial body weight 47.51 ± 1.44 g, initial body length 12.71 ± 0.06 cm) were randomly divided into nine tanks (30 fish per tank). After 27 days experiment, the results showed that the growth performance of large-mouth bass, including feed intake, weight gain rate, and specific growth rate, in the HV group was significantly higher compared to the other groups. On the physiological level, the lipase and amylase activities were significantly increased in the HV group compared to the other groups. For the stress response parameters, the cortisol, glucose and lactate concentrations in the HV group were significantly increased, which may indicate higher stress in the HV group. Regarding the antioxidant enzyme activities, the activities of catalase (CAT) and glutathione peroxidase (GSH-PX) in the LV group were significantly higher than those in the HV group, which indicated that fish suffered higher oxidative stress in the LV group. Regarding the immune-related parameters, LZM and ACP activities had no significant differences among the groups, while AKP activities in the MV and HV groups were significantly higher than that in the LV group. Overall, the results demonstrated that exercise training had significant effects on the growth, digestion, stress, and immune response of large-mouth bass. It is suggested that exercise training with 1.5 bl/s can enhance fish growth, however, it also presents a potential risk of inducing stress in fish. Therefore, in rearing large-mouth bass in RAS, the setting of water flow velocity should not only focus on the growth of large-mouth bass but also consider its welfare.

Oral recombinant Pichia pastoris P-I20H combined with immunopotentiator curcumin remarkably inhibits and clears LMBV in largemouth bass (Micropterus salmoides)

Largemouth bass ranavirus (LMBV) causes massive losses in the largemouth bass industry. A promising therapeutic approach involves the oral administration of novel antimicrobial peptides (AMPs) and immunopotentiators. In this study, the Pichia pastoris expression system was employed for intracellular expression of AMP I20H. After meticulous screening, we successfully developed a strain, P-I20H-G7, demonstrating a high level of expression. Subsequently, we further optimized the induction conditions for this strain, including temperature, pH, and methanol concentration. Through these screening and optimization processes, we achieved an impressive nearly threefold increase in the production of I20H. Transmission electron microscopy, scanning electron microscopy and colony counting assays were utilized to confirm that P. pastoris effectively shielded I20H from the complex gastric and intestinal environments. Afterwards, P-I20H-G7 was lyophilized and co-fed with curcumin to largemouth bass infected by LMBV, the results indicated that oral administration of P-I20H-G7 combined with immunopotentiator curcumin effectively improve the survival rate of largemouth bass, with a 38% increase compared to the control group. qPCR demonstrated that dietary P-I20H-G7 + curcumin significantly inhibited and cleared LMBV within tissues. Additionally, oral administration of P-I20H-G7 + curcumin significantly upregulated the expression of key immune genes (IL-1β, IFN-γ, Mx, and IgM) and enhanced serum enzyme activities (TSOD, TAOC, and C3). Histopathological analysis revealed that P-I20H-G7 + curcumin treatment effectively mitigated tissue damage caused by LMBV infection. In conclusion, we successfully expressed and orally delivered I20H by the P. pastoris system and combined it with curcumin for efficiently curing diseased largemouth bass. These results underscore the potential of P-I20H-G7 + curcumin as a promising antiviral biological agent.

Analysis of relationship between growth traits and feed conversion ratio provides insights into aquaculture and breeding of largemouth bass Micropterus salmoides

Feed costs constitute the largest expense in aquaculture production. Therefore, studies on feed efficiency (FE), measured by feed conversion ratio (FCR), have attracted much attention from both breeders and researchers. In this study, the differences of growth traits and feed utilization traits between largemouth bass (LMB) with Low-FCR and High-FCR were compared, and the relationships and correlations between different traits were analyzed. The results showed that the Low-FCR group exhibited better growth performance expressed as higher weight gain (WG) and specific growth rate (SGR), and higher FE namely lower FCR and higher protein efficiency ratio (PER), than the High-FCR group. Thirteen of fourteen measured growth traits in the Low-FCR group were significantly higher than those in the High-FCR group. Seven normalized growth traits presented significant differences between the two groups, with the Low-FCR group observed to have a relatively larger body size. Additionally, in all individuals, the feeding rate (FR) showed significant correlations with the weight growth traits (WG and SGR) but not with the feed utilization traits (FCR and PER), suggesting the increase of FR can promote growth but have little effect on FE. Further, six equations were established to quantitatively estimate the effects of various morphological growth traits on growth and feed utilization. Finally, two discriminant equations were successfully constructed to distinguish Low-FCR and High-FCR LMB based on growth indexes. These results will enhance our understanding of the relationships between FE and growth traits and provide valuable reference information for selective breeding in FE for LMB.

Ecosystem responses to a whole‐reservoir coarse woody habitat addition

AbstractThe addition of coarse woody habitat (CWH) is often used to mitigate the loss of natural structure in aging waterbodies. Ecosystem‐scale effects of large‐scale CWH additions and their influence on fish productivity have been assessed in oligotrophic, natural lakes, but need to be assessed in more ecosystems. Therefore, we tested the effects of an ecosystem‐scale addition of CWH to a eutrophic reservoir using a reference reservoir and data from 4 years before and 4 years after habitat enhancement. Zooplankton and benthic macroinvertebrates did not respond to the addition of CWH, but bluegill (Lepomis macrochirus) reproductive productivity and largemouth bass (Micropterus salmoides) size structure increased. Positive fish responses that contrasted with a lack of fish population‐level responses after a similar CWH addition in an oligotrophic, natural lake highlight the importance of assessing the efficacy of CWH addition across diverse ecosystems.

C-Jun N-terminal kinase 1/P53 signaling mediates intrinsic apoptosis of largemouth bass (Micropterus salmoides) hepatocytes under heat stress

The increasing frequency of high-temperature extremes threatens largemouth bass Micropterus salmoides, a significant fish for freshwater ecosystems and aquaculture. Our previous studies at the transcript level suggested that heat stress induces hepatic apoptosis in largemouth bass. In the current study, we sought to validate these findings and further investigate the role of the c-Jun N-terminal kinase (JNK)/P53 signaling in hepatic apoptosis under heat stress. First, heat treatments were conducted in vivo and in vitro under different temperatures: 28 °C, 32 °C, and 37 °C. In primary hepatocytes subjected to heat treatment, cell viability was evaluated via the Cell Counting Kit-8, while mitochondrial membrane potential and nuclear morphology were assessed through JC-1 and Hoechst 33258 staining, respectively. We observed reductions in both cell viability and mitochondrial membrane potential (ΔΨm), along with alterations in nuclear morphology, in primary hepatocytes exposed to heat stress at temperatures of 32 °C and 37 °C. Quantitative real-time PCR revealed significant alterations in the expression profiles of intrinsic apoptosis-related genes within liver tissues under heat stress. Immunohistochemistry analysis revealed that JNK1 signaling increased as the temperature increased, JNK2 expression increased only at 37 °C, and JNK3 expression did not change with temperature. We speculate that JNK1 and JNK2 have pro- and anti-apoptotic effects, respectively. Western blot analysis conducted on cultured hepatocytes further validated these findings. JNK inhibition reduced hepatocyte apoptosis, improved nuclear morphology, and maintained ΔΨm even after 37 °C treatment. These results not only confirm that heat stress led to intrinsic apoptosis of hepatocytes but also indicated that JNK1 could mediate P53 expression and activate caspase-dependent intrinsic apoptosis in largemouth bass hepatocytes under such conditions. This study illuminates the physiological responses of largemouth bass to acute heat stress, offering valuable insights into the potential impacts of climate change on freshwater fishes and the sustainability of aquaculture.

Excessive Replacement of Fish Meal by Soy Protein Concentrate Resulted in Inhibition of Growth, Nutrient Metabolism, Antioxidant Capacity, Immune Capacity, and Intestinal Development in Juvenile Largemouth Bass (Micropterus salmoides).

This study investigated the effects of replacing 0% (SPC0), 25% (SPC25), 50% (SPC50), 75% (SPC75), and 100% (SPC100) of fish meal (FM) with soy protein concentrate (SPC) on the growth, nutritional metabolism, antioxidant capacity, and inflammatory factors in juvenile largemouth bass (Micropterus salmoides) (17.03 ± 0.01 g). After 56 days of culturing, various growth parameters including FW, WGR, and SGR were not significantly different among SPC0, SPC25, and SPC50 groups; however, they were significantly higher than those in SPC75 and SPC100 groups. Conversely, significantly lower FCR were determined for the SPC0, SPC25, and SPC50 groups compared with that for the SPC100 group; specifically, no significant difference among SPC0, SPC25, and SPC50 groups was found. Moreover, compared with SPC75 and SPC100 groups, a significantly higher FI was observed in the SPC0 group, whereas a significantly lower SR was observed in SPC100 compared with that in SPC0 and SPC25 groups. Compared with the SPC0 group, significantly lower mRNA levels of tor, rps6, 4ebp1, pparγ, and fas were found in SPC75 and SPC100. Additionally, the mRNA levels of cpt were significantly higher in SPC0, SPC25, and SPC50 groups than in SPC75 and SPC100 groups. Moreover, the mRNA levels of scd and acc remained unchanged for all the groups. Replacement of FM with SPC did not significantly affect the mRNA levels of gk, pk, and pepck. Compared with the SPC0 group, significantly decreased activities of CAT were observed in the SPC50, SPC75, and SPC100 groups, and significantly decreased activities of GSH-Px were observed in the SPC75 and SPC100 groups. In addition, significantly lower activity of SOD was observed in SPC100 compared with the other groups. Moreover, compared with the other groups, the SPC75 and SPC100 groups had significantly decreased and increased contents of GSH and MDA, respectively, while significantly lower mRNA levels of nrf2, cat, sod, and gsh-px were found in SPC50, SPC75, and SPC100; however, significantly higher mRNA levels of keap1 were observed in SPC75 and SPC100 groups. Additionally, significantly higher mRNA levels of il-8 and nf-κb were found in the SPC50, SPC75, and SPC100 groups compared with the SPC0 group. Conversely, significantly lower mRNA levels of il-10 and significantly higher mRNA levels of tnf-α were found in the SPC75 and SPC100 groups compared with the other groups. Compared with the SPC0 group, mucosal thickness and villus height were significantly decreased in the SPC75 and SPC100 groups. Collectively, SPC replacing 50% FM did not affect its growth of juvenile largemouth bass. However, SPC replacing 50% or more FM might inhibit antioxidant capacity and immune capacity to even threaten the SR, resulting in impaired intestinal development in replacing FM level of 75% or more.

Effects of dietary salidroside on intestinal health, immune parameters and intestinal microbiota in largemouth bass (Micropterus salmoides)

The largemouth bass has become one of the economically fish in China, according to the latest China Fishery Statistical Yearbook. The farming scale is constantly increasing. Salidroside has been found in past studies to have oxidative stress reducing and immune boosting properties. In this study, the addition of six different levels of salidroside supplements were 0、40、80、120、160 and 200 mg/kg. A 56-day feeding trial was conducted to investigate the effects of salidroside on the intestinal health, immune parameters and intestinal microbiota composition of largemouth bass. Dietary addition of salidroside significantly affected the Keap-1β/Nrf-2 pathway as well as significantly increased antioxidant enzyme activities resulting in a significant increase in antioxidant capacity of largemouth bass. Dietary SLR significantly reduced feed coefficients. The genes related to tight junction proteins (Occludin, ZO-1, Claudin-4, Claudin-5) were found to be significantly upregulated in the diet supplemented with salidroside, indicating that salidroside can improve the intestinal barrier function (p < 0.05). The dietary administration of salidroside was found to significantly reduce the transcription levels of intestinal tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) (p < 0.05). Furthermore, salidroside was observed to reduce the transcription levels of intestinal apoptosis factor Bcl-2 associated death promoter (BAD) and recombinant Tumor Protein p53 (P53) (p < 0.05). Concomitantly, the beneficial bacteria, Fusobacteriota and Cetobacterium, was significantly increased in the SLR12 group, while that of pathogenic bacteria, Proteobacteria, was significantly decreased (p < 0.05). In conclusion, the medium-sized largemouth bass optimal dosage of salidroside in the diet is 120mg/kg−1.

Hepatic Oxidative Stress and Cell Death Influenced by Dietary Lipid Levels in a Fresh Teleost.

Ferroptosis is a form of regulated cell death characterized by iron-dependent lipid peroxidation, affecting physiological and pathological processes. Fatty liver disease associated with metabolic dysfunction is a common pathological condition in aquaculture. However, the exact role and mechanism of ferroptosis in its pathogenesis and progression remains unclear. In this study, an experiment was conducted using different dietary lipid levels in the feeding of largemouth bass (Micropterus salmoides) for 11 weeks. The results revealed that the growth performance and whole-body protein content significantly increased with the elevation of dietary lipid levels up to 12%. The activities of antioxidant enzymes as well as the content of GSH (glutathione) in the liver initially increased but later declined as the lipid levels increased; the contents of MDA (malondialdehyde) and GSSG (oxidized glutathione) demonstrated an opposite trend. Moreover, elevating lipid levels in the diet significantly increased liver Fe2+ content, as well as the expressions of TF (Transferrin), TFR (Transferrin receptor), ACSL4 (acyl-CoA synthetase long-chain family member 4), LPCAT3 (lysophosphatidylcholine acyltransferase 3), and LOX12 (Lipoxygenase-12), while decreasing the expressions of GPX4 (glutathione peroxidase 4) and SLC7A11 (Solute carrier family 7 member 11). In conclusion, the optimal lipid level is 12.2%, determined by WG-based linear regression. Excess lipid-level diets can up-regulate the ACSL4/LPCAT3/LOX12 axis, induce hepatic oxidative stress and cell death through a ferroptotic-like program, and decrease growth performance.

Effects of High Dietary Starch Levels on the Growth Performance, Liver Function, and Metabolome of Largemouth Bass (Micropterus salmoides)

In this study, we conducted a 16-week feeding trial to investigate the effects of a high-cassava starch diet on growth performance, liver function, and metabolism in largemouth bass (Micropterus salmoides). We formulated five diets containing varying levels of cassava starch: 12%, 9%, 6%, 3%, and 0% (termed M12, M9, M6, M3, and M0, respectively). We distributed these diets among largemouth bass with the initial body weight of 83.33 ± 0.55 g via an in-pond “raceway” aquaculture system. Our findings suggest that high level (12%) of cassava starch dietary inclusion adversely affected growth performance metrics such as weight gain rate and specific growth rate, along with feed utilization efficiency indicators, including protein efficiency, protein deposition rate, and the apparent digestibility of dry matter and protein. This negative impact was accompanied by a decrease in intestinal amylase activity. Through further transcriptomic analysis, we identified several key genes associated with carbohydrate metabolism, which underwent changes influencing liver function. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed the involvement of these differentially expressed genes (DEGs) in the tricarboxylic acid cycle (TCA cycle). Comparative metabolomics analysis further indicated that the M9 group showed significant enrichment in pathways related to amino acid metabolism and alterations in the levels of metabolites involved in carbohydrate metabolism. In conclusion, our study demonstrates that incorporating up to 9% cassava starch in the diet can enhance growth performance in largemouth bass by stimulating digestive enzyme activities and promoting glucose utilization.

Hydrolysable tannin improves growth performance and liver health of largemouth bass (Micropterus salmoides) fed high soybean meal diets

This study provided evidence that the inclusion of hydrolysable tannin (HT) in high soybean meal (SBM) diets improved growth performance and glycolipid metabolism of largemouth bass (Micropterus salmoides). In vivo, various levels of HT were added to high SBM diets and fed to largemouth bass (initial weight: 6.00 ± 0.03 g) for 56 days. Results showed that a high level of SBM led to the reduction in growth performance, as evidenced by decreased weight gain rate and impaired hepatic function. Dietary supplementation with HT (1.0 g/kg) improved growth performance of largemouth bass, accompanied by the enhancements in hepatic antioxidant capacity and glycolipid metabolism. In vitro, HT facilitated glucose utilization in hepatocytes and positively influenced the modulation of crucial genes within the PI3K/Akt signaling pathway. Conversely, administration of LY294002 (a PI3K inhibitor) reversed the detrimental effects observed in hepatocytes exposed to high glucose levels. Overall, incorporating HT (1.0 g/kg) into the diet enhanced liver health and improved the absorption and utilization of SBM in largemouth bass, potentially achieved through modulation of the PI3K/Akt signaling pathway.

Longitudinal distribution of fish fauna and characteristics of indicator species in the East Seto Inland Ecological Region within the Japanese Archipelago

Understanding biota distribution patterns is essential for ecosystem conservation and restoration. In addition to biogeography, the distribution patterns of aquatic organisms that inhabit rivers vary longitudinally along river networks. Although longitudinal changes in distribution patterns in aquatic organisms along river networks have been studied in single river basins, it is crucial to understand these patterns at a regional ecological scale for broad-scale ecosystem conservation. This study aimed to elucidate the longitudinal distribution patterns of fish fauna and their correlation with environmental factors in several watersheds within the East Setouchi Ecological Region, renowned for its rich freshwater fish diversity in the Japanese archipelago. Data were obtained for 118 species across 10 watersheds and 85 sites, and the surveyed sites were classified into four longitudinal groups based on the similarity of the fish fauna. The lowest group comprised river estuaries, abundant in brackish-water fish, comprising primarily Gobiidae species. In lower watershed areas with low agricultural land and forest cover but high urbanization, all fish species selected as indicators were non-native. Upstream areas with a high percentage of agricultural land featured a mix of native Cyprinidae and non-native species such as Micropterus salmoides and Rhodeus ocellatus ocellatus. The most upstream groups, marked by significantly greater elevations and bed slopes, exclusively comprised native species as indicator species. Analyzing the longitudinal distribution patterns of fish fauna at multiple sites within the same ecological region enabled us to choose endemic fish species as indicators and identify important species for conservation. Additionally, the selection of sites characterized by significant urbanization and strong anthropogenic influences, along with the selection of non-native species as indicators, underscores the urgency of conserving native organisms in these areas, calling for continuous monitoring.

Using heart rate and acceleration biologgers to estimate winter activity costs in free-swimming largemouth bass

Winter is a critical period for largemouth bass (Micropterus nigricans) with winter severity and duration limiting their population growth at northern latitudes. Unfortunately, we have an incomplete understanding of their winter behaviour and energy use in the wild. More winter-focused research is needed to better understand their annual energy budget, improve bioenergetics models, and establish baselines to assess the impacts of climate warming; however, winter research is challenging due to ice cover. Implantable tags show promise for winter-focused research as they can be deployed prior to ice formation. Here, using swim tunnel respirometry, we calibrated heart rate and acceleration biologgers to enable estimations of metabolic rate (ṀO2) and swimming speed in free-swimming largemouth bass across a range of winter-relevant temperatures. In addition, we assessed their aerobic and swim performance. Calculated group thermal sensitivities of most performance metrics indicated the passive physicochemical effects of temperature, suggesting little compensation in the cold; however, resting metabolic rate and critical swimming speed showed partial compensation. We found strong relationships between acceleration and swimming speed, as well as between ṀO2 and heart rate, acceleration, or swimming speed. Jackknife validations indicated that these modeled relationships accurately estimate swimming speed and ṀO2 from biologger recordings. However, there were relatively few reliable heart rate recordings to model the ṀO2 relationship. Recordings of heart rate were high-quality during holding but dropped during experimentation, potentially due to interference from aerobic muscles during swimming. The models informed by acceleration or swimming speed appear to be best suited for field applications.

Growth, Antioxidant Capacity, and Liver Health in Largemouth Bass (Micropterus salmoides) Fed Multi-Strain Yeast-Based Paraprobiotic: A Lab-to-Pilot Scale Evaluation.

A multi-strain yeast-based paraprobiotic (MsYbP) comprising inactive cells and polysaccharides (β-glucan, mannan oligosaccharides, and oligosaccharides) derived from Saccharomyces cerevisiae and Cyberlindnera jadinii could ensure optimal growth and health in farmed fish. This study assessed the impact of an MsYbP on the growth, immune responses, antioxidant capacities, and liver health of largemouth bass (Micropterus salmoides) through lab-scale (65 days) and pilot-scale (15 weeks) experiments. Two groups of fish were monitored: one fed a control diet without the MsYbP and another fed 0.08% and 0.1% MsYbP in the lab-scale and pilot-scale studies, respectively (referred to as YANG). In the lab-scale study, four replicates were conducted, with 20 fish per replicate (average initial body weight = 31.0 ± 0.8 g), while the pilot-scale study involved three replicates with approximately 1500 fish per replicate (average initial body weight = 80.0 ± 2.2 g). The results indicate that the MsYbP-fed fish exhibited a significant increase in growth in both studies (p < 0.05). Additionally, the dietary MsYbP led to a noteworthy reduction in the liver function parameters (p < 0.05), such as alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (AKP), and hepatic nuclear density, indicating improved liver health. Furthermore, the dietary MsYbP elevated the antioxidative capacity of the fish by reducing their malondialdehyde levels and increasing their levels and gene expressions related to antioxidative markers, such as total antioxidant ca-pacity (T-AOC), total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), catalase (CAT), nuclear factor erythroid 2-related factor 2 (nrf2) and kelch-1ike ech-associated protein (keap1) in both studies (p < 0.05). In terms of hepatic immune responses, the lab-scale study showed an increase in inflammation-related gene expressions, such as interleukin-1β (il-1β) and transforming growth factor β1 (tgf-β1), while the pilot-scale study significantly suppressed the expressions of genes related to inflammatory responses, such as tumor necrosis factor α (tnfα) and interleukin-10 (il-10) (p < 0.05). In summary, our findings underscore the role of dietary multi-strain yeast-based paraprobiotics in enhancing the growth and liver health of largemouth bass, potentially through increased antioxidative capacity and the modulation of immune responses, emphasizing the significance of employing yeast-based paraprobiotics in commercial conditions.

Single-Cell Transcriptomic Analysis Revealed the Cell Population Changes and Cell–Cell Communication in the Liver of a Carnivorous Fish in Response to High-Carbohydrate Diet

BackgroundCarnivorous fish have a low carbohydrate utilization ability, and the physiologic and molecular basis of glucose intolerance has not been fully illustrated. ObjectivesThis study aimed to use largemouth bass as a model to investigate the possible mechanism of glucose intolerance in carnivorous fish with the help of single-nuclei RNA sequencing (snRNA-seq). MethodsTwo diets were formulated, a low-carbohydrate (LC) diet and a high-carbohydrate (HC) diet. The feeding trial lasted for 6 wk, and then, growth performance, biochemical parameters, liver histology, and snRNA-seq were performed. ResultsGrowth performance of fish was not affected by the HC diet, while liver glucolipid metabolism disorder and liver injury were observed. A total of 13,247 and 12,848 cells from the liver derived from 2 groups were isolated and sequenced, and 7 major liver cell types were annotated by the marker genes. Hepatocytes and cholangiocytes were lower and hepatic stellate cells (HSCs) and immune cells were higher in the HC group than those in the LC group. Reclustering analysis identified 7 subtypes of hepatocytes and immune cells, respectively. The HSCs showed more cell communication with other cell types, and periportal hepatocytes showed more cell communication with other hepatocyte subtypes. Cell–cell communication mainly focused on cell junction–related signaling pathways. Uncovered by the pseudotime analysis, midzonal hepatocytes were differentiated into 2 major branches—biliary epithelial hepatocytes and hepatobiliary hybrid progenitor. Cell junction and liver fibrosis–related genes were highly expressed in the HC group. HC diet induced the activation of HSCs and, therefore, led to the liver fibrosis of largemouth bass. ConclusionsHC diet induces liver glucolipid metabolism disorder and liver injury of largemouth bass. The increase and activation of HSCs might be the main reason for the liver injury. In adaption to HC diet, midzonal hepatocytes differentiates into 2 major branches—biliary epithelial hepatocytes and hepatobiliary hybrid progenitors.

Establishment of an LMBV-infection model in zebrafish larvae and its application in studying virus-host interactions

Largemouth bass virus (LMBV) causes high transmission efficiency and mortality in freshwater aquaculture industry. However, the host responses to LMBV infection, particularly the molecular mechanisms involved in vivo, remain largely uncertain. Zebrafish has been developed as a powerful model organism for the study of host inflammation and immune response upon pathogen infections. Here, we evaluated the susceptibility of LMBV to zebrafish larvae and investigated the host response upon virus infection using transcriptomic analysis. LMBV replicated well in larvae by inoculation with LMBV via the brain and the duct of Cuvier, but the later showed more severe systemic infection, evidenced by the cumulative mortality, the increased transcriptions of viral core genes, and the presence of mcp positive signal in infected larvae. After inoculation with LMBV via the duct of Cuvier, we observed numerous viral particles in the head and tail regions of infected larvae. Moreover, ROS and TUNEL positive signaling also significantly increased in LMBV infected larvae. Of note, a great deal of neutrophils migrated towards the virus infected sites during LMBV infection. Transcriptomic analysis showed that a total of 1263 genes were up-regulated and 1039 genes were down-regulated in response to LMBV infection. Enrichment analysis indicated that the majority of the enriched KEGG pathways were associated with metabolism, cell death and immune regulation, such as fatty acid metabolism, steroid hormone biosynthesis, PPAR signaling, apoptosis, necroptosis, phagosome, cytokine-cytokine receptor pathway, NOD-like receptor signaling, and toll-like receptor pathway. For instance, cell death related signaling molecules including casp9,fas,tnfα and sqstm1 were significantly up-regulated, while camk2a,sept4b and akt1 were down-regulated in response to LMBV infection. Thus, our data firstly established LMBV-infected model in zebrafish larvae which could provide an alternative means for investigation of LMBV-host interaction in vivo, and application for high throughput drug screening in the future.

Intermittent swimming and muscle power output in brook trout, Salvelinus fontinalis.

Slow and sustainable intermittent swimming has recently been described in several Centrarchid fishes, such as bluegill and largemouth bass. This swimming behavior involves short periods of body-caudal fin undulation alternating with variable periods of coasting. This aerobic muscle powered swimming appears to reduce energetic costs for slow, sustainable swimming, with fish employing a "fixed-gear" or constant tailbeat frequency and modulating swimming speed by altering the length of the coasting period. We asked if this swimming behavior was found in other fish species by examining volitional swimming by brook trout in a static swimming tank. Further, we employed muscle mechanics experiments to explore how intermittent swimming affects muscle power output in comparison to steady swimming behavior. Brook trout regularly employ an intermittent swimming form when allowed to swim volitionally, and consistently showed a tailbeat frequency of ~2 Hz. Coasting duration had a significant, inverse relationship to swimming speed. Across a range of slow, sustainable swimming speeds, tailbeat frequency increased modestly with speed. The duration of periods of coasting decreased significantly with increasing speed. Workloop experiments suggest that intermittent swimming reduces fatigue, allowing fish to maintain high power output for longer compared to continuous activity. This study expands the list of species that employ intermittent swimming, suggesting this behavior is a general feature of fishes.

Population life‐history differences and their correlates across a regional spatial scale in largemouth bass (Micropterus nigricans)

Population life‐history differences and their correlates across a regional spatial scale in largemouth bass (<i>Micropterus nigricans</i>)

Dietary threonine influences antioxidant capacity and immune status in juvenile largemouth bass (Micropterus salmoides)

As a restricted amino acid, threonine (Thr) deficiency reduces antioxidant and immune capacity in fish. In the present study, six diets containing different Thr levels (1.39 %, 1.71 %, 1.95 %, 2.28 %, 2.58 %, and 2.65 %) were fed to largemouth bass (15±0.1 g) for 60 days. The present results showed that neither growth nor whole-body composition was affected by different Thr levels. And low dietary Thr levels (1.39 %) significantly decreased serum total protein (TP) and albumin (ALB) levels, but increased alkaline phosphatase (ALP) levels. And 1.39 % Thr diet significantly decreased liver catalase (CAT) activity but increased malonaldehyde (MDA) levels, and the maximum total antioxidant capacity (T-AOC) was observed in response to the 1.95 % Thr diet. Liver proapoptotic factors (bax and caspase9) were significantly elevated in fish fed the 1.39 % Thr diet. The nuclear factor κB (nf-κb) and the NF-κB-mediated inflammatory cytokines were significantly increased in fish fed the 1.39 % Thr diet. The mRNA levels of protein kinase R (PKR)-like endoplasmic reticulum kinase (perk), eukaryotic translation initiation factor 2 (eif2α), activating transcription factor 4 (atf4), and C/EBP-homologous protein (chop), which are factors in the PERK/ATF4/CHOP pathway, one of the unfolded protein response (UPR) signaling pathways, were significantly increased by the 1.39 % Thr diet. The present study showed that low dietary Thr levels caused oxidative damage, reduced immunity, might affected PERK-ATF4-CHOP signaling to induce apoptosis, and via NF-κB signaling to trigger an inflammatory response in largemouth bass. Based on the TP, ALB, CAT, and MDA levels, the dietary Thr requirements for juvenile largemouth bass were estimated to be 2.18 %, 2.29 %, 1.92 %, and 1.88 %. Furthermore, these findings provided a new perspective that low dietary amino acid levels may trigger apoptosis and inflammatory responses in fish through the UPR signaling pathway.

Use of Fin Rays and Fin Spines in Nonlethal Age Estimation of Florida Bass

Abstract Nonlethal age-estimation methods for Florida Bass Micropterus salmoides using fin rays and spines would enhance trophy-bass research, management, and conservation. Nonlethal removal of fin structures would also expand opportunities for collecting age-related information, specifically during small-population projects as well as tournaments and citizen-science programs, for which sacrificing fish is not an option. We assessed the bias of age estimates derived from Florida Bass anal-, pelvic-, dorsal-, and pectoral-fin rays and anal-, pelvic-, and dorsal-fin spines by comparing them to age estimates derived from otoliths (i.e., sagittae), which are the standard for aging Florida Bass. We evaluated the precision of age estimates by calculating the absolute difference between replicate reads of each aging structure for each reader. Linear-mixed effects model selection indicated that precision was most affected by age, structure, and the age*structure interaction, in which the effect of age varied by structure. Age estimates from otoliths were the most precise, whereas pelvic spines were the least precise among all structures examined. Bias was similar across all fin structures, but the effect of age on bias varied by reader. Marginal increment analysis indicated that annulus formation was completed from November to March in Florida Bass dorsal spines, 5 mon earlier than in Florida Bass otoliths. Our results suggest that nonlethally removed fin structures, especially dorsal spines, have potential for use in estimating age, growth rates, mortality, and age structure of bass populations, which could be particularly beneficial where bass can reach unusual trophy sizes.

Predator presence influences survival and behavior of translocated stream fish in ponds

Abstract Small artificial impoundments such as farm ponds have recently been recognized as potential habitat for threatened native fish species. However, factors influencing translocation or colonization success into these environments, including connectivity to stream networks and interactions with existing fish community, are largely unknown. In this study we conducted a controlled experiment to quantify the influence of piscivorous Largemouth Bass Micropterus salmoides on the survival of a translocated native minnow species that we used as a surrogate for federally endangered Topeka Shiner Notropis topeka. We translocated or released 100 Bluntnose Minnow Pimephales notatus into each replicate treatment ponds with and without Largemouth Bass in the summers of 2020 and 2021. Each minnow was implanted with a passive integrated transponder (PIT) tag. Translocated populations were monitored using stationary and mobile passive integrated transponder antennas and estimates of apparent survival and probability of detection for each pond were derived from open population mark-recapture models. Apparent survival was nearly two times higher in ponds without bass suggesting predation by bass leads to higher mortality. Additionally, probability of detection was nearly 10 times higher in ponds without bass, suggesting reduced movement of translocated minnows when bass were present. While the direct effect of mortality impacts translocated populations, the indirect effect of altered behavior may also be impactful on translocation success. These results confirm that Largemouth Bass can limit the success of translocated minnow species.