Effects of Replacement of Dietary Fishmeal by Cottonseed Protein Concentrate on Growth Performance, Liver Health, and Intestinal Histology of Largemouth Bass (Micropterus salmoides)

Comparative Study on the Effects of Four Plant Protein Sources on the Liver and Intestinal Health of Largemouth Bass, Micropterus salmoides

The effects of plant protein sources (PPSs) on the health of the liver and intestine of the largemouth bass, Micropterus salmoides, were compared to verify the potential damaging effects of dietary fiber (DF). A diet containing 55% fish meal (FM) was used as the control. The test diets contained 25% soybean meal (SBM), rapeseed meal (RSM), cottonseed meal, or peanut meal, and the FM content was decreased to 30%. The protein and lipid contents of these five diets were balanced by casein and oil. Fish were raised for 8 weeks. The fish fed the diet containing PPS showed a trend of decreasing growth and apparent digestibility coefficients. The contents of total bile acid, lipid, and collagen in the liver were increased, and the mRNA expression levels of genes encoding inflammatory factors and enzymes involved in de novo fatty acid synthesis and bile acid synthesis were upregulated. Both the lipid and collagen contents in the liver were positively correlated with the DF content in the diet significantly. Morphology and histology showed reduced liver size, hepatic steatosis, and fibrosis in fish fed diets containing PPS. The lowest hepatosomatic index was observed in fish fed the SBM diet, and the most severe damage was observed in fish fed the RSM diet. No obvious histological abnormalities were observed in the hindgut. The bile acid profile in the liver could be used to distinguish the types of PPS very well by Fisher discriminant analysis. These results indicated that 25% of each of the four PPSs in the diet exceeded the tolerance range of largemouth bass and caused liver damage, which might be mediated by bile acid. DF in PPS might be an important agent contributing to liver damage.

Organic Ingredients as Alternative Protein Sources in the Diet of Juvenile Organic Seabass (Dicentrarchus labrax)

The use of organic ingredients as a source of protein in aquaculture diets has gained significant attention due to the growing demand for organic seafood products. This study aimed to evaluate the potential for the use of organic ingredients as protein sources in the diet of juvenile organic seabass (Dicentrarchus labrax). A total of 486 juvenile seabass with an average weight of 90 g were fed six diets containing varied organic proteins. The control group (CON) was fed a diet with conventional fishmeal from sustainable fisheries as the primary protein source. The other five groups were fed diets with different compositions: organic Iberian pig meal byproduct (IB diet), a combination of organic Iberian pig meal byproduct and insect meal (IB-IN diet), a mix of organic Iberian pig meal byproduct and organic rainbow trout meal byproduct (IB-TR diet), a blend of organic rainbow trout meal byproduct and insect meal (TR-IN), and a mixed diet containing all of these protein sources (MIX diet). Over a 125-day feeding trial, growth performance, feed utilisation, feed digestibility, and histological parameters were assessed. The results showed that the fish fed the control diet had the highest final weight and specific growth rate, followed by the fish fed the TR-IN and IB-TR diets. The IB-TR diet had the highest apparent digestibility coefficients (ADCs) for protein, while the TR-IN diet had the lowest. Histological analysis revealed that fish fed the control diet had the largest nucleus diameter and hepatocyte diameter. Use of IN seems to penalise performance in several ways. Fish fed diets containing insect meal grew less, and those diets had lower digestibility. Fish fed the TR and IB diets grew at rates near that of the control, and the feed had acceptable digestibility.

Ferrous Ion Alleviates Lipid Deposition and Inflammatory Responses Caused by a High Cottonseed Meal Diet by Modulating Hepatic Iron Transport Homeostasis and Controlling Ferroptosis in Juvenile Ctenopharyngodon idellus

To investigate the mechanisms through which ferrous ion (Fe2+) addition improves the utilization of a cottonseed meal (CSM) diet, two experimental diets with equal nitrogen and energy content (low-cottonseed meal (LCM) and high-cottonseed meal (HCM) diets, respectively) containing 16.31% and 38.46% CSM were prepared. Additionally, the HCM diet was supplemented with graded levels of FeSO4·7H2O to establish two different Fe2+ supplementation groups (HCM + 0.2%Fe2+ and HCM + 0.4%Fe2+). Juvenile Ctenopharyngodon idellus (grass carps) (5.0 ± 0.5 g) were fed one of these four diets (HCM, LCM, HCM + 0.2%Fe2+ and HCM + 0.4%Fe2+ diets) for eight weeks. Our findings revealed that the HCM diet significantly increased lipid peroxide (LPO) concentration and the expression of lipogenic genes, e.g., sterol regulatory element binding transcription factor 1 (srebp1) and stearoyl-CoA desaturase (scd), leading to excessive lipid droplet deposition in the liver (p < 0.05). However, these effects were significantly reduced in the HCM + 0.2%Fe2+ and HCM + 0.4%Fe2+ groups (p < 0.05). Plasma high-density lipoprotein (HDL) concentration was also significantly lower in the HCM and HCM + 0.2%Fe2+ groups compared to the LCM group (p < 0.05), whereas low-density lipoprotein (LDL) concentration was significantly higher in the HCM + 0.2%Fe2+ and HCM + 0.4%Fe2+ groups than in the LCM group (p < 0.05). Furthermore, the plasma levels of liver functional indices, including alkaline phosphatase (ALP), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and glucose (GLU), were significantly lower in the HCM + 0.4%Fe2+ group (p < 0.05). Regarding the expression of genes related to iron transport regulation, transferrin 2 (tfr2) expression in the HCM group and Fe2+ supplementation groups were significantly suppressed compared to the LCM group (p < 0.05). The addition of 0.4% Fe2+ in the HCM diet activated hepcidin expression and suppressed ferroportin-1 (fpn1) expression (p < 0.05). Compared to the LCM group, the expression of genes associated with ferroptosis and inflammation, including acyl-CoA synthetase long-chain family member 4b (acsl4b), lysophosphatidylcholine acyltransferase 3 (lpcat3), cyclooxygenase (cox), interleukin 1β (il-1β), and nuclear factor kappa b (nfκb), were significantly increased in the HCM group (p < 0.05), whereas Fe2+ supplementation in the HCM diet significantly inhibited their expression (p < 0.05) and significantly suppressed lipoxygenase (lox) expression (p < 0.05). Compared with the HCM group without Fe2+ supplementation, Fe2+ supplementation in the HCM diet significantly upregulated the expression of genes associated with ferroptosis, such as heat shock protein beta-associated protein1 (hspbap1), glutamate cysteine ligase (gcl), and glutathione peroxidase 4a (gpx4a) (p < 0.05), and significantly decreased the expression of the inflammation-related genes interleukin 15/10 (il-15/il-10) (p < 0.05). In conclusion, FeSO4·7H2O supplementation in the HCM diet maintained iron transport and homeostasis in the liver of juvenile grass carps, thus reducing the occurrence of ferroptosis and alleviating hepatic lipid deposition and inflammatory responses caused by high dietary CSM contents.

Infection dynamic of Micropterus salmoides rhabdovirus and response analysis of largemouth bass after immersion infection

Largemouth bass (Micropterus salmoides) is an important economic freshwater aquaculture fish originating from North America. However, the frequent outbreaks of Micropterus salmoides rhabdovirus (MSRV) have seriously limited the healthy development of Micropterus salmoides farming industry. In the present study, a strain of MSRV was isolated and identified from infected largemouth bass by PCR, transmission electron micrograph observation and genome sequences analysis, and tentatively named MSRV-HZ01 strain. Phylogenetic analyses showed that the MSRV-HZ01 presented the highest similarity to MSRV-2021, followed by MSRV-FJ985 and MSRV-YH01. The various tissues of juvenile largemouth bass exhibited significant pathological damage following MSRV-HZ01 immersion infection, and the mortality reached 90%. We also found that intestine was the key organ for MSRV to enter the fish body initially by dynamic analysis of viral infection, and the head kidney was the susceptible tissue of virus. Moreover, the MSRV was also transferred to the external mucosal tissue in later stage of viral infection to achieve horizontal transmission. In addition, the genes of IFN γ and IFN I-C were significantly up-regulated after MSRV infection to exert antiviral functions. The genes of cGAS and Sting might play an important role in the regulation of interferon expression. In conclusion, we investigated the virus infection dynamics and fish response following MSRV immersion infection, which would promote our understanding of the interaction between MSRV and largemouth bass under natural infection.

Effects of Clostridium butyricum on Growth Performance, Intestinal Health, and Disease Resistance of Hybrid Grouper (Epinephelus fuscoguttatus♀ × E. lanceolatus♂) Fed with Cottonseed Protein Concentrate (CPC) Replacement of Fishmeal

An 8-week feeding trial was conducted to investigate the effects of C. butyricum on the growth performance, microbiota, immunity response, and disease resistance in hybrid grouper fed with cottonseed protein concentrate (CPC) replacement of fishmeal. Six groups of isonitrogenous and isolipid diets were formulated including a positive control group (50% fishmeal, PC), a negative control group (CPC replaced 50% of fishmeal protein, NC), and Clostridium butyricum supplemented with 0.05% (C1, 5 × 10⁸ CFU/kg), 0.2% (C2, 2 × 10⁹ CFU/kg), 0.8% (C3, 8 × 10⁹ CFU/kg), and 3.2% (C4, 3.2 × 10¹⁰ CFU/kg), respectively, to the NC group. The results showed that weight gain rate and specific growth rate were significantly higher in the C4 group than that in the NC group (P < 0.05). After supplementation with C. butyricum, the amylase, lipase, and trypsin activities were significantly higher than the NC group (P < 0.05; except group C1), and the same results were obtained for intestinal morphometry. The intestinal proinflammatory factors were significantly downregulated, and the anti-inflammatory factors were significantly upregulated in the C3 and C4 groups compared with the NC group after supplementation with 0.8%-3.2% C. butyricum (P < 0.05). At the phylum level, the PC, NC, and C4 groups were dominated by the Firmicutes and the Proteobacteria. At the genus level, the relative abundance of Bacillus in the NC group was lower than that in the PC and C4 groups. After supplementation with C. butyricum, grouper in the C4 group showed significantly higher resistance to V. harveyi than the NC group (P < 0.05). Above all, taking into account the effects of immunity and disease resistance, it was recommended to supplement 3.2% C. butyricum in the diet of grouper fed the replacement of 50% fishmeal protein by CPC.

Dietary yeast glycoprotein supplementation improves the growth performance, intestinal health and disease resistance of largemouth bass (Micropterus salmoides) fed low-fishmeal diets

The active ingredients extracted from yeast are important for regulating animal health. The aim of the current research was to explore the impacts of dietary yeast glycoprotein (YG) on the growth performance, intestinal morphology, antioxidant capacity, immunity and disease resistance of largemouth bass (Micropterus salmoides). A total of 375 juvenile fish (6.00 ± 0.03 g) were allocated into 15 fiberglass tanks. Triplicate tanks were assigned to each diet. The dietary YG inclusion was as follows: the first group was given a high fishmeal diet (40% fishmeal, 0% YG) (FM) and the second group was given a low fishmeal diet (30% fishmeal and 15% soybean meal, 0% YG) (LFM). The fish in the third, fourth and fifth groups were fed the LFM diet supplemented with 0.5% (LFM+YG0.5), 1.0% (LFM+YG1.0) and 2.0% (LFM+YG2.0) YG, respectively. After a 60- day feeding trial, a challenge test using A. hydrophila was carried out. The results showed that the final body weight (FBW) and weight gain rate (WGR) in the LFM+YG2.0 group were significantly higher than those in the LFM group and were no significantly different from those in the FM group. This may be partially related to the activation of the target of rapamycin (TOR) signaling pathway. Dietary YG supplementation enhanced intestinal physical barriers by upregulating the intestinal tight junction protein related genes (claudin1, occludin and zo2) and improving the structural integrity of the gut, which may be partially associated with AMPK signaling pathway. Moreover, dietary YG increased the antioxidant capacity in the gut, upregulated intestinal anti-inflammatory factors (il-10, il1-1β and tgf-β) and downregulated proinflammatory factors (il-1β and il-8), which may be partially related to the Nrf2/Keap1 signaling pathways. The results of the challenge test indicated that dietary supplementation with 0.5 or 1.0% YG can increase the disease tolerance of largemouth bass against A. hydrophila. In conclusion, the present results indicated that dietary supplementation with YG promotes the growth performance, intestinal immunity, physical barriers and antioxidant capacity of largemouth bass. In addition, 1.0% of dietary YG is recommended for largemouth bass based on the present results.

Effects of Replacing Fishmeal with the Mixture of Cottonseed Protein Concentrate and Clostridium autoethanogenum Protein on the Growth, Nutrient Utilization, Serum Biochemical Indices, Intestinal and Hepatopancreas Histology of Rainbow Trout (Oncorhynchus mykiss)

The purpose of this study was to develop the potential of cottonseed protein concentrate (CPC) and Clostridium autoethanogenum protein (CAP) in the diet of rainbow trout (Oncorhynchus mykiss) by evaluating the effects of substituting fishmeal with a CPC and CAP mixture on growth performance, nutrient utilization, serum biochemical indices, intestinal and hepatopancreas histology. In a basal diet containing 200 g/kg fishmeal (Con), the mixture of CPC and CAP (1:1) was used to reduce dietary fishmeal to 150, 100, 50 and 0 g/kg, to form five diets with the same crude protein and crude lipid contents (CON, FM-15, FM-10, FM-5 and FM-0). Then, the five diets were fed to rainbow trout (35.00 ± 0.05 g) for 8 weeks. The weight gain (WG) and feed conversion ratio (FCR) of the five groups were 258.72%, 258.82%, 249.90%, 242.89%, 236.57%, and 1.19, 1.20, 1.24, 1.28, 1.31, respectively. FM-5 and FM-0 groups showed significantly lower WG and higher FCR than the CON group (p < 0.05). In terms of whole-body composition, such as moisture, crude ash, and crude protein, no significant difference was observed among all the groups (p > 0.05), except that significantly higher crude lipid content was detected in the FM-0 group than in the CON group (p < 0.05). In the FM-5 and FM-0 groups, protein efficiency, protein retention, intestinal protease activity and amylase activity were significantly lower than in the CON group (p < 0.05). Compared to the CON group, the serum contents of glucose and total cholesterol in the FM-0 group as well as MDA in the FM-5 and FM-0 groups were significantly increased, and catalase, superoxide dismutase, and total antioxidant capacity were decreased (p < 0.05). In intestine and hepatopancreas histology, the intestinal villus height in the FM-5 and FM-0 groups and villus width in the FM-0 group were decreased significantly (p < 0.05), while no significant difference in hepatopancreas morphology was observed among all the groups except that some vacuolization was observed in the FM-0 group (p > 0.05). In summary, the mixture of CPC and CAP can effectively replace 100 g/kg fishmeal in a diet containing 200 g/kg fishmeal without adverse effects on the growth performance, nutrient utilization, serum biochemical, or intestinal and hepatopancreas histology of rainbow trout.

Comparative study on the effects of crystalline L-methionine and methionine hydroxy analogue calcium supplementations in the diet of juvenile Pacific white shrimp (Litopenaeus vannamei)

An 8-week feeding trial was conducted to evaluate the effects of L-methionine and methionine hydroxy analogue calcium (MHA-Ca) supplements in low-fishmeal diet on growth performance, hepatopancreas morphology, protein metabolism, anti-oxidative capacity, and immunity of Pacific white shrimp (Litopena eus vannamei). Four isonitrogenous and isoenergetic diets were designed: PC (203.3 g/kg fishmeal), NC (100 g/kg fishmeal), MET (100 g/kg fishmeal +3 g/kg L-methionine) and MHA-Ca (100 g/kg fishmeal +3 g/kg MHA-Ca). White shrimp (initial body weight 0.23 ± 0.00 g, 50 shrimp per tank) were allocated to 12 tanks and divided among 4 treatments in triplicates. In response to L-methionine and MHA-Ca supplementations, the shrimp exhibited higher weight gain rate (WGR), specific growth rate (SGR), condition factor (CF), and lower hepatosomatic index (HSI) compared to those fed the NC diet (p < 0.05). The WGR and SGR of shrimp fed L-methionine and MHA-Ca showed no difference with those in the PC diet (p > 0.05). Both of L-methionine and MHA-Ca supplementary diets significantly decreased the malondialdehyde (MDA) levels of shrimp when compared with the NC diet (p < 0.05). L-methionine supplementation improved the lysozyme (LZM) activity and total antioxidant capacity (T-AOC) of shrimp, while the MHA-Ca addition elevated the reduced glutathione (GSH) levels in comparison with those fed the NC diet (p < 0.05). Hypertrophied blister cells in hepatocytes were observed in shrimp fed the NC diet, and alleviated with L-methionine and MHA-Ca supplementations. Shrimp fed the MET and MHA-Ca diets had higher mRNA expression levels of target of rapamycin (tor) than those fed the NC diet (p < 0.05). Compared to the NC group, dietary MHA-Ca supplementation upregulated the expression level of cysteine dioxygenase (cdo) (p < 0.05), while L-methionine supplementation had no significant impact (p > 0.05). The expression levels of superoxide dismutase (sod) and glutathione peroxidase (gpx) were significantly upregulated by L-methionine supplemented diet in comparison with those in the NC group (p < 0.05). Overall, the addition of both L-methionine and MHA-Ca elevated the growth performance, facilitated protein synthesis, and ameliorated hepatopancreatic damage induced by plant-protein enriched diet in L. vannamei. L-methionine and MHA-Ca supplements enhanced anti-oxidants differently.

An Evaluation of Laminarin Additive in the Diets of Juvenile Largemouth Bass (Micropterus salmoides): Growth, Antioxidant Capacity, Immune Response and Intestinal Microbiota

A 28 day feeding trial was conducted to investigate the growth performance, immune response and intestinal microbiota of laminarin (LAM) supplemented diets in juvenile largemouth bass (Micropterus salmoides). Four hundred and eighty fish (initial average weight: 0.72 ± 0.04 g) were randomly divided into four groups (40 fish per tank with three replicates in each group) Four diets were prepared with LAM supplementation at the doses of 0 (control), 5 g Kg^-1 (LL), 10 g Kg^-1 (ML) and 15 g Kg^-1 (HL), respectively. No significant difference in the specific growth rate (SGR) and hepatosomatic index (HSI) was observed in fish among the four groups, or in the lipid and ash content of fish flesh. In addition, fish in the LL group exhibited much higher antioxidant capacity (p < 0.05), while the diets with the inclusion of 5 and 10 g Kg^-1 LAM remarkably decreased the antioxidant capacity of fish (p > 0.05). Dietary LAM at the dose of 5 g Kg^-1 inhibited the transcription of interleukin-1β (il-1β) and tumor necrosis factor-α (tnf-α), while promoting the expression of transforming growth factor-β (tgf-β) in fish intestine. Moreover, the beneficial intestinal bacteria Bacteroide, Comamonas and Mycoplasma abundance significantly increased in fish from the LL group, while the content of opportunistic pathogens Plesiomonas, Aeromonas and Brevinema in fish of the HL group was substantially higher than the control group. Overall, the appropriate dose of supplemented LAM in the diet was 5 g Kg^-1, while an excessive supplementation of LAM in the diet led to microbial community instability in largemouth bass.

Effects of replacing fishmeal with cottonseed protein concentrate on growth performance, blood metabolites, and the intestinal health of juvenile rainbow trout (Oncorhynchus mykiss)

Cottonseed protein concentrate (CPC) is a potential non-food protein source for fishmeal replacement in fish feed. However, a high inclusion level of CPC in diets may have adverse effects on the metabolism and health of carnivorous fish. This study aimed to investigate CPC as a fishmeal alternative in the diet of rainbow trout Oncorhynchus mykiss based on growth performance, blood metabolites, and intestinal health. Five isonitrogenous (46% crude protein) and isolipidic (16% crude lipid) diets were formulated: a control diet (30% fishmeal) and four experimental diets with substitution of fishmeal by CPC at 25%, 50%, 75%, and 100%. A total of 600 fish (mean body weight 11.24g) were hand-fed the five formulated diets to apparent satiation for eight weeks. The results showed no adverse effects on growth performance when 75% dietary fishmeal was replaced by CPC. However, reduced growth and feed intake were observed in rainbow trout fed a fishmeal-free diet based on CPC (CPC100%). Changes in serum metabolites were also observed in CPC100% compared with the control group, including an increase in alanine aminotransferase (ALT), a decrease in alkaline phosphatase (ALP), alterations in free amino acids, and reductions in cholesterol metabolism. In addition, the CPC-based diet resulted in reduced intestinal trypsin, decreased villus height and width in the distal intestine, upregulated mRNA expression levels of inflammatory cytokines in the intestine, and impaired gut microbiota with reduced bacterial diversity and decreased abundance of Bacillaceae compared with the control group. The findings suggest that the optimum substitution rate of dietary fishmeal by CPC for rainbow trout should be less than 75%.

Effects of Enzymatic Cottonseed Protein Concentrate as a Feed Protein Source on the Growth, Plasma Parameters, Liver Antioxidant Capacity and Immune Status of Largemouth Bass (Micropterus salmoides)

This study appraised the impact of enzymatic cottonseed protein concentrate (ECP) as a fish meal (FM) substitute on the growth and health of largemouth bass (Micropterus salmoides) (initial weight 14.99 ± 0.03 g). Five diets with equal nitrogen, fat, and energy were designed to replace 0%, 7.78%, 15.56%, 23.33%, and 31.11% FM by adding 0%, 3.6%, 7.2%, 10.8%, and 14.4% ECP, named ECP0, ECP3.6, ECP7.2, ECP10.8, and ECP14.4, respectively. We fed 300 fish with five experimental diets for 60 days. The results revealed that weight gain rate (WGR) and specific growth rate (SGR) did not notably reduce until the addition of ECP exceeded 7.2%. The proximate composition of fish was not affected by the amount of ECP added in diets. Plasma total protein (TP), albumin (ALB), and high-density lipoprotein (HDL) concentrations increased with the increase of ECP dosage, while the triglyceride (TG) and low-density lipoprotein (LDL) concentrations and alkaline phosphatase (ALP) activity showed an opposite trend. For hepatic antioxidant capacity, the hepatic total superoxide dismutase (T-SOD) and catalase (CAT) activities, glutathione (GSH) content, and the expression of nuclear factor erythroid 2-related factor 2 (Nrf2), superoxide dismutase (SOD), and CAT were increased by ECP, while the hepatic malondialdehyde (MDA) content and the expression of kelch-like-ECH-associated protein 1 (Keap1) were decreased. With regard to inflammation, the expression of nuclear factor-kappa B (NF-κB), interleukin-8 (IL-8), and tumor necrosis factor-α (TNF-α) were inhibited by ECP. In summary, the amount of ECP added to diet can reach 7.2% to replace 15.56% FM without hampering the growth of largemouth bass, and ECP can improve the antioxidant and immune capacity.

Effect of Autolyzed Yarrowia lipolytica on the Growth Performance, Antioxidant Capacity, Intestinal Histology, Microbiota, and Transcriptome Profile of Juvenile Largemouth Bass (Micropterus salmoides)

The improper components of formulated feed can cause the intestinal dysbiosis of juvenile largemouth bass and further affect fish health. A 28 day feeding trial was conducted to investigate the effect of partially replacing fish meal (FM) with autolyzed Yarrowia lipolytica (YL) on juvenile largemouth bass (Micropterus salmoides). We considered four diets—control, YL25, YL50, and YL75—in which 0%, 25%, 50%, and 75% of the FM content, respectively, was replaced with YL. According to results, the weight gain rate (WGR) and specific growth rate (SGR) of the fish with the YL25 and YL50 diets were significantly higher than the WGR and SGR with the control diet, while the YL75 diet significantly reduced fish growth and antioxidant enzymes activities, and shortened the villus height in the intestinal mucosa. The 16S rRNA analysis of the intestinal microbiota showed that the relative abundance of Mycoplasma was significantly increased with the YL25 and YL50 diets, while the Enterobacteriacea content was increased with the YL75 diet. Moreover, our transcriptome analysis revealed that certain differentially expressed genes (DEGs) that are associated with growth, metabolism, and immunity were modulated by YL inclusion treatment. Dietary YL25 and YL50 significantly reduced the mRNA level of ERBB receptor feedback inhibitor 1 (errfi1) and dual-specificity phosphatases (dusp), while the expression of the suppressor of cytokine signaling 1 (socs1), the transporter associated with antigen processing 2 subunit type a (tap2a), and the major histocompatibility complex class I-related gene (MHC-I-l) were sharply increased with YL75 treatment. We determined that the optimum dose of dietary YL required for maximum growth without any adverse influence on intestinal health was 189.82 g/kg (with 31.63% of the fishmeal replaced by YL), while an excessive substitution of YL for fishmeal led to suppressed growth and antioxidant capacity, as well as intestinal damage for juvenile largemouth bass.

Feed Restriction Alleviates Chronic Thermal Stress-Induced Liver Oxidation and Damages via Reducing Lipid Accumulation in Channel Catfish (Ictalurus punctatus)

Caloric restriction is known to suppress oxidative stress in organ systems. However, whether caloric/feed restriction alleviates chronic thermal stress in aquatic animals remains unknown. Here, we set up three feeding rations: 3% BW (3% body weight/day), 2.5% BW (restricted feeding, 2.5% body weight/day) and 2% BW (high restricted feeding, 2% body weight/day), to investigate the effects and mechanism of feed restriction on improving chronic heat-induced (27 to 31 °C) liver peroxidation and damages in channel catfish (Ictalurus punctatus). The results showed that, compared to 3% BW, both 2.5% BW and 2% BW significantly reduced the liver expressions of hsc70, hsp70 and hsp90, but only 2.5% BW did not reduce the growth performance of channel catfish. The 2.5% BW and 2% BW also reduced the lipid deposition (TG) and improved the antioxidant capacity (CAT, SOD, GSH and T-AOC) in the liver of channel catfish. The heat-induced stress response (plasma glucose, cortisol and NO) and peroxidation (ROS and MDA) were also suppressed by either 2.5% BW or 2% BW. Moreover, 2.5% BW or 2% BW overtly alleviated liver inflammation and damages by reducing endoplasmic reticulum (ER) stress (BIP and Calnexin) and cell apoptosis (BAX, Caspase 3 and Caspase 9) in the liver of channel catfish. In conclusion, 2.5% body weight/day is recommended to improve the antioxidant capacity and liver health of channel catfish during the summer season, as it alleviates liver peroxidation and damages via suppressing lipid accumulation under chronic thermal stress.