Dietary Chlorella vulgaris modulates the performance, antioxidant capacity, innate immunity, and disease resistance capability of Nile tilapia fingerlings fed on plant-based diets

Harnessing the fish gut microbiome and immune system to enhance disease resistance in aquaculture

The increasing global reliance on aquaculture is challenged by disease outbreaks, exacerbated by antibiotic resistance, and environmental stressors. Traditional strategies, such as antibiotic treatments and chemical interventions, are becoming less effective, necessitating a shift toward microbiota-based disease control. The fish gut microbiome is a key determinant of immune homeostasis and pathogen resistance. However, previous reviews lack integration of microbiome engineering, machine learning, and next-generation sequencing in fish health strategies. This review encompasses recent advancements in microbiome research, including dietary strategies such as prebiotics, probiotics, synbiotics, and phytogenic feed additives. It synthesizes the latest metagenomic insights, microbiota modulation techniques, and AI-driven disease prediction models. It presents a novel conceptual framework for disease control using microbiome-based approaches in aquaculture. Additionally, we explore emerging methodologies, including microbiota transplantation and synthetic probiotics, to develop precision microbiome interventions. By bridging existing knowledge gaps, this review provides actionable insights into sustainable aquaculture practices through microbiome-driven disease resistance.

Chlorella vulgaris as a Livestock Supplement and Animal Feed: A Comprehensive Review

This review explores the potential of Chlorella vulgaris (CLV) as an alternative supplement in animal feed. CLV is rich in essential nutrients including fatty acids, amino acids, vitamins, and minerals, as well as bioactive compounds such as antioxidants, which contribute to its health-promoting properties. The nutritional composition of CLV can vary depending on factors such as cultivation methods, nutrient availability, light intensity, temperature, water pH, strain, and processing techniques. The rigid cell wall of the microalga limits nutrient accessibility, particularly in monogastric animals. However, processing techniques such as enzymatic treatments can disrupt the cell wall, enhancing nutrient bioavailability and improving its utility as a feed ingredient. Research across livestock species has demonstrated the positive effects of CLV supplementation. For instance, CLV has improved milk production and composition in ruminants, modulated rumen microbiota, enhanced lamb growth, and elevated blood immunoglobulin levels. Moreover, the impact of CLV on ruminal fermentation is dose-dependent, with higher inclusion rates exhibiting more pronounced effects, and it may also play a role in mitigating methane emissions. In poultry, CLV supplementation leads to better growth, feed conversion ratios, immune responses, and meat and egg quality. Similarly, studies on pigs suggest that CLV can benefit immune response and fatty acid profiles, while in rabbits, CLV has been found to reduce oxidative stress and improve immune responses. Additionally, CLV has shown promise in aquaculture, improving feed utilization, immunity, and disease resistance in various fish species. While CLV shows considerable potential, the variability in animal responses and the need for optimized inclusion levels necessitate further species-specific research to elucidate the long-term implications of its inclusion in animal diets.

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 ± 0.22 g/fish) for 8 weeks. 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.

Microalgal metabolic engineering facilitates precision nutrition and dietary regulation

Microalgae have gained considerable attention as promising candidates for precision nutrition and dietary regulation due to their versatile metabolic capabilities. This review innovatively applies system metabolic engineering to utilize microalgae for precision nutrition and sustainable diets, encompassing the construction of microalgal cell factories, cell cultivation and practical application of microalgae. Manipulating the metabolic pathways and key metabolites of microalgae through multi-omics analysis and employing advanced metabolic engineering strategies, including ZFNs, TALENs, and the CRISPR/Cas system, enhances the production of valuable bioactive compounds, such as omega-3 fatty acids, antioxidants, and essential amino acids. This work begins by providing an overview of the metabolic diversity of microalgae and their ability to thrive in diverse environmental conditions. It then delves into the principles and strategies of metabolic engineering, emphasizing the genetic modifications employed to optimize microalgal strains for enhanced nutritional content. Enhancing PSY, BKT, and CHYB benefits carotenoid synthesis, whereas boosting ACCase, fatty acid desaturases, and elongases promotes polyunsaturated fatty acid production. Here, advancements in synthetic biology, evolutionary biology and machine learning are discussed, offering insights into the precision and efficiency of metabolic pathway manipulation. Also, this review highlights the potential impact of microalgal precision nutrition on human health and aquaculture. The optimized microalgal strains could serve as sustainable and cost-effective sources of nutrition for both human consumption and aquaculture feed, addressing the growing demand for functional foods and environmentally friendly feed alternatives. The tailored microalgal strains are anticipated to play a crucial role in meeting the nutritional needs of diverse populations and contributing to sustainable food production systems.

Biotransformation of aquaculture wastewater into aquatic feed protein source: Chlorella sorokiniana nutritional value and safety risk assessment

Aquaculture wastewater contains high concentrations of nitrogen and phosphorus compounds, which can be used as nutrients for microalgal growth. In this study, the ability of Chlorella sorokiniana (C. sorokiniana) to purify aquaculture wastewater from an intensive recirculating aquaculture system (RAS) carp sp. farm was evaluated. We then assessed the safety risk of C. sorokiniana cultured from aquaculture wastewater and conducted an 8-week fish feeding trial to evaluate its nutritional value as a feed protein source. The three diets were supplemented with 0 (FM, control), 5% (MM5) or 15% (MM15) C. sorokiniana to replace the fish meal. A total of 180 healthy gibel carp (Carassius gibelio) of similar size were randomly selected into 9 tanks (20 fish/tank, 3 tanks/group). At the end of C. sorokiniana purifying aquaculture wastewater, DIC and DTC gradually decreased by 80.6% and 16.5%, respectively, whereas DOC increased by 52.2%. The change curve of CODMn was similar to that of DOC, and the removal rates of NH4-N, DTN, DIP and DTP were 93.5%, 86.8%, 36.0% and 26.6%, respectively. The heavy metals and antibiotics contents of C. sorokiniana were low or not detected and conformed to the requirements of the aquatic feed ingredient standards. The ARA, EPA and total polyunsaturated fatty acids contents of C. sorokiniana were 13.67, 33.82 and 76.81% of the total fatty acids content, respectively. At the end of the fish feeding trial, we found that the replacement of fishmeal with C. sorokiniana did not affect the growth of the fish or the amino acids contents of the muscle but promoted the body colour values of the fish and the relative content of n-3 polyunsaturated fatty acids in the muscle. In addition, 5% dietary C. sorokiniana can upregulate the relative expression of cat and increase the activity of CAT in the liver; upregulate the relative expression of the proinflammatory factor inf-γ and the anti-inflammatory factors il-4 and tgf-β; and reduce the relative abundance of pathogenic bacteria, such as Citrobacter, Staphylococcus and Pseudomonas, in the gut of gibel carp. However, 15% dietary C. sorokiniana significantly increased the relative expression of inf-γ and hsp70 in the liver and only reduced the relative abundance of Citrobacter. Overall, C. sorokiniana has the ability to remove nutrients from aquaculture wastewater and can be an alternative protein source for fish. On the basis of growth performance, antioxidant capacity, fatty acid contents of muscle, and the gut microbiota, 5% dietary C. sorokiniana is recommended.

Dietary Chlorella vulgaris supplementation modulates health, microbiota and the response to oxidative stress of Atlantic salmon

Microalgae are emerging as functional feed ingredients in aquaculture due to their immune-stimulating and stress-modulating properties. We investigated the potential of the microalgae Chlorella vulgaris as a feed supplement to improve the health and modulate microbiota and stress responses of Atlantic salmon. Triplicate groups of Atlantic salmon (~ 126 g) were reared in a recirculating aquaculture system (RAS) at 15 °C and received diets supplemented with 2% (CV2) or 14% (CV14) spray-dried C. vulgaris daily, 14% once weekly (CV14w), or a control diet (CD) for 8 weeks. Subsequently, all groups were exposed to an acute one-hour peracetic acid (CH3CO3H; PAA) treatment, a commonly used disinfectant in RAS. While CV14 increased feed conversion (FCR) significantly, feeding the diets CV2 and CV14w improved protein retention efficiency. CV14 significantly modulated beta-diversity in the intestinal digesta and mucosa, but this effect was already visible in fish fed CV2. Feeding CV14 and, to a lesser degree, CV2 increased the relative abundances of Paenarthrobacter and Trichococcus in the digesta and mucosa, which are able to metabolize complex carbohydrates. However, the same diets reduced the abundance of the lactic acid bacteria Lactobacillus and Weissella in the digesta and Floricoccus in the mucosa. Peracetic acid exposure induced systemic stress (increase in plasma glucose and cortisol) and a local immune response in the gill, with the most prominent upregulation of several immune- and stress-regulated genes (clra, cebpb, marco, tnfrsf14, ikba, c1ql2, drtp1) 18 h after exposure in fish fed the control diet. Fish receiving CV14 once a week showed a reduced transcriptional response to PAA exposure. Catalase protein abundance in the liver increased following exposure to PAA, while superoxide dismutase abundance in the gill and liver was increased in response to C. vulgaris inclusion before stress. Overall, the results highlight that a high (14%) inclusion rate of C. vulgaris in feed for Atlantic salmon impairs feed conversion and shifts the intestinal microbiota composition in digesta and mucosa. Weekly feeding of C. vulgaris proves a viable approach in improving protein retention and improving transcriptional resilience towards oxidative stress in increasingly intensive production systems. Thereby this study may motivate future studies on optimizing temporal feeding schedules for health-promoting aquafeeds.

Combined intestinal microbiota and transcriptomic analysis to investigate the effect of different stocking densities on the ability of Pacific white shrimp (Litopenaeus vannamei) to utilize Chlorella sorokiniana

Aiming to investigate the impact of different stocking densities on the ability of Pacific white shrimp (Litopenaeus vannamei) to utilize Chlorella sorokiniana (CHL), a 3 × 2 factorial design stocking experiment was used in this study. Specifically, shrimp was fed with two dietary protein sources (fishmeal [FM] and CHL) at low (LSD; 100 per m3), medium (MSD; 200 per m3) and high (HSD; 300 per m3) stocking densities for 8 weeks. The growth performance and resistance to Vibrio parahaemolyticus (1.0 × 107 CFU/mL) of shrimp decreased with the increase of stocking density, but dietary CHL improved this result. Differences between the CHL and FM groups for V. parahaemolyticus resistance were significant only under high-density conditions (P < 0.05). Significant interactions between stocking density and protein source were found on the activities of catalase (CAT), superoxide dismutase (SOD) and phenol oxidase (PO), and the contents of malondialdehyde (MDA) in the hepatopancreas and the activities of intestinal amylase, most of which were significantly different between CHL and FM groups only at high stocking density (P < 0.05). Analysis of 16S rDNA sequencing showed that dietary CHL increased the alpha diversity of intestinal microbiota, inhibited the colonization of pathogenic bacteria and enhanced the abundance of beneficial bacteria. Transcriptomic results showed that at high stocking densities, differentially expressed genes (DEGs) in the FM vs CHL group were mostly upregulated and primarily enriched in immune and metabolic related pathways including Toll, immune deficiency (Imd) and glycolysis-gluconeogenesis pathways. Pearson correlation analysis revealed significant correlation between the top ten intestinal bacteria at the genus level and markedly enriched DEGs, also more were detected under high density situations. In conclusion, CHL has great potential as a novel protein source in the intensive farming of shrimp.

Dietary effects of microalga Tetraselmis suecica on growth, antioxidant-immune activity, inflammation cytokines, and resistance of Nile tilapia fingerlings to Aeromonas sobria infection

The dietary effects of the green microalga Tetraselmis suecica (TS) on the growth, digestive enzymes, immune and antioxidant responses, genes expression, and disease resistance of Nile tilapia (Oreochromis niloticus) fingerlings were investigated. This microalga was mixed with the diet' ingredients at doses of 0.0 (the control), 5, 10, 15, and 20 g/kg diet and then fed to fish daily for 84 days. After the feeding trial, fish were experimentally challenged with Aeromonas sobria, infection and fish mortalities were recorded for another 10 days. Dietary TS significantly (p < 0.05) enhanced growth, digestive enzymes activities, and blood proteins, particularly at the level of 15 g/kg diet. Feeding the fish on 15 TS/kg feed exhibited highest mRNA expressions of GH and IGF-1 genes as well as SOD, CAT, and GPx genes compared to other TS groups. Moreover, highest levels of hepatic antioxidant and immune indices were found in the treatment of 15 g TS/kg feed. Significant downregulation of IL-1β and IL-8 genes expression and significant upregulation of IL-10 gene expression were observed in TS-fed fish, principally in fish groups fed on 15-20 g TS/kg feed. Conversely, hepatic malondialdehyde levels, blood glucose, and the activities of transaminases (ALT and AST) were significantly (p < 0.05) decreased in fish fed with 15-20 g TS/kg diet. Serum bactericidal activity against A. sobria was significantly higher in TS-fed fish groups, and its highest levels were found in treatments of 15-20 g/kg diet. Of interest, the survival rates of fish groups fed diets with 10-20 g TS/kg feed were higher after the challenge with A. sobria infection than the control group. Accordingly, we can conclude that supplementing fish diets with a 15 g TS/kg diet enhanced the growth, antioxidant and immune activities, and resistance of Nile tilapia fingerlings to possible A. sobria infection.

Acrylamide exposure induces growth retardation, neurotoxicity, stress, and immune/antioxidant disruption in Nile tilapia (Oreochromis niloticus): The alleviative effects of Chlorella vulgaris diets

This study looked at the toxic impacts of water-born acrylamide (ACR) on Nile tilapia (Oreochromis niloticus) in terms of behaviors, growth, immune/antioxidant parameters and their regulating genes, biochemical indices, tissue architecture, and resistance to Aeromonas hydrophila. As well as the probable ameliorative effect of Chlorella vulgaris (CV) microalgae as a feed additive against ACR exposure was studied. The 96-h lethal concentration 50 of ACR was investigated and found to be 34.67 mg/L for O. niloticus. For the chronic exposure study, a total of 180 healthy O. niloticus (24.33 ± 0.03 g) were allocated into four groups in tri-replicates (15 fish/replicate), C (control) and ACR groups were fed a basal diet and exposed to 0 and 1/10 of 96-h LC50 of ACR (3.46 mg/L), respectively. ACR+ CV5 and ACR+ CV10 groups were fed basal diets with 5 % and 10 % CV supplements, respectively and exposed to 1/10 of 96-h LC50 of ACR for 60 days. After the exposure trial (60 days) the experimental groups were challenged with A. hydrophila. The findings demonstrated that ACR exposure induced growth retardation (P˂0.01) (lower final body weight, body weight gain, specific growth rate, feed intake, protein efficiency ratio, final body length, and condition factor as well as higher feed conversion ratio). A substantial decrease in the immune/antioxidant parameters (P˂0.05) (lysozyme, serum bactericidal activity %, superoxide dismutase, and reduced glutathione) and neurotransmitter (acetylcholine esterase) (P˂0.01) was noticed with ACR exposure. A substantial increase (P˂0.01) in the serum levels of hepato-renal indicators, lipid peroxidation biomarker, and cortisol was noticed as a result of ACR exposure. ACR exposure resulted in up-regulation (P˂0.05) of the pro-inflammatory cytokines and down-regulation (P˂0.05) of the antioxidant-related gene expression. Furthermore, the hepatic, renal, brain, and splenic tissues were badly affected by ACR exposure. ACR-exposed fish were more sensitive to A. hydrophila infection and recorded the lowest survival rate (P˂0.01). Feeding the ACR-exposed fish with CV diets significantly improved the growth and immune/antioxidant status, as well as modulating the hepatorenal functions, stress, and neurotransmitter level compared to the exposed-non fed fish. In addition, modulation of the pro-inflammatory and antioxidant-related gene expression was noticed by CV supplementation. Dietary CV improved the tissue architecture and increased the resistance to A. hydrophila challenge in the ACR-exposed fish. Noteworthy, the inclusion of 10 % CV produced better results than 5 %. Overall, CV diets could be added as a feed supplement in the O. niloticus diet to boost the fish's health, productivity, and resistance to A. hydrophila challenge during ACR exposure.

Chlorella vulgaris extract conjugated magnetic iron nanoparticles in nile tilapia (Oreochromis niloticus): Growth promoting, immunostimulant and antioxidant role and combating against the synergistic infection with Ichthyophthirius multifiliis and Aeromonashydrophila

Nile tilapia reared under intensive conditions was more susceptible for Ichthyophthirius multifilii (I. multifiliis) infection eliciting higher mortality, lower productive rate and further bacterial coinfection with Aeromonas hydrophila (A. hydrophila). The higher potency of magnetic field of iron oxide nanoparticles (NPs) can kill pathogens through inhibiting their viability. Herein, coating of Chlorella vulgaris extract (ChVE) with magnetic iron oxide NPs (Mag iron NPs) can create an external magnetic field that facilitates their release inside the targeted tissues. Thus, the current study is focused on application of new functionalized properties of Mag iron NPs in combination with ChVE and their efficacy to alleviate I. multifiliis and subsequent infection with A. hydrophila in Nile tilapia. Four hundred fingerlings were divided into: control group (with no additives), three groups fed control diet supplemented with ChVE, Mag iron NPs and ChVE@Mag iron NPs for 90 days. At the end of feeding trial fish were challenged with I. multifiliis and at 9 days post challenge was coinfected by A. hydrophila. A remarkable higher growth rate and an improved feed conversion ratio were detected in group fed ChVE@Mag iron-NPs. The maximum expression of antioxidant enzymes in skin and gills tissues (GSH-Px, CAT, and SOD) which came in parallel with higher serum activities of these enzymes was identified in groups received ChVE@Mag iron-NPs. Furthermore, group fed a combination of ChVE and Mag iron-NPs showed a boosted immune response (higher lysozyme, IgM, ACH50, and MPO) prior to challenge with I. multifiliis. In contrast, fish fed ChVE@Mag iron-NPs supplemented diet had lower infection (decreased by 62%) and mortality rates (decreased by 84%), as well as less visible white spots (decreased by 92 % at 12 dpi) on the body surfaces and mucous score. Interestingly, post I. multifiliis the excessive inflammatory response in gill and skin tissues was subsided by feeding on ChVE@Mag iron-NPs as proved by down regulation of IL-1β, TNFα, COX-2 and iNOS and upregulation of IL-10, and IgM, IgT and Muc-2 genes. Notably, group exposed to I. multifiliis-showed higher mortality when exposed to Aeromonas hydrophilia (increased by 43 %) while group fed ChVE@Mag iron-NPs exhibited lower morality (2%). Moreover, the bacterial loads of A. hydrophilia in fish infected by I. multifiliis and fed control diet were higher than those received dietary supplement of ChVE, Mag iron-NPs and the most reduced load was obtained in group fed ChVE@Mag iron-NPs at 7 dpi. In conclusion, ChVE@Mag iron-NPs fed fish had stronger immune barrier and antioxidant functions of skin and gills, and better survival following I. multifiliis and A. hydrophilia infection.

Dietary Supplementation of Chlorella vulgaris Effectively Enhanced the Intestinal Antioxidant Capacity and Immune Status of Micropterus salmoides

An M. salmoides fish meal diet was supplemented with 0 (CHL0, Control), 38 (CHL38), 76 (CHL76), 114 (CHL114), and 152 (CHL152) mg/kg C. vulgaris for 60 days, and their serum and intestinal samples were analyzed. The results showed that the albumin (ALB) and total protein (TP) contents were observably enhanced in the CHL76 group compared with the Control group. The intestinal glutathione (GSH) and glutathione peroxidase (GSH-Px) contents were enhanced significantly in the CHL76 group, while the total antioxidant capacity (T-AOC) was enhanced in the CHL38 group, compared with the Control group. However, supplementation of >76 g/kg C. vulgaris significantly inhibited the superoxide dismutase (SOD) activity in the intestines of M. salmoides. Moreover, the malondialdehyde (MDA) content was observably dropped in the CHL-supplemented groups compared with the Control group. Transcriptome analysis of the CHL76 and Control groups displayed a total of 1384 differentially expressed genes (DEGs). KEGG analysis revealed that these DEGs were enriched in apoptosis, cytokine-cytokine receptor interaction, tight junction (TJ), and phagosome signaling pathways, which were associated with improved intestinal immunity in the CHL76 group. Additionally, the DEGs enriched in the above pathways were also correlated with the antioxidant parameters, such as catalase (CAT), GSH, GSH-Px, SOD, T-AOC, and MDA. Therefore, our study found that dietary supplementation of C. vulgaris effectively enhanced the intestinal antioxidant capacity of M. salmoides by increasing antioxidant enzyme activity and decreasing MDA content. Additionally, dietary supplementation of C. vulgaris improved the intestinal immune status of M. salmoides by reducing proapoptotic and proinflammatory factors, increasing intestinal TJs- and phagosome-related genes expressions, and increasing the serum ALB and TP contents. Lastly, quadratic regression analysis of the serum biochemical indices (ALB and TP) and intestinal antioxidant parameters (GSH-Px and GSH) revealed that the optimal supplemental level of C. vulgaris in the M. salmoides diet was 58.25-77.7 g/kg.

Dietary Chlorella vulgaris effectively alleviates oxidative stress, immunosuppression, and enhances the resistance to Streptococcus agalactiae infection in cadmium-intoxicated Nile tilapia fingerlings

Aquatic pollutants, including cadmium (Cd), cause oxidative stress on aquatic animals. The use of probiotics, including microalgae as a feed additive to alleviate the toxic impacts of heavy metals, is a much more interesting point. Hence, the current study investigated the oxidative stress and immunosuppression in Nile tilapia (Oreochromis niloticus) fingerlings caused by Cd toxicity as well as the preventive function of dietary Chlorella vulgaris against Cd toxicity. Accordingly, fish were fed on 0.0 (control), 5, and 15 g/kg diet of Chlorella up to satiation thrice a day, along with being exposed to 0.0 or 2.5 mg Cd/L for 60 days. Following the experimental procedure, fish from each group were intraperitoneally injected with Streptococcus agalactiae, and their survivability was observed for further ten days. Chlorella-supplemented diets meaningfully (P < 0.05) boosted the antioxidative capability of fish, which was evidenced by higher activities of hepatic superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione-S-transferase (GST) as well as higher levels of reduced glutathione (GSH) along with significant reductions in hepatic malondialdehyde levels. Moreover, the innate immunity indices [phagocytic activity (PA), respiratory burst activity (RBA), and alternative complement activity (ACH50)] were significantly higher in Chlorella-fed fish, particularly in the group of 15 g/kg diet. Additionally, serum of Chlorella-fed fish showed potent bactericidal activities against S. agalactiae, particularly at the treatment of a 15 g/kg diet. Feeding Chlorella diets to Nile tilapia fingerlings upregulated SOD, CAT, and GPx genes expression alongside the down-regulation of IL-1β, IL-8, IL-10, TNF-α, and HSP70 genes expression. Conversely, Cd toxicity caused oxidative stress and suppressed the fish's innate immunity with upregulation of the expression of IL-1β, IL-8, IL-10, TNF-α, and HSP70 genes. Feeding Cd-exposed fish on Chlorella-containing diets attenuated these adverse effects. The current research revealed that supplementing feeds with the treatment of 15 g/kg diet of C. vulgaris supports the antioxidant-immune responses and alleviates the Cd toxicity effects on Nile tilapia fingerlings.

The Effect of the Microalgae Chlorella vulgaris on the Gut Microbiota of Juvenile Nile Tilapia (Oreochromis niloticus) Is Feeding-Time Dependent

Chlorella vulgaris is one of the most commonly used microalgae in aquaculture feeds. It contains high concentrations of various kinds of nutritional elements that are involved in the physiological regulation of aquaculture animals. However, few studies have been conducted to illustrate their influence on the gut microbiota in fish. In this work, the gut microbiota of Nile tilapia (Oreochromis niloticus) (average weight is 6.64 g) was analyzed by high-throughput sequencing of the 16S rRNA gene after feeding with 0.5% and 2% C. vulgaris additives in diets for 15 and 30 days (average water temperature was 26 °C). We found that the impact of C. vulgaris on the gut microbiota of Nile tilapia was feeding-time dependent. Only by feeding for 30 days (not 15 days) did the addition of 2% C. vulgaris to diets significantly elevate the alpha diversity (Chao1, Faith pd, Shannon, Simpson, and the number of observed species) of the gut microbiota. Similarly, C. vulgaris exerted a significant effect on the beta diversity (Bray-Curtis similarity) of the gut microbiota after feeding for 30 days (not 15 days). During the 15-day feeding trial, LEfSe analysis showed that Paracoccus, Thiobacillus, Dechloromonas, and Desulfococcus were enriched under 2% C. vulgaris treatment. During the 30-day feeding trial, Afipia, Ochrobactrum, Polymorphum, Albidovulum, Pseudacidovorax, and Thiolamprovum were more abundant in 2% C. vulgaris-treated fish. C. vulgaris promoted the interaction of gut microbiota in juvenile Nile tilapia by increasing the abundance of Reyranella. Moreover, during the feeding time of 15 days, the gut microbes interacted more closely than those during the feeding time of 30 days. This work will be valuable for understanding how C. vulgaris in diets impacts the gut microbiota in fish.

Royal Jelly and Chlorella vulgaris Mitigate Gibberellic Acid-Induced Cytogenotoxicity and Hepatotoxicity in Rats via Modulation of the PPARα/AP-1 Signaling Pathway and Suppression of Oxidative Stress and Inflammation

Gibberellic acid (GA3) is a well-known plant growth regulator used in several countries, but its widespread use has negative effects on both animal and human health. The current study assesses the protective effect of royal jelly (RJ) and Chlorella vulgaris (CV) on the genotoxicity and hepatic injury induced by GA3 in rats. Daily oral administration of 55 mg/kg GA3 to rats for 6 constitutive weeks induced biochemical and histopathological changes in the liver via oxidative stress and inflammation. Co-administration of 300 mg/kg RJ or 500 mg/kg CV with GA3 considerably ameliorated the serum levels of AST (aspartate aminotransferase), ALT (alanine aminotransferase), ALP (alkaline phosphatase), γGT (gamma-glutamyl transferase), total bilirubin, and albumin. Lowered malondialdehyde, tumor necrosis factor α (TNF-α), and nuclear factor κB (NF-κB) levels along with elevated SOD (superoxide dismutase), CAT (catalase), and GPx (glutathione peroxidase) enzyme activities indicated the antioxidant and anti-inflammatory properties of both RJ and CV. Also, they improved the histological structure and reduced cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) expressions along with up-regulating peroxisome proliferator activated receptor α (PPARα) and down-regulating activator protein 1 (AP-1) gene expression. Additionally, chromosomal abnormalities and mitotic index were nearly normalized after treatment with RJ and CV. In conclusion, RJ and CV can protect against GA3-induced genotoxicity and liver toxicity by diminishing oxidative stress and inflammation, and modulating the PPARα/AP-1 signaling pathway.

Multi-omics approach to study the dual effects of novel proteins on the intestinal health of juvenile largemouth bass (Micropterus salmoides) under an alternate feeding strategy

Introduction

In an effort to minimize the usage of fishmeal in aquaculture, novel protein diets, including Tenebrio molitor, cottonseed protein concentrate, Clostridium autoethanogenum, and Chlorella vulgaris were evaluated for their potential to replace fishmeal. Nevertheless, comprehensive examinations on the gut health of aquatic animals under an alternate feeding strategy when fed novel protein diets are vacant.

Methods

Five isonitrogenous and isolipidic diets containing various proteins were manufactured, with a diet consisting of whole fishmeal serving as the control and diets containing novel proteins serving as the experimental diets. Largemouth bass (Micropterus salmoides) with an initial body weight of 4.73 ± 0.04g employed as an experimental animal and given these five diets for the first 29 days followed by a fishmeal diet for the next 29 days.

Results

The results of this study demonstrated that the growth performance of novel protein diets in the second stage was better than in the first stage, even though only the C. vulgaris diet increased antioxidant capacity and the cottonseed protein concentrate diet decreased it. Concerning the intestinal barriers, the C. autoethanogenum diet lowered intestinal permeability and plasma IL-1β/TNF-α. In addition, the contents of intestinal immunological factors, namely LYS and sIgA-like, were greater in C. vulgaris than in fishmeal. From the data analysis of microbiome and metabolome, the levels of short chain fatty acids (SCFAs), anaerobic bacteria, Lactococcus, and Firmicutes were significantly higher in the C. autoethanogenum diet than in the whole fishmeal diet, while the abundance of Pseudomonas, aerobic bacteria, Streptococcus, and Proteobacteria was lowest. However, no extremely large differences in microbiota or short chain fatty acids were observed between the other novel protein diets and the whole fishmeal diet. In addition, the microbiota were strongly connected with intestinal SCFAs, lipase activity, and tight junctions, as shown by the Mantel test and Pearson's correlation.

Discussion

Taken together, according to Z-score, the ranking of advantageous functions among these protein diets was C. autoethanogenum diet > C. vulgaris diet > whole fishmeal diet > cottonseed protein concentrate > T. molitor diet. This study provides comprehensive data illustrating a mixed blessing effect of novel protein diets on the gut health of juvenile largemouth bass under an alternate feeding strategy.

Addition of Chlorella sorokiniana meal in the diet of juvenile rainbow trout (Oncorhynchus mykiss): Influence on fish growth, gut histology, oxidative stress, immune response, and disease resistance against Aeromonas salmonicida

This study aimed to assess the effects of dietary addition with Chlorella sorokiniana on fish growth, gut histology, antioxidant capacity, immune response, and disease resistance in rainbow trout. Three diets with similar proximate composition and different Chlorella meal levels were formulated. The control diet, 5% Chlorella diet, and 10% Chlorella diet contained 0%, 5% Chlorella meal, and 10% Chlorella meal, respectively. Each diet was assigned to triplicate tanks containing 30 fish (165.3 ± 0.6 g) in each tank. Fish were fed experimental diets for ninety days. The results showed that the addition of 5% Chlorella in the diet significantly increased feed intake by 19.3% and weight gain rate by 17.3% (P < 0.05) without affecting feed efficiency and gut histology. Diets containing Chlorella meal significantly decreased malonaldehyde contents in the plasma after the lipopolysaccharide (LPS) challenge (P < 0.05). Dietary supplementation with Chlorella meal significantly increased lysozyme (LZM) activity levels (in the head kidney) and immunoglobulin M (IgM) (in the head kidney) and complement component 3 (C3) (in the spleen) contents before the LPS challenge, and simultaneously increased LZM activity levels (in the plasma) and C3 contents (in the plasma and head kidney) after the LPS challenge (P < 0.05). Furthermore, dietary administration of Chlorella meal significantly increased the survival rate of fish infected with Aeromonas salmonicida (P < 0.05). In conclusion, C. sorokiniana can be used to improve fish growth, antioxidant capacity, and immunity.