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

Soluble trehalase responds to heavy metal stimulation by regulating apoptosis in Neocaridina denticulata sinensis

Trehalase plays an important role in insect metabolism and development by hydrolyzing blood sugar trehalose, but it seems to perform primarily an immunomodulatory function in crustaceans whose blood sugar is glucose. Metal ions as pollutants seriously affecting crustacean health, but studies on trehalase in metal immunity are still limited. In this study, a soluble trehalase (NdTre1) that could bind to multiple metals was identified from Neocaridina denticulata sinensis for investigating metal resistance. Expression profiling revealed that NdTre1 was mainly expressed in the gill and was significantly decreased following stimulation with copper (Cu²⁺) and cadmium (Cd²⁺). Transcriptomic analysis of gills revealed an increase in ecdysone synthesis after interference with NdTre1. Increased ecdysone activated the endogenous mitochondrial pathway and the mitogen activated protein kinase (MAPK) pathway to further induced apoptosis. In vitro, Escherichia coli overexpressing recombinant NdTre1 had higher survival and faster growth rates to better adapted the metal-containing medium. Overall, NdTre1 exercises an important immune function in shrimp resistance to metal stimulation by regulating apoptosis and molting. Further investigation can further explore specific response mechanisms of NdTre1 to multiple metals.

Plantago asiatica seed as a protective agent for mitigating metals toxicity on Penaeusvannamei

Plantago asiatica seeds (PS) are commonly used as a medicinal plant. This study investigates the efficacy of PS against heavy metal toxicity in white shrimp (Penaeus vannamei). After feeding PS diet (5 g/kg) or basal diet (control group) for 7 days, shrimps were exposed to sublethal concentrations of heavy metals in seawater (As: 12 mg/L, Pb: 250 mg/L, Hg: 0.4 mg/L). The 7-day survival observation showed that the survival in groups fed with PS were significantly higher than that in the control group, revealing that dietary PS had the efficacy to mitigate heavy metal toxicity in white shrimp. Under the same feeding condition, white shrimps were exposed to safety dose of heavy metals (1/10 of sublethal concentrations) to understand the mechanism of mitigation. The metal accumulations in haemolymph, gills, hepatopancreas, and muscle tissues as well as the immune, anti-oxidative, stress related gene expressions in haemocytes, gills and hepatopancreas were measured for 14 days. The As accumulation in gills and hepatopancreas of groups fed with PS were significantly lower than those of control group on day 7 and 14, respectively; The Pb concentration in haemolymph of group fed with PS was significantly lower than that of control group on day 7 and 14; The Hg concentration in hepatopancreas of the group fed with PS was significantly lower than that of control group on day 7. Dietary PS could mitigate heavy metal-induced immune suppression, oxidative stress, and stress response by positively regulating immune (proPO I, Toll, IMD), antioxidant (SOD, GST, Trx), and negatively regulating stress response genes (HSP70, MT). The present study demonstrated that dietary PS could protect white shrimp against metal toxicity by reducing metal accumulations and regulating the immune, antioxidant, and stress response gene expressions in specific tissue. Therefore, PS may serve as a beneficial feed additive in the aquaculture.

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.

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.

Prophylactic effects of dietary caper (Capparis spinosa) extracts on the control of Streptococcus agalactiae infection, growth, immune-antioxidant, and inflammation cytokine responses of Nile tilapia fingerlings

The antibacterial activity of aqueous (AE) or ethanolic extracts (EE) of caper (Capparis spinosa) against Streptococcus agalactiae was evaluated in vitro. Both caper extracts showed antagonistic activity against S. agalactiae and the inhibition zones in case of ethanolic extracts were larger than those of aqueous ones. Additionally, TEM investigations show that S. agalactiae cells treated with both C. spinosa extracts were damaged and degraded and this damage was greater in case of ethanolic extract. Another study was done to assess the promotion effects of dietary caper (C. spinosa) extracts on growth, antioxidant and immune activity, and inflammation cytokine responses of Nile tilapia (Oreochromis niloticus) and its resistance to S. agalactiae infection. However, fish (40 ± 2 g) were fed on diets containing 1.0 and 2.0 g/kg feed of each caper extract as well as the control group (free of caper) for 6 weeks. Fish were intraperitoneally injected (IP) with Streptococcus agalactiae at the end of the feeding trial, and fish mortality was tracked for additional ten days. Compared with other treatments, fish fed on 2.0 g EE/kg feed had higher counts of white and red blood cells as well as higher hemoglobin levels accompanied with lower AST and ALT activities. Antioxidant (superoxide dismutase and catalase activities) and immune, total protein, globulin, lysozyme, and immunoglobulin M) indices were increased along with significant decline in MDA levels in both caper extracts treated fish groups compared to the control group. Significant promotion in fish growth was affected positively with the increase in both caper extracts; particularly, the larger fish growth was observed in the treatment of 2.0 g EE/kg feed. Expressions of IL-1β and IL-8 were declined; meanwhile levels of IL-10, SOD and CAT genes were upregulated in fish fed on 2.0 g EE/kg feed compared to other groups. After being challenged with S. agalactiae infection, fish survival was considerably (P < 0.05) greater in fish groups that fed on diets with caper extracts; particularly 2.0 g EE/kg feed (75%); while all fish fed on the control one were dead. According to these findings, the antioxidant and immune response of Nile tilapia fingerlings is stimulated by ethanolic extract of caper (2.0 g/kg feed), which also enhanced the growth performance and fish resistance to S. agalactiae infection.

Using Azadirachta indica protein hydrolysate as a plant protein in Nile tilapia (Oreochromis niloticus) diet: Effects on the growth, economic efficiency, antioxidant-immune response and resistance to Streptococcus agalactiae

A feeding trial for 90 days was conducted on Nile tilapia (Oreochromis niloticus) (average weight: 25.50 ± 0.05 g) to evaluate the effect of dietary inclusion of Azadirachta indica seed protein hydrolysate (AIPH). The evaluation included the impact on the growth metrics, economic efficiency, antioxidant potential, hemato-biochemical indices, immune response, and histological architectures. A total of 250 fish were randomly distributed in five treatments (n = 50) and received diets included with five levels of AIPH (%): 0 (control diet, AIPH0), 2 (AIPH2), 4 (AIPH4), 6 (AIPH6) or 8 (AIPH8), where AIPH partially replace fish meal by 0, 8.7%, 17.4%, 26.1%, and 34.8%, respectively. After the feeding trial, a pathogenic bacterium (Streptococcus agalactiae, 1.5 × 108 CFU/mL) was intraperitoneally injected into the fish and the survival rate was recorded. The results elucidated that AIPH-included diets significantly (p < 0.05) enhanced the growth indices (final body weight, total feed intake, total body weight gain, and specific growth rate) and intestinal morpho-metrics (villous width, length, muscular coat thickness, and goblet cells count) in comparison to the control diet, with the AIPH8 diet recording the highest values. Dietary AIPH inclusion significantly improved (p < 0.05) the economic efficacy indicated by reduced feed cost/kg gain and increased performance index. The fish fed on the AIPH diets had noticeably significantly higher (p < 0.05) protein profile variables (total proteins and globulin) and antioxidant capabilities (superoxide dismutase and total antioxidant capacity) than the AIPH0 group. The dietary inclusion of AIPH significantly (p < 0.05) boosted the haematological parameters (haemoglobin, packed cell volume %, and counts of red blood cells and white blood cells) and immune indices (serum bactericidal activity %, antiprotease activity, and immunoglobulin M level) in a concentration-dependent manner. The blood glucose and malondialdehyde levels were significantly (p < 0.05) lowered by dietary AIPH (2%-8%). The albumin level and hepatorenal functioning parameters (aspartate aminotransferase, alanine aminotransferase, and creatinine) were not significantly (p > 0.05) altered by AIPH diets. Additionally, AIPH diets did not adversely alter the histology of the hepatic, renal or splenic tissues with moderately activated melano-macrophage centres. The mortality rate among S. agalactiae-infected fish declined as dietary AIPH levels rose, where the highest survival rate (86.67%) was found in the AIPH8 group (p < 0.05). Based on the broken line regression model, our study suggests using dietary AIPH at the optimal level of 6%. Overall, dietary AIPH inclusion enhanced the growth rate, economic efficiency, health status, and resistance of Nile tilapia to the S. agalactiae challenge. These beneficial impacts can help the aquaculture sector to be more sustainable.