Zebrafish larvae acute toxicity test: A promising alternative to the fish acute toxicity test

A comprehensive review on probiotics and their use in aquaculture: Biological control, efficacy, and safety through the genomics and wet methods

Probiotics, defined as viable microorganisms that enhance host health when consumed through the diet, exert their effects through mechanisms such as strengthening the immune system, enhancing resistance to infectious diseases, and improving tolerance to stressful conditions. Driven by a growing market, research on probiotics in aquaculture is a burgeoning field. However, the identification of new probiotics presents a complex challenge, necessitating careful consideration of both the safety and efficacy of the microorganisms employed. This review aims to delineate the most utilized and effective methods for identifying probiotics. The most effective approach currently combines in silico analysis of genomic sequences with in vitro and in vivo experiments. Two main categories of genetic traits are analyzed using bioinformatic tools: those that could harm the host or humans (e.g., toxin production, antibiotic resistance) and those that offer benefits (e.g., production of helpful compounds, and enzymes). Similarly, in vitro experiments allow us to examine the safety of a probiotic but also its effectiveness (e.g., ability to adhere to epithelia). Finally, in vivo experiments allow us to study the effect of probiotics on fish growth and health, including the ability of the probiotic to manipulate the host's microbiota and the ability to mitigate the infections. This review comprehensively analyzes these diverse aspects, with a particular focus on the potential of studying the interaction between bacterial pathogens and probiotics through these integrated methods.

Green synthesis of highly fluorescent carbon quantum dots from almond resin for advanced theranostics in biomedical applications

Fluorescent Carbon Quantum Dots (CQDs) are being used in medical applications, particularly in theranostics. These Carbon Quantum Dots have been gaining more attention lately due to their potential as an effective replacement for hazardous synthetic organic dyes in a variety of biomedical applications, including live cell imaging and diagnostics. In this study, highly fluorescent Carbon Quantum Dots by one pot microwave based green route with a size of less than 10 nm, was prepared from commercially available almond resin, Prunus dulcis and conjugated with honey as additional reagent for surface functionalization. They exhibit a deep blue emission on excitation at 350 nm with an elevated quantum yield at 61%. They possess atomic nature and basic features such as high photo-stability, varying fluorescence, greater biocompatibility, and better water solubility. These fluorescent labels exhibit faster cellular invagination without disturbing the cell stability. The CQDs present cell imaging capacity with multi-coloration for visualizing the fine architecture of the nucleus naming, the nuclear membrane and nucleolus, which is linked with their varied, surface structures such as amphiphilic property and higher positive charges. These characteristics with minimal invasion have made carbon quantum dots to become the spotlight in theranostics. They can be used as alternatives to synthetic dyes for fluorescence- related cell-imaging. The intriguing fact about this approach is that it opens the possibility of combining therapy and diagnostics into one unit, which can alter how some diseases are handled and, in turn, transform the field of healthcare.

Toxic effects of trace metal(loid) mixtures on aquatic organisms

The co-occurrence of metal (loid)s in realistic aquatic environments necessitates the evaluation of their combined effects. However, the generality of the additive effect hypothesis is contentious, particularly due to metal(loid)-metal(loid) interactions. The absence of systematic evaluation approaches restricts our ability to draw overall conclusions and make reliable predictions. In this study, we reviewed 1473 effect sizes from 38 publications, and classified all responses into seven main categories (from molecular to individual levels) according to their toxicological significance. Our meta-analysis revealed that metal(loid) mixtures had significant effects on aquatic organisms (33 %, 95 % CI 28 %-39 %, P < 0.05), along with significant response heterogeneity (Qt = 690,319.62, P < 0.0001; I2 = 99.95 %). Concurrently, we developed a Random Forest machine learning model to predict adverse effects and identify key variables. These two methods demonstrated that the toxicity of metal(loid) mixtures is primarily linked to the choice of toxicity endpoints, and the characteristics of metal(loid) mixtures. Our findings underscore the potential of combining meta-analysis with machine learning, a more systematic approach, to enhance the understanding and prediction of the adverse effects of metal(loid) mixtures, and they offer guidance for risk assessment and policy-making in complex environmental scenarios.

Prediction of acute fish toxicity (AFT) and fish embryo toxicity (FET) tests by cytotoxicity assays using liver and embryo zebrafish cell lines (ZFL and ZEM2S)

Fish cell-based assays represent potential alternative methods to vertebrates' use in ecotoxicology. In this study, we evaluated the cytotoxicity of thirteen chemicals, chosen from OECD guidelines 236 and 249, in two zebrafish cell lines (ZEM2S and ZFL). We aimed to investigate whether the IC50 values obtained by viability assays (alamar blue, MTT, CFDA-AM, and neutral red) can predict the LC50 values of Acute Fish Toxicity (AFT) test and Fish Embryo Toxicity (FET) test. There was no significant difference between the values obtained by the different viability assays. ZFL strongly correlated with AFT and FET tests (R2AFT = 0.73-0.90; R2FET48h = 0.79-0.90; R2FET96h = 0.76-0.87), while ZEM2S correlated better with the FET test (48h) (R2 = 0.70-0.86) and weakly with AFT and FET tests (96h) (R2AFT = 0.68-0.74 and R2FET96h = 0.62-0.64). The predicted LC50 values allowed the correct categorization of the chemicals in 76.9% (AFT test) - 90.9% (FET test) using ZFL and in 30.7% (AFT test) - 63.6% (FET test) using ZEM2S considering the US EPA criterion for classifying acute aquatic toxicity. ZFL is a promising cell line to be used in alternative methods to adult fish and fish embryos in ecotoxicity assessments, and the method performed in 96-well plates is advantageous in promoting high-throughput cytotoxicity assessment.

Immunotoxicity and transcriptome analysis of zebrafish embryos exposure to Nitazoxanide

Nitazoxanide (NTZ) is a broad-spectrum immunomodulatory drug, and little information is about the immunotoxicity of aquatic organisms induced by NTZ. In the present study, reduced body length and decreased yolk sac absorption in the NTZ-treated group were observed. Meanwhile, the number of innate immune cells and adaptive immune cells was substantially reduced upon NTZ exposure, and the migration and retention of macrophages and neutrophils in the injured area were inhibited. Following NTZ stimulation, oxidative stress levels in the zebrafish increased obviously. Mechanistically, RNA-seq, a high-throughput method, was performed to analyze the global expression of differentially expressed genes (DEGs) in zebrafish embryos treated with NTZ. 531 DEGs were identified by comparative transcriptome analysis, including 121 up-regulated and 420 down-regulated genes in zebrafish embryos after NTZ exposure. The transcriptome sequences were further subjected to the Kyoto Encyclopedia of Genes and Genomes (KEGG) and gene ontology (GO) and analysis, showing phototransduction and metabolic pathway, respectively, and were most enriched. In addition, some immune-related genes were inhibited after NTZ exposure. RNA-seq results confirmed by qRT-PCR were used to verify the expression of the 6 selected genes. The other immune-related genes such as two pro-inflammatory cytokines (IL-1β, tnfα) and two chemokines (CXCL8b.3, CXCL-c1c) were further confirmed and were differentially regulated after NTZ exposure. In summary, NTZ exposure could lead to immunotoxicity and increased ROS in zebrafish embryos, this study provides valuable information for future elucidating the molecular mechanism of exogenous stimuli-induced immunotoxicity in aquatic ecosystems.

Biocompatible and Biodegradable Surfactants from Orange Peel for Oil Spill Remediation

Oil spill remediation plays a vital role in mitigating the environmental impacts caused by oil spills. The chemical method is one of the widely recognized approaches in chemical surfactants. However, the most commonly used chemical surfactants are toxic and non-biodegradable. Herein, two biocompatible and biodegradable surfactants were synthesized from orange peel using the ionic liquid 1-butyl-3-methylimidazolium chloride (BMIMCl) and organic solvent dimethylacetamide (CH3CN(CH3)2) as reaction media. The acronyms SOPIL and SOPOS refer to the surfactants prepared with BMIMCl and dimethylacetamide, respectively. The surface tension, dispersant effectiveness, optical microscopy, and emulsion stability test were conducted to examine the comparative performance of the synthesized surfactants. The Baffled flask test (BFT) was carried out to determine the dispersion effectiveness. The toxicity test was performed against zebrafish (Danio rerio), whereas the closed bottle test (CBT) evaluated biodegradability. The results revealed that the critical micelle concentration (CMC) value of SOPIL was lower (8.57 mg/L) than that of SOPOS (9.42 mg/L). The dispersion effectiveness values for SOPIL and SOPOS were 69.78% and 40.30%, respectively. The acute toxicity test demonstrated that SOPIL was 'practically non-toxic' with a median lethal concentration of more than 1000 mg/L after 96 h. The biodegradation rate was recorded as higher than 60% for both surfactants within 28 days, demonstrating their readily biodegradable nature. Considering these attributes, biocompatible and biodegradable surfactants derived from orange peel emerge as a promising and sustainable alternative for oil spill remediation.

Ecotoxicological evaluation of functional carbon nanodots using zebrafish (Danio rerio) model at different developmental stages

Considering functional carbon nanodots (FCNs) are potential to be applied in many areas, their risk and toxicity to organisms are imperative to be evaluated. Thus, this study conducted acute toxicity test of zebrafish (Danio rerio) at embryonic and adult stage to estimate the toxicity of FCNs. Results show that the toxic effects of FCNs and nitrogen doped FCNs (N-FCNs) at their 10% lethal concentration (LC₁₀) values on zebrafish are expressed in developmental retardation, cardiovascular toxicity, renal damage and hepatotoxicity. There are interactive relationships between these effects, but the main reason should be ascribed to the undesirable oxidative damage induced by high doses of materials, as well as the biodistribution of FCNs and N-FCNs in vivo. Even so, FCNs and N-FCNs can promote the antioxidant activity in zebrafish tissues to cope with the oxidative stress. FCNs and N-FCNs are not easy to cross the physical barriers in zebrafish embryos or larvae, and can be excreted from intestine by adult fish, which proves their biosecurity to zebrafish. In addition, because of the differences in physicochemical properties, especially nano-size and surface chemical property, FCNs show higher biosecurity to zebrafish than N-FCNs. The effects of FCNs and N-FCNs on hatching rates, mortality rates and developmental malformations are dose-dependent and time-dependent. The LC₅₀ values of FCNs and N-FCNs on zebrafish embryo at 96 hpf are 1610 mg/L and 649 mg/L, respectively. According to the Acute Toxicity Rating Scale of the Fish and Wildlife Service, the toxicity grades of FCNs and N-FCNs are both defined as "practically nontoxic", and FCNs are "Relatively Harmless" to embryos because their LC₅₀ values are above 1000 mg/L. Our results prove the biosecurity of FCNs-based materials for future practical application.

Effects of Chloramine T on zebrafish embryos malformations associated with cardiotoxicity and neurotoxicity

Chloramine T, a sodium p-toluene sulfonchloramide, is known to possess a wide spectrum of biocidal activity and is employed as a disinfectant in fish farms to treat bacterial infections. Although Chloramine T may effectively combat pathogens, the sublethal and lethal effects and changes in acetylcholinesterase (AChE) activity remain poorly elucidated using Danio rerio (zebrafish) embryos. Zebrafish is considered a model organism for toxicant screening research and exhibits mammalian-like physiological responses when exposed to environmental pollutants. The aim of this study was to (1) determine LC₅₀ of Chloramine T after 96 hr exposure, (2) verify disinfectant effects on developmental morphology, and (3) evaluate the disinfectant effects on AChE activity in zebrafish embryos. Chloramine T exposure was performed using 16, 32, 64, 128, or 256 mg/L concentrations. The mortality LC₅₀ values were 143.05 ± 3.11 and 130.97 ± 7.4 mg/L at 24 and 96 hr, respectively. Data demonstrated delayed hatching, reduced heartbeats, cardiac edema, and equilibrium disruption of hatched larvae throughout embryonic development. In addition, Chloramine T inhibited AChE activity at 64 or 128 mg/L after 96 hr treatment, corroborating the sub-lethality results observed in zebrafish embryo development and demonstrating an equilibrium disruption in zebrafish larvae.

Evaluating the alterations of the estrogen-responsive genes in Cyprinodon variegatus larvae for biomonitoring the impacts of estrogenic endocrine disruptors (EEDs)

Currently, endocrine disruptors (EDs) can be found in all the environmental compartments. To understand the effects of estrogenic EDs (EEDs), adults of Cyprinodon variegatus have been classically used as a marine model. However, it is during development that exposure to contaminants may generate permanent consequences. Thus, the aim of this study was to verify the effects produced by acute exposure to 17α-ethinylestradiol (EE2) in C. variegatus larvae. Quantitative PCR (qPCR) results revealed the induction of vtg and zp gene expression on exposure to 1000 ng/L EE2 and the induction of vtgc, zp2, zp3 and cyp19a2, and inhibition of vtgab, wap and cyp1a1 on exposure to 100 ng/L EE2. Lower concentrations inhibited the gene expression of vtgab and wap (50 ng/L), cyp1a1 (25 ng/L) and zp2 (12.5 ng/L). These alterations in gene expression allow us to affirm that larvae of C. variegatus are an efficient and sensitive model for biomonitoring EEDs.