An Adult Zebrafish Diet Contaminated with Chromium Reduces the Viability of Progeny

Textile azo dye, Sudan Black B, inducing hepatotoxicity demonstrated in in vivo zebrafish larval model

Environmental pollution, particularly from textile industry effluents, raises concerns globally. The aim of this study is to investigate the hepatotoxicity of Sudan Black B (SBB), a commonly used textile azo dye, on embryonic zebrafish. SBB exposure led to concentration-dependent mortality, reaching 100% at 0.8 mM, accompanied by growth retardation and diverse malformations in zebrafish. Biochemical marker analysis indicated adaptive responses to SBB, including increased SOD, CAT, NO, and LDH, alongside decreased GSH levels. Liver morphology analysis unveiled significant alterations, impacting metabolism and detoxification. Also, glucose level was declined and lipid level elevated in SBB-exposed in vivo zebrafish. Inflammatory gene expressions (TNF-α, IL-10, and INOS) showcased a complex regulatory interplay, suggesting an organismal attempt to counteract pro-inflammatory states during SBB exposure. The increased apoptosis revealed a robust hepatic cellular response due to SBB, aligning with observed liver tissue damage and inflammatory events. This multidimensional study highlights the intricate web of responses due to SBB exposure, which is emphasizing the need for comprehensive understanding and targeted mitigation strategies. The findings bear the implications for both aquatic ecosystems and potentially parallels to human health, underscoring the imperative for sustained research in this critical domain.

Zebrafish as model organisms for toxicological evaluations in the field of food science

Food safety has long been an area of concern. The selection of stable and efficient model organisms is particularly important for food toxicology studies. Zebrafish (Danio rerio) are small model vertebrates, and 70% of human genes have at least one zebrafish ortholog. Zebrafish have advantages as model organisms due to their short life cycle, strong reproductive ability, easy rearing, and low cost. Zebrafish embryos have the advantage of being sensitive to the breeding environment and thus have been used as biosensors. Zebrafish and their embryos have been widely used for food toxicology assessments. This review provides a systematic and comprehensive summary of food toxicology studies using zebrafish as model organisms. First, we briefly introduce the multidimensional mechanisms and structure-activity relationship studies of food toxicological assessment. Second, we categorize these studies according to eight types of hazards in foods, including mycotoxins, pesticides, antibiotics, heavy metals, endocrine disruptors, food additives, nanoparticles, and other food-related ingredients. Finally, we list the applications of zebrafish in food toxicology studies in line with future research prospects, aiming to provide a valuable reference for researchers in the field of food science.

Hexavalent Chromium Inhibited Zebrafish Embryo Development by Altering Apoptosis- and Antioxidant-Related Genes

This study aimed to assess the effects of hexavalent chromium on zebrafish (Danio rerio) embryo development. The zebrafish embryos were treated with solutions containing chromium at different concentrations (0.1, 1, 3.125, 6.25, 12.5, 50, and 100 µg/mL). The development of zebrafish embryos was estimated by the determination of survival rate, heart rate, and the measurement of larvae body length. Real time RT-PCR and Western blot were performed to assess the expression of apoptosis- and antioxidant-related genes. The results showed that the reduced survival rate of zebrafish embryos and larvae was associated with an increase in chromium concentration. The exposure of higher concentrations resulted in a decrease in body length of zebrafish larvae. In addition, a marked increase in heart rate was observed in the zebrafish larvae under chromium treatment, especially at high concentrations. The real-time RT-PCR analysis showed that the transcript expressions for cell-cycle-related genes (cdk4 and cdk6) and antioxidant-related genes (sod1 and sod2) were downregulated in the zebrafish embryos treated with chromium. Western blot analysis revealed the upregulation of Caspase 3 and Bax, while a downregulation was observed in Bcl2. These results indicated that hexavalent chromium induced changes in zebrafish embryo development by altering apoptosis- and antioxidant-related genes.

Investigation of Different Nutritional Effects of Dietary Chromium in Fish: A Literature Review

The supply of food for the world population that is increasing is one of the concerns of governments. The Food and Agriculture Organization of the United Nations assessment shows that the aquaculture industry could help meet food needs for human communities. The aquaculture industry also relies on providing a feed of high quality. Minerals are one essential component of an aquatic diet. Chromium (Cr) is a trace element that finds the form of Cr⁺³ (trivalent) and Cr⁺⁶ (hexavalent) in nature and food items. Studies show that exposure to Cr waterborne have toxicity effects on fish. However, oral exposure to Cr has a different impact on fish. Cr is usually involved in the metabolism of fats, carbohydrates, proteins, growth function, enzyme functions, etc. This element could play a significant role in fish nutrition and physiology. Cr as a dietary supplement can improve growth performance and adjust the metabolism of carbohydrates and lipids. However, high concentrations of Cr can be toxic to fish. Although the physiological effects of Cr on aquatic organisms are well known, there are still ambiguities in determining the appropriate concentration in the diet of some species. Maybe, the physiological response of fish depends on the concentration, origin, and chemical composition of Cr, as well as the biological and individual characteristics of the fish. Therefore, it is necessary to estimate the appropriate concentration of Cr in fish diets. This article aims to summarize the available information about the effect of Cr on various physiological indicators and fish growth. Therefore, this information may help to find the appropriate concentration of Cr in the diet.

Background per- and polyfluoroalkyl substances (PFAS) in laboratory fish diet: Implications for zebrafish toxicological studies

Current attention is focused on determining the potential for per- and polyfluoroalkyl substances (PFAS) to adversely impact human health. Zebrafish are a popular biological model because they share early development pathways with humans. A dietary exposure paradigm is growing in popularity in the zebrafish model because the outcomes often translate to humans. To create a diet of known composition, it is crucial to understand background PFAS levels present in zebrafish diet. Background PFAS, if present, potentially confounds interpretation of toxicological data. To date, no studies document the PFAS background levels in laboratory fish diet and there is only limited information on some pet foods. The objective of this study was to develop and validate an analytical method for up to 50 target PFAS in high lipid and protein content laboratory fish diets and pet foods. Long-chain perfluoroalkyl carboxylic acids (C9-C13) and perfluorooctane sulfonate (PFOS) were quantified in 11 out of 16 laboratory fish diets and in three out of five pet fish foods. Foods for pet birds, lizards, and dogs were below the limit of detection for all PFAS. In two of the laboratory fish diets, PFOS concentrations were >1.3 ng/g and the total PFAS for the three laboratory fish diets exceeded 1.0 ng/g. Hundreds of biomedical laboratories across the world utilize these commercial laboratory fish diets, and these results indicate that numerous zebrafish colonies may be inadvertently receiving significant dietary PFAS exposures. In light of this new information, it is critical to design PFAS studies with appropriate controls with measured background PFAS concentrations in the diet and to urge caution when interpreting the results.

Generation of a novel transgenic marine medaka (Oryzias melastigma) for highly sensitive detection of heavy metals in the environment

As typic priority pollutants in the marine environment, heavy metals can be accumulated in the human body leading to serious environmental and health problems. The metal regulatory elements (MREs) have been identified to be the main functional parts for the response to heavy metals. To develop a convenient biological monitoring tool for the detection of heavy metals in the oceans, we generated a transgenic marine medaka line Tg(OmMT: eGFP) with a truncated metallothionein promoter, which was only 193 bp and drove the expression of eGFP. After Tg(OmMT:eGFP) embryos were treated with four different heavy metals and different concentrations, the results showed that the expression level of eGFP was consistent with that of the endogenous mt. The transgenic embryos are very sensitive to Hg²⁺, and the fluorescence could be induced in the 0.0002 μM concentration, which is far lower than the primary water standard. The expression level of eGFP and mt showed a dose-dependent manner to heavy metals concentration. Taken together, the newly established marine medaka is a sensitive, efficient, and convenient tool for monitoring heavy metal pollution in the environment, especially seawater.

A Systematic Analysis of Metal and Metalloid Concentrations in Eight Zebrafish Recirculating Water Systems

Metals and metalloids are integral to biological processes and play key roles in physiology and metabolism. Nonetheless, overexposure to some metals or lack of others can lead to serious health consequences. In this study, eight zebrafish facilities collaborated to generate a multielement analysis of their centralized recirculating water systems. We report a first set of average concentrations for 46 elements detected in zebrafish facilities. Our results help to establish an initial baseline for trouble-shooting purposes, and in general for safe ranges of metal concentrations in recirculating water systems, supporting reproducible scientific research outcomes with zebrafish.

Comparison of Juvenile Feed Protocols on Growth and Spawning in Zebrafish

Over the past 2 decades, zebrafish, Danio rerio, have become a mainstream laboratory animal model, yet zebrafish husbandry practices remain far from standardized. Feeding protocols play a critical role in the health, wellbeing, and productivity of zebrafish laboratories, yet they vary significantly between facilities. In this study, we compared our current feeding protocol for juvenile zebrafish (30 dpf to 75 dpf), a 3:1mixture of fish flake and freeze-dried krill fed twice per day with live artemia twice per day (FKA), to a diet of Gemma Micro 300 fed once per day with live artemia once per day (GMA). Our results showed that juvenile EK wild-type zebrafish fed GMA were longer and heavier than juveniles fed FKA. As compared with FKA-fed juveniles, fish fed GMA as juveniles showed better reproductive performance as measured by spawning success, fertilization rate, and clutch size. As adults, fish from both feeding protocols were acclimated to our standard adult feeding protocol, and the long-term effects of juvenile diet were assessed. At 2 y of age, the groups showed no difference in mortality or fecundity. Reproductive performance is a crucial aspect of zebrafish research, as much of the research focuses on the developing embryo. Here we show that switching juvenile zebrafish from a mixture of flake and krill to Gemma Micro 300 improves reproductive performance, even with fewer feedings of live artemia, thus simplifying husbandry practices.

Transgenerational Effects of Hexavalent Chromium on Marine Medaka (Oryzias melastigma) Reveal Complex Transgenerational Adaptation in Offspring

Hexavalent chromium [Cr(VI)] pollution is one of most serious heavy metal pollutants in the coastal area and posed serious threats to marine organisms and human beings. Many studies have been conducted on its toxicological effects on living organisms from morphological to physiological aspects. However, there are few studies about the transgenerational toxicological of Cr(VI). In this study, we exposed adult marine medaka fishes with Cr(VI) and their offspring with Cr(VI) to examine transgenerational effects of Cr(VI). We found that there were mechanisms such as changing reproduction modes in males to compensate for impacts on the reproduction. There were differences and similarities between the parental effect and the environmental effect, with the former one causing more serious adverse effects on the offspring of Cr(VI)-exposed fish. It was noteworthy that there was an interaction between the parental and offspring treatment which leads to the attenuation of the parental effects on offspring when the offspring also underwent the same treatment. In addition, physiological adaptation has also been observed in fish to improve their fitness. Overall, effects of Cr(VI) on fish and their offspring were studied to pave a way to study the of mechanisms of adaptation.

The Role of Feed in Aquatic Laboratory Animal Nutrition and the Potential Impact on Animal Models and Study Reproducibility

Feed plays a central role in the physiological development of terrestrial and aquatic animals. Historically, the feeding practice of aquatic research species derived from aquaculture, farmed, or ornamental trades. These diets are highly variable, with limited quality control, and have been typically selected to provide the fastest growth or highest fecundity. These variations of quality and composition of diets may affect animal/colony health and can introduce confounding experimental variables into animal-based studies that impact research reproducibility.

Ecological risks of heavy metals/metalloid discharged from two sewage treatment works to Mai Po Ramsar site, South China

The concentrations of six heavy metal/metalloids (HMs) cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), zinc (Zn), and arsenic (As) were determined in the influent, effluent, and dewatered sludge of two sewage treatment works (Yuen Long Sewage Treatment Work (YLSTW) and Shek Wu Hui Sewage Treatment Work (SWHSTW)) and river waters and sediment (Shan Pui River and Ng Tung River) within the Mai Po Ramsar site in Hong Kong SAR, China. In both STWs, Pb had the highest removal efficiencies (YLSTW 86.5 ± 19.0% to 97.3 ± 3.04%; SWHSTW 87.4 ± 12.8% to 100 ± 0.0800%). In the whole effluent toxicity test, both STWs were effective in lowering the toxicity of the effluent to zebrafish and cherry shrimp. The environmental risk assessments of these HMs on three local aquatic organisms, three species of fish, two species of crustaceans, and three species of algae, were calculated based on measured HMs concentrations in river water and sewage samples, and the predicted no-effect concentrations. Results showed that Zn concentrations in all collected samples posed potential risks to all studied aquatic organisms (average risk quotient = 445). The concentrations of Cu in the rivers posed potential risks (average risk quotient = 5.42) to all fish species. It was concluded that Zn and Hg derived from the STWs might pose potential risks to the living organisms inhabiting the Ramsar site, and Cu, Cd, Pb, and As in the rivers were originated from the two rivers and possibly other tributaries.

Dietary Contaminants and Their Effects on Zebrafish Embryos

Dietary contaminants are often an over-looked factor in the health of zebrafish. Typically, water is considered to be the source for most contaminants, especially within an aquatic environment. For this reason, source water for zebrafish recirculating systems is highly regulated and monitored daily. Most facilities use reverse osmosis or de-ionized water filtration systems to purify incoming water to ensure that contaminants, as well as pathogens, do not enter their zebrafish housing units. However, diets are rarely tested for contaminants and, in the case of manufactured zebrafish feeds, since the product is marketed for aquaculture or aquarium use it is assumed that the feed is acceptable for animals used for research. The following provides examples as to how contaminants could lead to negative effects on development and behavior of developing zebrafish.