Fundamental approaches to the study of zebrafish nutrition

Evaluation of a gel-based versus micro-pellet diet for adult zebrafish (Danio rerio)

Ad libitum feeding of laboratory zebrafish has potential benefits for colony management, but would require a new type of diet, such as a gel that remains in the tank. We hypothesized that adult zebrafish fed a gel diet would have similar body size and reproductive success compared with those fed a standard micro-pellet diet. The gel diet’s impact on water quality was determined to be safe for zebrafish prior to starting a 12-week feeding study. Two hundred adult AB zebrafish of mixed sex were randomly assigned to be fed exclusively either gel or micro-pellet diet. Fish body length and mass were measured every two weeks, and fish were bred within each feed group to assess fecundity. Zebrafish consumed less gel diet than expected. Body length, mass, and breeding success were lower in the gel diet fish than in the micro-pellet diet fish. Low consumption of the gel diet and/or nutritional differences between the two diets may have contributed to reduced growth and fecundity. Though the gel diet could reduce time personnel spend feeding and be safer for fish in static tanks, the tested formulation was not a satisfactory alternative to the control micro-pellet diet in a research zebrafish colony.

Considerations for protein and amino acids in standardized reference diet for parthenogenetic marbled crayfish Procambarus virginalis model organism

The concept of a standardized reference diet (SRD) is used in laboratory model organisms to ensure nutritional control between studies and laboratories. Although models using the genetically identical, all female parthenogenetic marbled crayfish (Procambarus virginalis) are growing in popularity, research into nutrition in this species still has many knowledge gaps. To fast track the development of a SRD in terms of protein and amino acids (SRDprotein) for this species, we first analyzed the composition of its body amino acids to determine the ideal protein concept (IPC) of indispensable amino acids in wild-caught P. virginalis (which had an unusually high preponderance of leucine and arginine). Then, we strategically evaluated three common clusters of types of fish feed: (1) ornamental fish feed (SER) fortified with a naturally occurring alga (Spirulina). This type of feed was protein-high in arginine and leucine (SER + SPI) that fulfils the species' IPC for iso-protein (~ 40%), iso-phosphorus (~ 0.8%) and near iso-energetic (~ 475 kcal 100 g-1); (2) freeze-dried live feed consisting of chironomid larvae (CHI) fortified with Spirulina (CHI + SPI) that fulfils the IPC for iso-protein (~ 46%), iso-phosphorus (~ 0.7%) and near iso-energetic (~ 405 kcal 100 g-1); and (3) a commercially standardized 'starter diet' for carnivorous fish larvae (FISH) and post-larval shrimps (SHRIMP) with iso-protein (~ 56%) and iso-phosphorus (~ 1.6%). A total of six diets, embracing a diverse range of proteinaceous feeds, were used in a 100-day ad libitum feeding and growth trial. The FISH group outperformed all the other groups (p < 0.05) and our exploratory multivariate analysis revealed an ideal demand of > 44% protein (tailored to deliver high arginine 3% and leucine 4%, followed by the usual lysine > 3.5% and methionine 1.2%) but also the lowest carbohydrate level (21%). For SRDprotein, our findings show that the FISH diet is ideal and suggest the possibilities of using a CHI + SPI diet for further optimization (more economic use of protein and phosphorus).

Considerations for fatty acids in standardized reference diet for parthenogenetic marbled crayfish Procambarus virginalis model organism

Fatty acid accumulation was studied in the parthenogenetic all-female marbled crayfish Procambarus virginalis using six arbitrarily designed experimental feeds and related to individuals with glair glands (sexual maturity) after 100 days of ad libitum feeding at 21 °C, including gravid females from the wild as a reference. Fatty acids 16:0 and 18:1n-9 comprised 40% of the total amount of fatty acids and tended to up-concentrate in bodies. Shorter chain 14:0 depleted from feed to body. Across diets, there was a concomitant decrease in precursor fatty acid and increase in product fatty acid, such as reinforcements in monounsaturated fatty acid (18:1n-9), eicosanoid precursors 20:4n-6 (arachidonic acid, ARA) and 20:5n-3 (eicosapentaenoic acid, EPA) in-vivo, but not 22:6n-3 (docosahexaenoic acid, DHA) except when deficient in CHI or CHI + SPI diets. Saturation kinetics modeling (R2 0.7-0.9, p < 0.05) showed that when the ARA share is ~ 1%, the EPA share is ~ 8%, and the DHA share is ~ 2% in the food lipids, the accumulation of fatty acids in body lipids levels off. The lowest DHA in the CHI (0% glair glands) or CHI + SPI (0-3.9% glair glands) diets, and the lowest ARA in SER (0% glair glands) or SER + SPI (0-3% glair glands) diets, were synchronous with negligible sexual maturity despite a wide range of observed specific growth rates (2.77-3.60% per day), body size (0.44-0.84 g), ≤ 5% crude lipid and 40-46% crude protein feed. The FISH and SHRIMP diets (56% protein, 11-14% lipid) with the highest ARA, EPA, and DHA together seem to be the most conducive diets for sexual maturity (up to 20% of individuals with glair glands). We propose a fatty acid profile mimicking the FISH or SHRIMP diets as a starting point for designing the lipid content required in the marbled crayfish standardized reference diet.

Chronotropic and vasoactive properties of the gut bacterial short-chain fatty acids in larval zebrafish

Short-chain fatty acids (SCFAs) produced by the gut bacteria have been associated with cardiovascular dysfunction in humans and rodents. However, studies exploring effects of SCFAs on cardiovascular parameters in the zebrafish, an increasingly popular model in cardiovascular research, remain limited. Here, we performed fecal bacterial 16S sequencing and gas chromatography/mass spectrometry (GC-MS) to determine the composition and abundance of gut microbiota and SCFAs in adult zebrafish. Following this, the acute effects of major SCFAs on heart rate and vascular tone were measured in anesthetized zebrafish larvae using fecal concentrations of butyrate, acetate, and propionate. Finally, we investigated if coincubation with butyrate may lessen the effects of angiotensin II (ANG II) and phenylephrine (PE) on vascular tone in anesthetized zebrafish larvae. We found that the abundance in Proteobacteria, Firmicutes, and Fusobacteria phyla in the adult zebrafish resembled those reported in rodents and humans. SCFA levels with highest concentration of acetate (27.43 µM), followed by butyrate (2.19 µM) and propionate (1.65 µM) were observed in the fecal samples of adult zebrafish. Immersion in butyrate and acetate produced a ∼20% decrease in heart rate (HR), respectively, with no observed effects of propionate. Butyrate alone also produced an ∼25% decrease in the cross-sectional width of the dorsal aorta (DA) at 60 min (*P < 0.05), suggesting compensatory vasoconstriction, with no effects of either acetate or propionate. In addition, butyrate significantly alleviated the decrease in DA cross-sectional width produced by both ANG II and PE. We demonstrate the potential for zebrafish in investigation of host-microbiota interactions in cardiovascular health.NEW & NOTEWORTHY We highlight the presence of a core gut microbiota and demonstrate in vivo short-chain fatty acid production in adult zebrafish. In addition, we show cardio-beneficial vasoactive and chronotropic properties of butyrate, and chronotropic properties of acetate in anesthetized zebrafish larvae.

Chronic Behavioral and Neurochemical Effects of Four Novel N-Benzyl-2-phenylethylamine Derivatives Recently Identified as "Psychoactive" in Adult Zebrafish Screens

Potently affecting human and animal brain and behavior, hallucinogenic drugs have recently emerged as potentially promising agents in psychopharmacotherapy. Complementing laboratory rodents, the zebrafish (Danio rerio) is a powerful model organism for screening neuroactive drugs, including hallucinogens. Here, we tested four novel N-benzyl-2-phenylethylamine (NBPEA) derivatives with 2,4- and 3,4-dimethoxy substitutions in the phenethylamine moiety and the -F, -Cl, and -OCF3 substitutions in the ortho position of the phenyl ring of the N-benzyl moiety (34H-NBF, 34H-NBCl, 24H-NBOMe(F), and 34H-NBOMe(F)), assessing their behavioral and neurochemical effects following chronic 14 day treatment in adult zebrafish. While the novel tank test behavioral data indicate anxiolytic-like effects of 24H-NBOMe(F) and 34H-NBOMe(F), neurochemical analyses reveal reduced brain norepinephrine by all four drugs, and (except 34H-NBCl) - reduced dopamine and serotonin levels. We also found reduced turnover rates for all three brain monoamines but unaltered levels of their respective metabolites. Collectively, these findings further our understanding of complex central behavioral and neurochemical effects of chronically administered novel NBPEAs and highlight the potential of zebrafish as a model for preclinical screening of small psychoactive molecules.

Development of a zebrafish model for toxicity evaluation of adulterated Apis mellifera honey

Since ancient times, honey has been used for medical purposes and the treatment of various disorders. As a high-quality food product, the honey industry is prone to fraud and adulteration. Moreover, limited experimental studies have investigated the impact of adulterated honey consumption using zebrafish as the animal model. The aims of this study were: (1) to calculate the lethal concentration (LC50) of acid-adulterated Apis mellifera honey on embryos, (2) to investigate the effect of pure and acid-adulterated A. mellifera honey on hatching rate (%) and heart rate of zebrafish (embryos and larvae), (3) to elucidate toxicology of selected adulterated honey based on lethal dose (LD50) using adult zebrafish and (4) to screen the metabolites profile of adulterated honey from blood serum of adult zebrafish. The result indicated the LC50 of 31.10 ± 1.63 (mg/ml) for pure A. mellifera honey, while acetic acid demonstrates the lowest LC50 (4.98 ± 0.06 mg/ml) among acid adulterants with the highest mortality rate at 96 hpf. The treatment of zebrafish embryos with adulterated A. mellifera honey significantly (p ≤ 0.05) increased the hatching rate (%) and decreased the heartbeat rate. Acute, prolong-acute, and sub-acute toxicology tests on adult zebrafish were conducted at a concentration of 7% w/w of acid adulterants. Furthermore, the blood serum metabolite profile of adulterated-honey-treated zebrafish was screened by LC-MS/MS analysis and three endogenous metabolites have been revealed: (1) Xanthotoxol or 8-Hydroxypsoralen, (2) 16-Oxoandrostenediol, and (3) 3,5-Dicaffeoyl-4-succinoylquinic acid. These results prove that employed honey adulterants cause mortality that contributes to higher toxicity. Moreover, this study introduces the zebrafish toxicity test as a new promising standard technique for the potential toxicity assessment of acid-adulterated honey in this study and hazardous food adulterants for future studies.

Zebrafish Feed Intake: A Systematic Review for Standardizing Feeding Management in Laboratory Conditions

Zebrafish are one of the most used animal models in biological research and a cost-effective alternative to rodents. Despite this, nutritional requirements and standardized feeding protocols have not yet been established for this species. This is important to avoid nutritional effects on experimental outcomes, and especially when zebrafish models are used in preclinical studies, as many diseases have nutritional confounding factors. A key aspect of zebrafish nutrition is related to feed intake, the amount of feed ingested by each fish daily. With the goal of standardizing feeding protocols among the zebrafish community, this paper systematically reviews the available data from 73 studies on zebrafish feed intake, feeding regimes (levels), and diet composition. Great variability was observed regarding diet composition, especially regarding crude protein (mean 44.98 ± 9.87%) and lipid content (9.91 ± 5.40%). Interestingly, the gross energy levels of the zebrafish diets were similar across the reviewed studies (20.39 ± 2.10 kilojoules/g of feed). In most of the reviewed papers, fish received a predetermined quantity of feed (feed supplied). The authors fed the fish according to the voluntary intake and then calculated feed intake (FI) in only 17 papers. From a quantitative point of view, FI was higher than when a fixed quantity (pre-defined) of feed was supplied. Also, the literature showed that many biotic and abiotic factors may affect zebrafish FI. Finally, based on the FI data gathered from the literature, a new feeding protocol is proposed. In summary, a daily feeding rate of 9-10% of body weight is proposed for larvae, whereas these values are equal to 6-8% for juveniles and 5% for adults when a dry feed with a proper protein and energy content is used.

A new approach to explore the correlation between declarative memory and anxiety in animal models of schizophrenia and microplastic pollution

The discovery of new detrimental effects associated with microplastic pollution is ever-growing and reaching alarming rates worldwide, as it is linked to numerous disorders such as lung diseases, gastrointestinal problems, and cancer. However, a less explored issue is their impact on mental health, more precisely schizophrenia, even though several studies have shown the presence of microplastics in air, water, soil, and even food, thus making them a significant part of our daily dietary intake. It is also well known that declarative memory and anxiety levels are impaired in schizophrenia. However, apart from the novel object recognition test, the possibilities for testing memory in zebrafish are quite limited. For these reasons, we designed a novel memory test based on rewards, a learning period, and zebrafish's natural preference for certain colors. Among the results, our fish preferred the color yellow over red, and we illustrated that ketamine and its combination with methionine provide a robust model that seems to better represent the aspects of schizophrenia in animal models. Moreover, surprisingly, we observed that microplastics (more precisely, polypropylene fibers) ingested by animals through the diet seem to act as a buffer against ketamine toxicity and as an enhancer for methionine exposure. Moreover, according to our results, groups with higher anxiety levels seem to perform better on the memory test.

Innovative high fat diet establishes a novel zebrafish model for the study of visceral obesity

Obesity is a complex chronic condition associated with multiple health risks, including visceral obesity, which is particularly detrimental. To gain insight into the mechanisms underlying obesity and its associated pathologies, a novel zebrafish model was established using an innovative high-fat diet (HFD). The primary goal was to induce visceral obesity in zebrafish and study the associated structural changes. To achieve this, a unique HFD consisting of 40% beef fat (HFD40) was developed and supplemented with magnesium aluminometasilicate to improve stability in a high humidity environment. Feeding regimens were initiated for both juvenile (starting at 2 weeks post-fertilization, lasting 18 weeks) and adult zebrafish (3 months post-fertilization, 8 weeks feeding duration). The innovative dietary approach successfully induced visceral obesity in both juvenile and adult zebrafish. This new model provides a valuable tool to study obesity-related pathologies, metabolic syndrome, and potential therapeutic interventions. Most importantly, the low-cost and easy-to-prepare composition of HFD40 was seamlessly incorporated into the water without the need for separation, was readily absorbed by the fish and induced rapid weight gain in the zebrafish population. In conclusion, this study presents a novel HFD40 composition enriched with a high beef fat concentration (40%), which represents a significant advance in the development of an experimental zebrafish model for the study of visceral obesity and associated metabolic changes.

A Bacterial-Sourced Protein Diet Induces Beneficial Shifts in the Gut Microbiome of the Zebrafish, Danio rerio

Background

Bacterial-sourced single-cell proteins (SCPs) offer an alternative protein source for diet formulation for Zebrafish (Danio rerio) and other aquaculture models. In addition, the use of a single-cell bacterial protein source derived from multiple species provides a unique insight into the interplay among nutrients in the diet, microbial populations in the diet, and the gut microbiome in D. rerio.

Objective

Our objective in this study was to evaluate the impact of dietary replacement of fish protein hydrolysate in a standard reference (SR) with a single-cell bacterial protein source on D. rerio gut microbiome.

Methods

We investigated gut microbial compositions of D. rerio fed an open-formulation standard reference (SR) diet or a bacterial-sourced protein (BP) diet, utilizing microbial taxonomic co-occurrence networks, and predicted functional profiles.

Results

Microbial communities in the SR diet were primarily composed of Firmicutes. In contrast, the BP diet was mainly composed of Proteobacteria. Alpha diversity revealed significant differences in microbial communities between the 2 diets, and between the guts of D. rerio fed either of the 2 diets. D. rerio fed with the SR diet resulted in abundance of Aeromonas and Vibrio. In contrast, D. rerio fed with a BP diet displayed a large abundance of members from the Rhodobacteraceae family. Taxonomic co-occurrence networks display unique microbial interactions, and key taxons in D. rerio gut samples were dependent on diet and gender. Predicted functional profiling of the microbiome across D. rerio fed SR or BP diets revealed distinct metabolic pathway differences. Female D. rerio fed the BP diet displayed significant upregulation of pathways related to primary and secondary bile acid synthesis. Male D. rerio fed the BP diet revealed similar pathway shifts and, additionally, a significant upregulation of the polyketide sugar unit biosynthesis pathway.

Conclusions

The use of a BP dramatically affects the composition and activity of the gut microbiome. Future investigations should further address the interplay among biological systems and diet and may offer insights into potential health benefits in preclinical and translational animal models.

Beyond compliance: harmonising research and husbandry practices to improve experimental reproducibility using fish models

Reproducibility in animal research is impacted by the environment, by husbandry practices in the laboratory and by the animals' provenance. These factors, however, are often not adequately considered by researchers. A disconnect between researchers and animal care staff can result in inappropriate housing and husbandry decisions for scientific studies with those animals. This is especially the case for the research in neuro-behaviour, epigenetics, and the impact of climate change, as heritable phenotypic, behavioural or physiological changes are known to result from the animals' environmental housing, husbandry, provenance and prior experience. This can lead to greater variation (even major differences) in data outcomes among studies, driving scientific uncertainties. Herein, we illustrate some of the endpoints measured in fish studies known to be intrinsically linked to the environment and husbandry conditions and assess the significance of housing and husbandry practice decisions for research adopting these endpoints for different fish species. We highlight the different priorities and challenges faced by researchers and animal care staff and how harmonising their activities and building greater understanding of how husbandry practices affect the fish will improve reproducibility in research outcomes. We furthermore illustrate how improving engagement between stakeholders, including regulatory bodies, can better underpin fish husbandry decisions and where researchers could help to drive best husbandry practices through their own research with fish models.

Systematic analysis of proximal midgut- and anorectal-originating contractions in larval zebrafish using event feature detection and supervised machine learning algorithms

BACKGROUND

Zebrafish larvae are translucent, allowing in vivo analysis of gut development and physiology, including gut motility. While recent progress has been made in measuring gut motility in larvae, challenges remain which can influence results, such as how data are interpreted, opportunities for technical user error, and inconsistencies in methods.

METHODS

To overcome these challenges, we noninvasively introduced Nile Red fluorescent dye to fill the intraluminal gut space in zebrafish larvae and collected serial confocal microscopic images of gut fluorescence. We automated the detection of fluorescent-contrasted contraction events against the median-subtracted signal and compared it to manually annotated gut contraction events across anatomically defined gut regions. Supervised machine learning (multiple logistic regression) was then used to discriminate between true contraction events and noise. To demonstrate, we analyzed motility in larvae under control and reserpine-treated conditions. We also used automated event detection analysis to compare unfed and fed larvae.

KEY RESULTS

Automated analysis retained event features for proximal midgut-originating retrograde and anterograde contractions and anorectal-originating retrograde contractions. While manual annotation showed reserpine disrupted gut motility, machine learning only achieved equivalent contraction discrimination in controls and failed to accurately identify contractions after reserpine due to insufficient intraluminal fluorescence. Automated analysis also showed feeding had no effect on the frequency of anorectal-originating contractions.

CONCLUSIONS & INFERENCES

Automated event detection analysis rapidly and accurately annotated contraction events, including the previously neglected phenomenon of anorectal contractions. However, challenges remain to discriminate contraction events based on intraluminal fluorescence under treatment conditions that disrupt functional motility.

Dietary exposure to the food preservative tert-Butylhydroquinone (tBHQ) impairs zebrafish (Danio rerio) survival, growth, organ development, and gene expression in Nrf2a-dependent and independent ways

Tert-Butylhydroquinone (tBHQ), a preservative used to prevent oxidative deterioration of oil, fat, and meat products, has been linked to both chemoprotective and adverse effects. This study investigates the impact of dietary tBHQ consumption on survival, growth parameters, organ development, and gene expression in zebrafish (Danio rerio). As tBHQ activates the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2a), a zebrafish line with a mutation in the DNA-binding domain of Nrf2a was used to identify Nrf2a-dependent vs independent effects. Homozygous Nrf2a wildtype (wt) and mutant (m) larvae were fed a diet containing 5% tBHQ or a control diet. Survival and growth parameters were assessed at 15 days and at 5 months, and samples were collected for RNA sequencing at 5 months. Dietary exposure to tBHQ throughout the larval and juvenile periods negatively impacted growth and survival. RNA-seq analysis found differentially expressed genes related to growth and development and upregulation of several immune system-related pathways. The findings herein demonstrate that dietary tBHQ exposure may impair growth and survival in both Nrf2a dependent and independent manners.

Body Metrics and the Gut Microbiome in Response to Macronutrient Limitation in the Zebrafish Danio rerio

Background

Healthy and predictable physiologic homeostasis is paramount in animal models for biomedical research. Proper macronutrient intake is an essential and controllable environmental factor for maintaining animal health and promoting experimental reproducibility.

Objective and Methods

Evaluate reductions in dietary macronutrient composition on body weight metrics, composition, and gut microbiome in Danio rerio.

Methods

D. rerio were fed reference diets deficient in either protein or lipid content for 14 weeks.

Results

Diets of reduced-protein or reduced-fat resulted in lower weight gain than the standard reference diet in male and female D. rerio. Females fed the reduced-protein diet had increased total body lipid, suggesting increased adiposity compared with females fed the standard reference diet. In contrast, females fed the reduced-fat diet had decreased total body lipid compared with females fed the standard reference diet. The microbial community in male and female D. rerio fed the standard reference diet displayed high abundances of Aeromonas, Rhodobacteraceae, and Vibrio. In contrast, Vibrio spp. were dominant in male and female D. rerio fed a reduced-protein diet, whereas Pseudomonas displayed heightened abundance when fed the reduced-fat diet. Predicted functional metagenomics of microbial communities (PICRUSt2) revealed a 3- to 4-fold increase in the KEGG (Kyoto Encyclopedia of Genes and Genomes) functional category of steroid hormone biosynthesis in both male and female D. rerio fed a reduced-protein diet. In contrast, an upregulation of secondary bile acid biosynthesis and synthesis and degradation of ketone bodies was concomitant with a downregulation in steroid hormone biosynthesis in females fed a reduced-fat diet.

Conclusions

These study outcomes provide insight into future investigations to understand nutrient requirements to optimize growth, reproductive, and health demographics to microbial populations and metabolism in the D. rerio gut ecosystem. These evaluations are critical in understanding the maintenance of steady-state physiologic and metabolic homeostasis in D. rerio. Curr Dev Nutr 20xx;x:xx.

Methodological advancements in organ-specific ectopic lipid quantitative characterization: Effects of high fat diet on muscle and liver intracellular lipids

OBJECTIVE

Ectopic lipid accumulation is a hallmark of metabolic diseases, linking obesity to non-alcoholic fatty liver disease, insulin resistance and diabetes. The use of zebrafish as a model of obesity and diabetes is raising due to the conserved properties of fat metabolism between humans and zebrafish, the homologous genes regulating lipid uptake and transport, the implementation of the '3R's principle and their cost-effectiveness. To date, a method allowing the conservation of lipid droplets (LDs) and organs in zebrafish larvae to image ectopic lipids is not available. Our objectives were to develop a novel methodology to quantitatively evaluate organ-specific LDs, in skeletal muscle and liver, in response to a nutritional perturbation.

METHODS

We developed a novel embedding and cryosectioning protocol allowing the conservation of LDs and organs in zebrafish larvae. To establish the quantitative measures, we used a three-arm parallel nutritional intervention design. Zebrafish larvae were fed a control diet containing 14% of nutritional fat or two high fat diets (HFDs) containing 25 and 36% of dietary fats. In muscle and liver, LDs were characterized using immunofluorescence confocal microscopy. In liver, intrahepatocellular lipids were discriminated from intrasinusoid lipids. To complete liver characteristics, fibrosis was identified with Masson's Trichrome staining. Finally, to confirm the conservation and effect of HFD, molecular players of fat metabolism were evaluated by RT-qPCR.

RESULTS

The cryosections obtained after setting up the embedding and cryopreservation method were of high quality, preserving tissue morphology and allowing the visualization of ectopic lipids. Both HFDs were obesogenic, without modifying larvae survival or development. Neutral lipid content increased with time and augmented dietary fat. Intramuscular LD volume density increased and was explained by an increase in LDs size but not in numbers. Intrahepatocellular LD volume density increased and was explained by an increased number of LDs, not by their increased size. Sinusoid area and lipid content were both increased. Hepatic fibrosis appeared with both HFDs. We observed alterations in the expression of genes associated with LD coating proteins, LD dynamics, lipogenesis, lipolysis and fatty acid oxidation.

CONCLUSIONS

In this study, we propose a reproducible and fast method to image zebrafish larvae without losing LD quality and organ morphology. We demonstrate the impact of HFD on LD characteristics in liver and skeletal muscle accompanied by alterations of key players of fat metabolism. Our observations confirm the evolutionarily conserved mechanisms in lipid metabolism and reveal organ specific adaptations. The methodological advancements proposed in this work open the doors to study organelle adaptations in obesity and diabetes related research such as lipotoxicity, organelle contacts and specific lipid depositions.

Dietary Supplementation with a Blend of Hydrolyzable and Condensed Tannins Ameliorates Diet-Induced Intestinal Inflammation in Zebrafish (Danio rerio)

The current study evaluated the effects of hydrolyzable and condensed tannins from chestnut and quebracho wood, respectively (TSP, Silvafeed^®), on zebrafish with intestinal inflammation induced by a plant-based diet (basal diet). Four experimental diets were prepared as follows: the basal diet + 0 TSP, the basal diet + TSP at 0.9 g/kg of feed, the basal diet + TSP at 1.7 g/kg of feed, and the basal diet + TSP at 3.4 g/kg of feed. Eighty-four zebrafish (Danio rerio) were fed for 12 days with the experimental diets. In zebrafish fed the basal diet, intestine integrity appeared to be altered, with damaged intestinal villi, high immunoexpression of tumor necrosis factor-α (TNFα) and cyclooxygenase 2 (COX2), and high expression of the cox2, interleukin 1 (il-1b), interleukin 8 (cxcl8-l1), and tnfα genes. The tannin treatment partially restored intestinal morphology and downregulated the expression of cytokines. The best activity was detected with 1.7 and 3.4 g/kg of feed. In the guts of all groups, Proteobacteria, Fusobacteria, Firmicutes, and Bacteroidetes were the most represented phyla. The most represented genera were Plesiomonas and Sphingomonas, belonging to the Proteobacteria phylum; Cetobacterium, belonging to the Fusobacteria phylum; and Lactobacillus, belonging to the Firmicutes phylum. No significant differences were detected among groups, except for a slight decrease in the Fusobacteria phylum and slight increases in the Shewanella and Bacteroides genera with TSP. In conclusion, these results suggest that tannins can improve the zebrafish intestinal inflammation caused by a terrestrial-plant-based diet in a dose-dependent manner.

Regular Supplementation with Antioxidants Rescues Doxorubicin-Induced Bone Deformities and Mineralization Delay in Zebrafish

Osteoporosis is characterized by an abnormal bone structure with low bone mass and degradation of microarchitecture. Oxidative stress induces imbalances in osteoblast and osteoclast activity, leading to bone degradation, a primary cause of secondary osteoporosis. Doxorubicin (DOX) is a widely used chemotherapy drug for treating cancer, known to induce secondary osteoporosis. The mechanism underlying DOX-induced bone loss is still not fully understood, but one of the relevant mechanisms is through a massive accumulation of reactive oxygen and nitrogen species (i.e., ROS and NOS) leading to oxidative stress. We investigated the effects of antioxidants Resveratrol and MitoTEMPO on DOX-induced bone impairment using the zebrafish model. DOX was shown to increase mortality, promote skeletal deformities, induce alterations on intestinal villi, impair growth and mineralization and significantly downregulate osteoblast differentiation markers osteocalcin 2 and osterix/sp7. Lipid peroxidation was significantly increased in DOX-supplemented groups as compared to control and antioxidants, suggesting ROS formation as one of the key factors for DOX-induced bone loss. Furthermore, DOX affected mineral contents, suggesting an altered mineral metabolism. However, upon supplementation with antioxidants, DOX-induced effects on mineral content were rescued. Our data show that supplementation with antioxidants effectively improves the overall growth and mineralization in zebrafish and counteracts DOX-induced bone anomalies.

Effects of Elephantopus scaber extract on growth, proximate composition, immunity, intestinal microbiota and resistance of the GIFT strain of Nile tilapia Oreochromis niloticus to Streptococcus agalactiae

This study aimed to investigate the effects of Elephantopus scaber extract on the GIFT (genetic improvement of farmed tilapia) strain of Nile tilapia Oreochromis niloticus. A total of 800 tilapia with an initial body weight of 1.34 ± 0.09 g each were randomly divided into five groups. The tilapia in the control group (E0 group) were fed on a basal diet only. Meanwhile, tilapia in the four experimental groups were fed on a basal diet supplemented with 1 g/kg (E1 group), 3 g/kg (E2 group), 5 g/kg (E3 group), and 7 g/kg (E4 group) of E. scaber extract for 10 weeks. Results showed that the survival rate was higher in the experimental groups than in the control group. Compared with the control group, some growth parameters (FW, WGR, SGR, VSI, and HSI) were significantly improved in the E1 group and E2 group. The crude lipid content in the dorsal muscle and liver was lower in the E1 group than in the control group. After E. scaber extract supplementation, activities of immunity-related enzymes (ACP, AKP, T-AOC, SOD, CAT, GSH-Px and LZM) in plasma, liver, spleen and head kidney, and expressions of immunity-related genes (IL-1β, IFN-γ, TNF-α, and CCL-3) in liver, spleen and head kidney showed various degrees of improvement, while MDA content and Hsp70 expression level were decreased. The survival rate of tilapia increased in all the supplementation groups after Streptococcus agalactiae treatment. E. scaber extract addition changed the species composition, abundance, and diversity of intestinal microbiota in tilapia. These results demonstrate that E. scaber extract supplementation in diet can improve the growth, immunity, and disease resistance of GIFT against S. agalactiae. E. scaber extract supplementation can also change intestinal microbiota and reduce crude lipid content in dorsal muscle and liver. The above indicators show that the optimal dose of E. scaber extract for GIFT is 1 g/kg.

Pharmacological characterization of a novel putative nootropic beta-alanine derivative, MB-005, in adult zebrafish

BACKGROUND

Cognitive deficits represent an urgent biomedical problem, and are commonly reduced by nootropic drugs. Animal models, including both rodents and zebrafish, offer a valuable tool for studying cognitive phenotypes and screening novel nootropics. Beta-alanine and its derivatives have recently been proposed to exert nootropic activity.

AIMS

This study aimed to characterize putative nootropic profile of a novel β-alanine analogue, 1,3-diaminopropane (MB-005), in adult zebrafish.

METHODS

Nootropic profile of MB-005 was assessed in adult zebrafish in the novel tank and conditioned place aversion (CPA) tests acutely, and in cued-learning plus-maze (PMT) tests chronically.

RESULTS/OUTCOMES

MB-005 did not alter zebrafish anxiety-like behavior or monoamine neurochemistry acutely, improved short-term memory in the CPA test, but impaired cognitive performance in both CPA and PMT tests chronically.

CONCLUSIONS/INTERPRETATION

This study reveals high sensitivity of zebrafish cognitive phenotypes to MB-005, suggesting it as a potential novel cognitive enhancer acutely, but raises concerns over its cognitive (and, possibly, other) side-effects chronically.

Acute behavioral and Neurochemical Effects of Novel N-Benzyl-2-Phenylethylamine Derivatives in Adult Zebrafish

Hallucinogenic drugs potently affect brain and behavior and have also recently emerged as potentially promising agents in pharmacotherapy. Complementing laboratory rodents, the zebrafish (Danio rerio) is a powerful animal model organism for screening neuroactive drugs, including hallucinogens. Here, we test a battery of ten novel N-benzyl-2-phenylethylamine (NBPEA) derivatives with the 2,4- and 3,4-dimethoxy substitutions in the phenethylamine moiety and the -OCH₃, -OCF₃, -F, -Cl, and -Br substitutions in the ortho position of the phenyl ring of the N-benzyl moiety, assessing their acute behavioral and neurochemical effects in the adult zebrafish. Overall, substitutions in the Overall, substitutions in the N-benzyl moiety modulate locomotion, and substitutions in the phenethylamine moiety alter zebrafish anxiety-like behavior, also affecting the brain serotonin and/or dopamine turnover. The 24H-NBOMe(F) and 34H-NBOMe(F) treatment also reduced zebrafish despair-like behavior. Computational analyses of zebrafish behavioral data by artificial intelligence identified several distinct clusters for these agents, including anxiogenic/hypolocomotor (24H-NBF, 24H-NBOMe, and 34H-NBF), behaviorally inert (34H-NBBr, 34H-NBCl, and 34H-NBOMe), anxiogenic/hallucinogenic-like (24H-NBBr, 24H-NBCl, and 24H-NBOMe(F)), and anxiolytic/hallucinogenic-like (34H-NBOMe(F)) drugs. Our computational analyses also revealed phenotypic similarity of the behavioral activity of some NBPEAs to that of selected conventional serotonergic and antiglutamatergic hallucinogens. In silico functional molecular activity modeling further supported the overlap of the drug targets for NBPEAs tested here and the conventional serotonergic and antiglutamatergic hallucinogens. Overall, these findings suggest potent neuroactive properties of several novel synthetic NBPEAs, detected in a sensitive in vivo vertebrate model system, the zebrafish, raising the possibility of their potential clinical use and abuse.

Feeding Rate and Protein Quality Differentially Affect Growth and Feeding Efficiency Response Variables of Zebrafish (Danio rerio)

Manipulating feeding rate and protein quality may improve growth and feeding efficiency of cultured species. However, whether feeding rate, protein quality, or their interaction has a greater effect on growth and feeding efficiency response variables is unknown. To determine whether feeding rate and protein quality individually or interactively affect growth and feeding efficiency, juvenile Zebrafish (Danio rerio) were either offered nutritionally similar diet consisting of either menhaden fishmeal protein or a 100% replacement of fishmeal with soybean meal-based protein restrictively or to satiation. Total length, weight, feed intake, and feed conversion ratio (FCR) were measured throughout the duration of the study. Protein quality and feeding rate individually and interactively affected feed intake and FCR: Zebrafish offered feed to satiation had higher growth and FCR than those fed restrictively, and Zebrafish fed soybean meal-based diet showed lower growth and higher FCR and feed intake compared to those fed fishmeal-based diet, although magnitude of response depended on feeding rate. These findings likely indicate lower digestibility of soybean meal or the presence of antinutritional factors in soybean meal that led to impaired nutrient absorption of fish offered soybean meal-based diet. Differences in measured response variables between protein qualities and feeding rates highlight the importance of determining interactive effects in nutritional studies.

Starter feed for carnivorous species as a practical replacement of bloodworms for a vertebrate model organism in ageing, the turquoise killifish Nothobranchius furzeri

The absence of a controlled diet is unfortunate in a promising model organism for ageing, the turquoise killifish (Nothobranchius furzeri Jubb, 1971). Currently captive N. furzeri are fed bloodworms but it is not known whether this is an optimal diet. Replacing bloodworms with a practical dry feed would reduce diet variability. In the present study, we estimated the nutritional value of the diet ingested by wild fish and determined the fish-body amino acid profile as a proxy for their nutritional requirements. We compared the performance of fish fed four commercial feeds containing 46%-64% protein to that achieved with bloodworms and that of wild fish. Wild fish target a high-protein (60%) diet and this is supported by their superior performance on high-protein diets in captivity. In contrast, feeds for omnivores led to slower growth, lower fecundity and unnatural liver size. In comparison to wild fish, a bloodworm diet led to lower body condition, overfeeding and male liver enlargement. Out of the four dry feeds tested, the fish fed Aller matched wild fish in body condition and liver size, and was comparable to bloodworms in terms of growth and fecundity. A starter feed for carnivorous species appears to be a practical replacement for bloodworms for N. furzeri. The use of dry feeds improved performance in comparison to bloodworms and thus may contribute to reducing response variability and improving research reproducibility in N. furzeri research.

Management of Hypercholesterolemia Through Dietary ß-glucans–Insights From a Zebrafish Model

Consumption of lipid-rich foods can increase the blood cholesterol content. β-glucans have hypocholesterolemic effect. However, subtle changes in their molecular branching can influence bioactivity. Therefore, a comparative investigation of the cholesterol-lowering potential of two β-glucans with different branching patterns and a cholesterol-lowering drug, namely simvastatin was undertaken employing the zebrafish (Danio rerio) model of diet-induced hypercholesterolemia. Fish were allocated to 5 dietary treatments; a control group, a high cholesterol group, two β-glucan groups, and a simvastatin group. We investigated plasma total cholesterol, LDL and HDL cholesterol levels, histological changes in the tissues, and explored intestinal transcriptomic changes induced by the experimental diets. Dietary cholesterol likely caused the suppression of endogenous cholesterol biosynthesis, induced dysfunction of endoplasmic reticulum and mitochondria, and altered the histomorphology of the intestine. The two β-glucans and simvastatin significantly abated the rise in plasma cholesterol levels and restored the expression of specific genes to alleviate the endoplasmic reticulum-related effects induced by the dietary cholesterol. Furthermore, the distinct patterns of transcriptomic changes in the intestine elicited by the oat and microalga β-glucans impacted processes such as fatty acid metabolism, protein catabolic processes, and nuclear division. Oat and microalgal β-glucans also altered the pattern of lipid deposition in the liver. Our study provides insights into the effectiveness of different β-glucans to alleviate dysfunctions in lipid metabolism caused by dietary cholesterol.

Zebrafish as an experimental model for the simulation of neurological and craniofacial disorders

Zebrafish have gained momentum as a leading experimental model in recent years. At present, the zebrafish vertebrate model is increasingly used due to its multifactorial similarities to humans that include genetic, organ, and cellular factors. With the emergence of novel research techniques that are very expensive, it is necessary to develop affordable and valid experimental models. This review aimed to highlight some of the most important similarities between zebrafish and humans by emphasizing the relevance of the first in simulating neurological disorders and craniofacial deformity.

The effects of dietary saturated fat source on weight gain and adiposity are influenced by both sex and total dietary lipid intake in zebrafish

The effects of saturated fat intake on obesity and cardiovascular health remain inconclusive, likely due in part to their varied nature and interactions with other nutrients. Investigating the synergistic effects of different saturated fat sources with other dietary lipid components will help establish more accurate nutritional guidelines for dietary fat intake. Over the past two decades, zebrafish (Danio rerio) have been established as an attractive model system to address questions regarding contributions of dietary lipid intake to diet-induced obesity in humans. The goal of the present study was to assess interactions of three different saturated fat sources (milk fat, palm oil, and coconut oil) with sex and total dietary lipid intake on weight gain and body composition in adult zebrafish. Larvae were raised on live feeds until 28 days post fertilization, and then fed a formulated maintenance diet until three months of age. An eight-week feeding trial was then initiated, in which zebrafish were fed nine experimental low- and high-fat diets varying in saturated fatty acid and long-chain polyunsaturated fatty acid content, in addition to a low-fat and high-fat control diet. At termination of the feeding trial, each treatment was evaluated according to body mass, moisture content, and adiposity. Sex and diet significantly interacted in their effects on body mass (P = 0.026), moisture content (P = 0.044), and adiposity (P = 0.035). The influence of saturated fat source on body mass was observed to be dependent on intake of total dietary lipid. In females, all three saturated fat sources had similar effects on adiposity. From these observations, we hypothesize that impacts of saturated fat intake on energy allocation and obesity-related phenotypes are influenced by both sex and intake of other dietary lipid components. Our results suggest that current nutritional guidelines for saturated fat intake may need to be re-evaluated and take sex-specific recommendations into consideration.

Standardized Reference Diets for Zebrafish: Addressing Nutritional Control in Experimental Methodology

The ideal of experimental methodology in animal research is the reduction or elimination of environmental variables or consistency in their application. In lab animals, diet has been recognized as a very influential response variable. Reproducibility in research using rodents required the development of a unique diet of consistent ingredient and nutrient composition to allow for cross-comparisons of lab results, spatially and temporally. These diets are commonly referred to as standard reference diets (SRDs). The established validity of published nutritional requirements combined with the cooperation of commercial partners led to species-specific reference diets commonly used by the research community. During the last several decades, zebrafish (Danio rerio) have become a widespread alternative animal model, but specific knowledge of their nutrition is lacking. We present a short-term approach for developing an SRD for zebrafish, similar to that eventually attained for rodents over decades. Imminent development of an open-formulation, commercially produced SRD for zebrafish will notably advance translational biomedical science. Expected final online publication date for the Annual Review of Nutrition, Volume 41 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Modulation of behavioral and neurochemical responses of adult zebrafish by fluoxetine, eicosapentaenoic acid and lipopolysaccharide in the prolonged chronic unpredictable stress model

Long-term recurrent stress is a common cause of neuropsychiatric disorders. Animal models are widely used to study the pathogenesis of stress-related psychiatric disorders. The zebrafish (Danio rerio) is emerging as a powerful tool to study chronic stress and its mechanisms. Here, we developed a prolonged 11-week chronic unpredictable stress (PCUS) model in zebrafish to more fully mimic chronic stress in human populations. We also examined behavioral and neurochemical alterations in zebrafish, and attempted to modulate these states by 3-week treatment with an antidepressant fluoxetine, a neuroprotective omega-3 polyunsaturated fatty acid eicosapentaenoic acid (EPA), a pro-inflammatory endotoxin lipopolysaccharide (LPS), and their combinations. Overall, PCUS induced severe anxiety and elevated norepinephrine levels, whereas fluoxetine (alone or combined with other agents) corrected most of these behavioral deficits. While EPA and LPS alone had little effects on the zebrafish PCUS-induced anxiety behavior, both fluoxetine (alone or in combination) and EPA restored norepinephrine levels, whereas LPS + EPA increased dopamine levels. As these data support the validity of PCUS as an effective tool to study stress-related pathologies in zebrafish, further research is needed into the ability of various conventional and novel treatments to modulate behavioral and neurochemical biomarkers of chronic stress in this model organism.

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.

Understanding complex dynamics of behavioral, neurochemical and transcriptomic changes induced by prolonged chronic unpredictable stress in zebrafish

Stress-related neuropsychiatric disorders are widespread, debilitating and often treatment-resistant illnesses that represent an urgent unmet biomedical problem. Animal models of these disorders are widely used to study stress pathogenesis. A more recent and historically less utilized model organism, the zebrafish (Danio rerio), is a valuable tool in stress neuroscience research. Utilizing the 5-week chronic unpredictable stress (CUS) model, here we examined brain transcriptomic profiles and complex dynamic behavioral stress responses, as well as neurochemical alterations in adult zebrafish and their correction by chronic antidepressant, fluoxetine, treatment. Overall, CUS induced complex neurochemical and behavioral alterations in zebrafish, including stable anxiety-like behaviors and serotonin metabolism deficits. Chronic fluoxetine (0.1 mg/L for 11 days) rescued most of the observed behavioral and neurochemical responses. Finally, whole-genome brain transcriptomic analyses revealed altered expression of various CNS genes (partially rescued by chronic fluoxetine), including inflammation-, ubiquitin- and arrestin-related genes. Collectively, this supports zebrafish as a valuable translational tool to study stress-related pathogenesis, whose anxiety and serotonergic deficits parallel rodent and clinical studies, and genomic analyses implicate neuroinflammation, structural neuronal remodeling and arrestin/ubiquitin pathways in both stress pathogenesis and its potential therapy.

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.

Diversity in Micromineral Distribution Within the Body of Ornamental Fish Species

This study was conducted to compare micromineral homeostasis across ornamental fish species. Ten different species (n = 3, total = 30) of live ornamental fish were randomly sampled from one big aquarium in a pet store in Belgium. All fish samples were dissected manually for the collection of targeted tissues. The tissue samples were ashed by microwave oven, and the extract was analyzed for copper (Cu), iron (Fe), and Zinc (Zn) by inductively coupled plasma mass spectrometry. Fe was associated with Cu in muscle tissue (p < 0.05), but neither of them were associated with Zn in the muscle. However, the three micromineral concentrations were correlated in the heart (p < 0.05). Similarly, all of them were correlated in the liver (p < 0.05), but none of them showed a significant association in the tail fin. Excess deposition of minerals in heart tissue is a new observation, and it is not known if this is meant as storage or rather the fish heart has a high requirement for microminerals. Storage in the tail fin should be interpreted as a sign of permanent deposition as a tool to dispose off toxic excess. The lack of correlation between the muscular concentrations of Zn on the one hand, and those of Fe and Cu on the other hand, further suggests that fish species distinctly differ in their micromineral metabolism. Although this exploratory study still leaves many questions unanswered, it points to the large diversity in micromineral metabolism among fish species.

Can Insect-Based Diets Affect Zebrafish (Danio rerio) Reproduction? A Multidisciplinary Study

Black Soldier Fly (BSF) meal is considered an alternative, emerging, and sustainable ingredient for aquafeed formulation. However, results on fish physiological responses are still fragmentary and often controversial, and no data are available on the effect of insect meal-based diets on fish reproduction. On this regard, zebrafish, with its relatively short life cycle, represents an ideal experimental model to explore this topic. In this study, female zebrafish were fed for 12 months on a control diet based on fish meal (FM) and fish oil and two experimental diets with full-fat BSF (Hermetia illucens) prepupae meal inclusion, to replace 25% and 50% of FM (BSF25 and BSF50). All diets were isonitrogenous, isolipidic, and isoenergetic. The effects of these two experimental diets on female's reproduction were investigated through a multidisciplinary approach, including the evaluation of growth, gonadosomatic index, spawned/fertilized eggs and hatching rate, adult female carcass and fertilized egg fatty acid composition, histological analysis of the ovary, spectroscopic macromolecular composition of class IV oocytes, and expression of genes involved in fish lipid metabolism in the liver. Results showed that while fish were perfectly able to cope with a 25% insect meal dietary inclusion, a 50% inclusion level caused the overexpression of genes involved in lipid metabolism, a general reduction in the number of spawned eggs, and differences in the frequency rate of previtellogenic oocytes, class III, IV, oocytes and postovulatory follicles and atretic oocytes, in the macromolecular composition of class IV oocytes, and in the fatty acid composition of the fertilized eggs, respect to control and 25% group.

Genetic and Genomic Advances in Developmental Models: Applications for Nutrition Research

There is increasing appreciation that dietary components influence and interact with genes important to metabolism. How such influences impact developmental regulation and programming or risks of chronic diseases remains unclear. Nutrition is recognized to affect development and chronic diseases, but our understanding about how genes essential to nutrient metabolism regulate development and impact risks of these diseases remains unclear. Historically, mammalian models, especially rodents such as rats and mice, have been the primary models used for nutrition and developmental nutrition science, although their complexity and relatively slow rate of development often compromise rapid progress in resolving fundamental, genetic-related questions. Accordingly, the objective of this review is to highlight the opportunities for developmental models in the context of uncovering the function of gene products that are relevant to human nutrition and provide the scientific bases for these opportunities. We present recent studies in zebrafish related to obesity as applications of developmental models in nutritional science. Although the control of external factors and dependent variables, such as nutrition, can be a challenge, suggestions for standardizations related to diet are made to improve consistency in findings between laboratories. The review also highlights the need for standardized diets across different developmental models, which could improve consistency in findings across laboratories. Alternative and developmental animal models have advantages and largely untapped potential for the advancement of nutrigenomics and nutritionally relevant research areas.

Zebrafish models of skeletal dysplasia induced by cholesterol biosynthesis deficiency

Human disorders of the post-squalene cholesterol biosynthesis pathway frequently result in skeletal abnormalities, yet our understanding of the mechanisms involved is limited. In a forward-genetic approach, we have found that a late-onset skeletal mutant, named kolibernu7 , is the result of a cis-acting regulatory mutation leading to loss of methylsterol monooxygenase 1 (msmo1) expression within pre-hypertrophic chondrocytes. Generated msmo1nu81 knockdown mutation resulted in lethality at larval stage. We demonstrated that this is a result of both cholesterol deprivation and sterol intermediate accumulation by creating a mutation eliminating activity of Lanosterol synthase (Lss). Our results indicate that double lssnu60;msmo1nu81 and single lssnu60 mutants survive significantly longer than msmo1nu81 homozygotes. Liver-specific restoration of either Msmo1 or Lss in corresponding mutant backgrounds suppresses larval lethality. Rescued mutants develop dramatic skeletal abnormalities, with a loss of Msmo1 activity resulting in a more-severe patterning defect of a near-complete loss of hypertrophic chondrocytes marked by col10a1a expression. Our analysis suggests that hypertrophic chondrocytes depend on endogenous cholesterol synthesis, and blocking C4 demethylation exacerbates the cholesterol deficiency phenotype. Our findings offer new insight into the genetic control of bone development and provide new zebrafish models for human disorders of the cholesterol biosynthesis pathway.

Good performance of turquoise killifish (Nothobranchius furzeri) on pelleted diet as a step towards husbandry standardization

Dietary alteration is one of the most universally effective aging interventions, making its standardization a fundamental need for model organisms in aging. In this dietetic study we address the current lack of standardized formulated diet for turquoise killifish Nothobranchius furzeri – a promising model organism. We first demonstrated that N. furzeri can be fully weaned at the onset of puberty onto a commercially available pelleted diet as the sole nutrition when kept in social tanks. We then compared nine somatic and six reproductive parameters between fish fed a typical laboratory diet - frozen chironomid larvae (bloodworms) and fish weaned from bloodworms to BioMar pellets. Both dietary groups had comparable somatic and reproductive performance. There was no difference between diet groups in adult body size, specific growth rate, condition or extent of hepatocellular vacuolation. Fish fed a pelleted diet had higher juvenile body mass and more visceral fat. Pellet-fed males had lower liver mass and possessed a lipid type of hepatocellular vacuolation instead of the prevailing glycogen-like vacuolation in the bloodworm-fed group. No considerable effect was found on reproductive parameters. The negligible differences between dietary groups and good acceptance of pellets indicate their suitability as a useful starting point for the development of standardized diet for Nothobranchius furzeri.

Both Dietary Ratio of n-6 to n-3 Fatty Acids and Total Dietary Lipid Are Positively Associated with Adiposity and Reproductive Health in Zebrafish

BACKGROUND

Controversial findings have been reported in human and animal studies regarding the influence of n-6 (ω-6) to n-3 (ω-3) fatty acid ratios on obesity and health. Two confounding factors may be related to interactions with other dietary lipid components or sex-specific differences in fatty acid metabolism.

OBJECTIVE

This study investigated main and interactive effects of total dietary lipid, ratio of n-6 to n-3 fatty acids, and sex on growth, adiposity, and reproductive health in wild-type zebrafish.

METHODS

Male and female zebrafish (3 wk old) were fed 9 diets consisting of 3 ratios of n-6 to n-3 fatty acids (1.4:1, 5:1, and 9.5:1) varied within 3 total lipid amounts (80, 110, and 140 g/kg) for 16 wk. Data were then collected on growth, body composition (determined by chemical carcass analysis), and female reproductive success (n = 32 breeding events/diet over 4 wk). Main and interactive effects of dietary lipid and sex were evaluated with regression methods. Significant differences within each dietary lipid component were relative to the intercept/reference group (80 g/kg and 1.4:1 ratio).

RESULTS

Dietary lipid and sex interacted in their effects on body weight (P = 0.015), total body length (P = 0.003), and total lipid mass (P = 0.029); thus, these analyses were stratified by sex. Female spawning success decreased as dietary total lipid and fatty acid ratio increased (P = 0.030 and P = 0.026, respectively). While total egg production was not associated with either dietary lipid component, females fed the 5:1 ratio produced higher proportions of viable embryos compared with the 1.4:1 ratio [median (95% CI): 0.915 (0.863, 0.956) vs 0.819 (0.716, 0.876); P < 0.001].

CONCLUSIONS

Further characterization of dietary lipid requirements will help define healthy balances of dietary lipid, while the sex-specific responses to dietary lipid identified in this study may partially explain sex disparities in the development of obesity and its comorbidities.

The zebrafish tail immobilization (ZTI) test as a new tool to assess stress-related behavior and a potential screen for drugs affecting despair-like states

BACKGROUND

Affective disorders, especially depression and anxiety, are highly prevalent, debilitating mental illnesses. Animal experimental models are a valuable tool in translational affective neuroscience research. A hallmark phenotype of clinical and experimental depression, the learned helplessness, has become a key target for 'behavioral despair'-based animal models of depression. The zebrafish (Danio rerio) has recently emerged as a promising novel organism for affective disease modeling and CNS drug screening. Despite being widely used to assess stress and anxiety-like behaviors, there are presently no clear-cut despair-like models in zebrafish.

NEW METHOD

Here, we introduce a novel behavioral paradigm, the zebrafish tail immobilization (ZTI) test, as a potential tool to assess zebrafish despair-like behavior. Conceptually similar to rodent 'despair' models, the ZTI protocol involves immobilizing the caudal half of the fish body for 5 min, leaving the cranial part to move freely, suspended vertically in a small beaker with water.

RESULTS

To validate this model, we used exposure to low-voltage electric shock, alarm pheromone, selected antidepressants (sertraline and amitriptyline) and an anxiolytic drug benzodiazepine (phenazepam), assessing the number of mobility episodes, time spent 'moving', total distance moved and other activity measures of the cranial part of the body, using video-tracking. Both electric shock and alarm pheromone decreased zebrafish activity in this test, antidepressants increased it, and phenazepam was inactive. Furthermore, a 5-min ZTI exposure increased serotonin turnover, elevating the 5-hydroxyindoleacetic acid/serotonin ratio in zebrafish brain, while electric shock prior to ZTI elevated both this and the 3,4-dihydroxyphenylacetic acid/dopamine ratios. In contrast, preexposure to antidepressants sertraline and amitriptyline lowered both ratios, compared to the ZTI test-exposed fish.

COMPARISON WITH EXISTINGMETHOD(S)

The ZTI test is the first despair-like experimental model in zebrafish.

CONCLUSIONS

Collectively, this study suggests the ZTI test as a potentially useful protocol to assess stress-/despair-related behaviors, potentially relevant to CNS drug screening and behavioral phenotyping of zebrafish.

Current basis and future directions of zebrafish nutrigenomics

This review investigates the current state of nutrigenomics in the zebrafish animal models. The zebrafish animal model has been used extensively in the study of disease onset and progression and associated molecular changes. In this review, we provide a synopsis of nutrigenomics using the zebrafish animal model. Obesity and dyslipidemia studies describe the genomics of dietary-induced obesity in relation to high-fat/high-calorie diets. Inflammation and cardiovascular studies describe dietary effects on the expression of acute inflammatory markers and resulting chronic inflammatory issues including atherosclerosis. We also evaluated the genomic response to bioactive dietary compounds associated with metabolic disorders. Carbohydrate metabolism and β-cell function studies describe the impacts of high-carbohydrate dietary challenges on nutritional programming. We also report tumorigenesis in relation to dietary carcinogen exposure studies that can result in permanent genomic changes. Vitamin and mineral deficiency studies demonstrate transgenerational genomic impacts of micronutrients in the diet and temporal expression changes. Circadian rhythm studies describe the relation between metabolism and natural temporal cycles of gene expression that impacts health. Bone formation studies describe the role of dietary composition that influences bone reabsorption regulation. Finally, this review provides future directions in the use of the zebrafish model for nutrigenomic and nutrigenetic research.

Microdiet Formulation with Phospholipid Modulate Zebrafish Skeletal Development and Reproduction

Dietary phospholipids' (PLs) content, origin, and profile are known to affect fish development and reproductive performance, but their effects in zebrafish (Danio rerio) nutrition are still poorly investigated. Therefore, this study aimed to assess the effect of practical microdiets containing plant-based and marine PL sources in zebrafish growth, survival, skeletal development, and reproductive performance. Reproductive performance was evaluated according to sperm motility, number of eggs, egg morphometry, hatching rate, and offspring standard length at 5 days postfertilization (dpf). For this purpose, seven microdiets were used, where two control diets were tested along with a supplementation with soybean lecithin (SL) as a plant-based PL source, and krill oil (KO) and copepod oil (CO) as marine PL sources, or in combinations (SLCO and SLKO). KO supplementation decreased larval growth performance and induced severe skeletal anomalies. SL supplementation reduced sperm total motility but improved offspring length at 5 dpf. CO supplementation increased sperm motility and the number of spawned eggs. Our results showed that a careful selection of the origin of dietary PL sources for microdiet formulation is critical to ensure adequate skeletal development and reproductive success. This study contributes to the improvement of zebrafish microdiet formulation and optimization of zebrafish husbandry practices.

Influence of Commercial and Laboratory Diets on Growth, Body Composition, and Reproduction in the Zebrafish Danio rerio

The value of the zebrafish (Danio rerio) as a model organism continues to expand. In developing the model, current feeding practice in zebrafish laboratories includes the use of commercially available diets. In this study, we compared outcomes in growth, body composition, and reproduction among zebrafish fed five highly utilized commercial diets and one formulated chemically defined reference diet. Wild-type zebrafish larvae were raised on live feed until 21 days postfertilization and then fed diets for 16 weeks. All fish received a daily ration of >5% of body weight (adjusted biweekly). Growth varied among diets throughout the feeding trial, and at study termination (week 16), significant differences among diets were observed for terminal weight gain, body condition index, body fat deposition, and reproductive outcomes. In addition, the proportion of viable embryos produced from females fed the formulated reference diet was high relative to the commercial diets. These data suggest that metabolic profiles, most likely reflecting nutrient/energy availability, utilization, and allocation, vary relative to diet in zebrafish. Undefined differences in metabolic profiles could result in erroneous predictions of health outcomes and make comparisons among laboratories more challenging. We recommend that dietary standards should be defined for zebrafish to support their common utility in biomedical research.

Scleraxis genes are required for normal musculoskeletal development and for rib growth and mineralization in zebrafish

Tendons are an essential part of the musculoskeletal system, connecting muscle and skeletal elements to enable force generation. The transcription factor scleraxis marks vertebrate tendons from early specification. Scleraxis-null mice are viable and have a range of tendon and bone defects in the trunk and limbs but no described cranial phenotype. We report the expression of zebrafish scleraxis orthologs: scleraxis homolog (scx)-a and scxb in cranial and intramuscular tendons and in other skeletal elements. Single mutants for either scxa or scxb, generated by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9), are viable and fertile as adult fish. Although scxb mutants show no obvious phenotype, scxa mutant embryos have defects in cranial tendon maturation and muscle misalignment. Mutation of both scleraxis genes results in more severe defects in cranial tendon differentiation, muscle and cartilage dysmorphogenesis and paralysis, and lethality by 2-5 wk, which indicates an essential function of scleraxis for craniofacial development. At juvenile and adult stages, ribs in scxa mutants fail to mineralize and/or are small and heavily fractured. Scxa mutants also have smaller muscle volume, abnormal swim movement, and defects in bone growth and composition. Scleraxis function is therefore essential for normal craniofacial form and function and vital for fish development.-Kague, E., Hughes, S. M., Lawrence, E. A., Cross, S., Martin-Silverstone, E., Hammond, C. L., Hinits, Y. Scleraxis genes are required for normal musculoskeletal development and for rib growth and mineralization in zebrafish.

Obese zebrafish: A small fish for a major human health condition

Obesity is becoming a silent worldwide epidemic, with a steady increase in both adults and children. To date, even though several drugs have been licensed for long-term obesity treatment, none of them are yet used in routine clinical practice. So far the only successful intervention has been behavioral therapy. A suitable and economic experimental model mimicking the human condition would therefore be extremely useful to evaluate preventive measures and novel treatments. Zebrafish are emerging as an important model system to study obesity and related metabolic disease. Remarkable similarities have been reported in lipid metabolism and the adipogenic pathway between zebrafish and mammals. Moreover, the zebrafish possesses a number of features-the relative inexpensiveness of animal husbandry, its optical transparency and the ability to produce a large number of offspring at low cost-that make it ideal for large-scale screening and for testing drugs and intervention. In this review, we summarize recent progress in using zebrafish as a model system to study obesity and obesity-related metabolic disorders. We describe several zebrafish models (in both larvae and adult animals) that develop obesity and non-alcoholic fatty liver disease (NAFLD) using different approaches, including gene manipulation, diet manipulation and modification of microbiota composition. For these models, we have outlined the specific aspects related to obesity and its development and we have summarized their advantages and limitations.

Reversibility of Proliferative Thyroid Lesions Induced by Iodine Deficiency in a Laboratory Zebrafish Colony

A laboratory zebrafish colony developed red masses, predominantly under the jaw, in a significant portion of the population. The masses were diagnosed histopathologically as thyroid follicular hyperplasia, adenoma, or carcinoma in accordance with published morphologic criteria. After switching to a higher iodine brand of salt used to maintain a low level of salinity within the water system and a small diet change, the thyroid lesions regressed dramatically. Within 5 months the masses were no longer grossly visible. At the population level, external evaluations and histopathological assessments of whole-body sections document a regression in the prevalence of thyroid neoplasia and hyperplasia to normal thyroid conformation by 11 months after salt change. These findings suggest that a wide range of proliferative thyroid lesions, including neoplasms, in zebrafish may be hormone-dependent, even following lesion development. In addition, these results suggest that zebrafish have an adaptive ability to absorb iodine from water and food, which should be considered in discussions to standardize diets and when describing environmental parameters in publications.

The Impact of Two Different Cold-Extruded Feeds and Feeding Regimens on Zebrafish Survival, Growth and Reproductive Performance

Zebrafish (Danio rerio) is one of the top model organisms used in biomedical research. Therefore, it is fundamental that zebrafish facilities continuously improve husbandry methods to provide fish with the best physiological and welfare conditions that suit each experimental purpose. Nutrition is a husbandry aspect that needs further optimization, as it greatly affects growth, reproduction, health and behaviour. Here, we have compared the impact of different feeding regimens on zebrafish survival, growth and reproductive performance. Mutant and wild-type zebrafish were raised using several combinations of two cold-extruded processed feeds—Skretting^®GemmaMicro and Sparos^®Zebrafeed—and one live feed (rotifers). Zebrafeed^® outperformed GemmaMicro^® in terms of survival rate, and embryo viability was also higher when the spawners were fed with Zebrafeed^® either from larval stage or upon sexual maturation. In contrast, GemmaMicro^® favoured growth, both in size and weight. The use of rotifers until 60 days post-fertilization improved survival of fish co-fed with GemmaMicro^®, while delaying their growth. Zebrafeed^® performance was not affected by co-feeding rotifers. Overall, we showed that different nutritional formulas affect physiological parameters, allowing for the establishment of feeding protocols adapted to the objectives of each facility. At the same time, we validated Skretting^®GemmaMicro and Sparos^®Zebrafeed as two commercially available feeds that are well suited for zebrafish nutrition in a laboratory environment.

Changes to Extender, Cryoprotective Medium, and In Vitro Fertilization Improve Zebrafish Sperm Cryopreservation

Sperm cryopreservation is a highly efficient method for preserving genetic resources. It extends the reproductive period of males and significantly reduces costs normally associated with maintenance of live animal colonies. However, previous zebrafish (Danio rerio) cryopreservation methods have produced variable outcomes and low post-thaw fertilization rates. To improve post-thaw fertilization rates after cryopreservation, we developed a new extender and cryoprotective medium (CPM), introduced quality assessment (QA), determined the optimal cooling rate, and improved the post-thaw in vitro fertilization process. We found that the hypertonic extender E400 preserved motility of sperm held on ice for at least 6 h. We implemented QA by measuring sperm cell densities with a NanoDrop spectrophotometer and sperm motility with computer-assisted sperm analysis (CASA). We developed a CPM, RMMB, which contains raffinose, skim milk, methanol, and bicine buffer. Post-thaw motility indicated that the optimal cooling rate in two types of cryogenic vials was between 10 and 15°C/min. Test thaws from this method produced average motility of 20% ± 13% and an average post-thaw fertilization rate of 68% ± 16%.

Inadequate Dietary Phosphorus Levels Cause Skeletal Anomalies and Alter Osteocalcin Gene Expression in Zebrafish

Phosphorus (P) is an essential mineral for the development and maintenance of the vertebrate skeletal system. Modulation of P levels is believed to influence metabolism and the physiological responses of gene expression. In this study, we investigated the influence of dietary P on skeletal deformities and osteocalcin gene expression in zebrafish (Danio rerio), and sought to determine appropriate levels in a diet. We analyzed a total of 450 zebrafish within 31 days of hatching. Animals were distributed in a completely randomized experimental design that consisted of five replications. After an eight-week experiment, fish were diaphanized to evaluate cranial and spinal bone deformities. Increases in dietary phosphorus were inversely proportional to the occurrence of partial spine fusions, the absence of spine fusions, absence of parallelism between spines, intervertebral spacing, vertebral compression, scoliosis, lordosis, ankylosis, fin caudal insertion, and craniofacial deformities. Additionally, osteocalcin expression was inversely correlated to P levels, suggesting a physiological recovery response for bone mineralization deficiency. Our data showed that dietary P concentration was a critical factor in the occurrence of zebrafish skeletal abnormalities. We concluded that 1.55% P in the diet significantly reduces the appearance of skeletal deformities and favors adequate bone mineralization through the adjustment of osteocalcin expression.

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

The lack of standardized diet for laboratory animals can have profound effects on animal health and lead to less reproducible research outcomes. Live diets are commonly used in zebrafish culture and, although they are a more natural feed than flake or pellet food, are also a potential source of pathogens and toxic compounds. Heavy metals are a group of such compounds, which can accumulate in fish leading to developmental abnormalities, reduced growth, and increased rates of mortality. Two to three weeks after feeding adult zebrafish a new lot of nonhatching decapsulated brine shrimp cysts (Decaps), embryos at the University of Minnesota Zebrafish Core Facility (ZCF) and the University of Utah Centralized Zebrafish Animal Resource (CZAR) began to exhibit an orange color in the yolk, and larval health began to decline. The concentration of chromium in the Decaps (69.6 mg/kg) was more than 30 times that of other zebrafish diets tested (up to 2.1 mg/kg) and is thought to be the cause of the observed symptoms. Within 3 weeks of removing the Decaps from the feeding regimen, the orange coloration in the yolks began to diminish, the morphological abnormalities began to subside, and larval survival rates began to increase. Thus, implementation of standardized zebrafish diets and regular feed-quality testing may help to prevent the introduction of contaminants to zebrafish research facilities.