Inbred strains of zebrafish exhibit variation in growth performance and myostatin expression following fasting

The effect of laboratory diet and feeding on growth parameters in juvenile zebrafish

Despite being one of the most used laboratory species in biomedical, behavioral and physiological research, the nutritional requirements of zebrafish (Danio rerio) are poorly understood, and no standardized laboratory diet exists. Diet and feeding regimen can substantially impact the welfare of the fish and, in turn, experimental reproducibility. Consequently, the establishment of a standardized diet and feeding protocol for laboratory zebrafish is imperative to enhance animal welfare, guarantee research reproducibility and advance the economic and environmental sustainability of laboratory dietary practices. Here the aim of this systematic review is to provide an overview of the parameters that need to be standardized in future nutritional studies to facilitate future meta-analyses for confirmation of an optimal juvenile diet for growth. A comprehensive search was conducted in PubMed and Scopus to identify relevant studies published up to August 2023, and the studies were selected on the basis of the predefined inclusion/exclusion criteria. The databases yielded a total of 1,065 articles, of which 14 were included in this review. We conducted data extraction and risk-of-bias analysis in the included studies. Statistical comparisons for specific growth rate, weight gain (%) and length gain (%) parameters were performed to determine the optimal feed for enhanced juvenile growth. We identified significant heterogeneity and caveats to our findings owing to a lack of standardization of experimental conditions in nutritional studies. Our findings highlight an urgent need for research on zebrafish nutrition. Therefore, the standardized parameters we have reported here represent a critical starting point for studies.

Comparison of baseline cataract rates in AB and TL wildtype zebrafish strains

Zebrafish are an outstanding model for assessing the involvement of genes in paediatric cataracts. Gene discovery for cataracts is enhanced by manipulation of the genome of zebrafish embryos and comparing the phenotypes of mutant progeny with the wildtype embryos. However, wildtype laboratory fish can also develop cataracts, potentially confounding the results. In this study, we compared the baseline cataract rate between two commonly used wildtype laboratory strains, AB and TL, and also an outbred transgenic line with mCherry reporter. We assessed a total of 805 lens images of fish at 4 days post-fertilisation for cataracts and scored each cataract observed as mild, moderate or severe. We found that the AB strain had a cataract rate of 16.2%, TL had 8.9%, and mCherry had 0.7% and these rates were significantly different. We found that TL strain had a lower rate of mild cataracts than AB fish, however, the rate of moderate and severe phenotypes in the AB and the TL strain was similar. Overall, we showed that the baseline cataract rate varies significantly between the strains housed in a single facility and conclude that baseline rates of cataracts should be assessed when planning experiments to assess the genetic causes of cataracts.

The effects of P-glycoprotein induction on ivermectin-induced behavioural alterations in zebrafish (Danio rerio) under varying diets

The neuroprotective effects of inducing the blood-brain barrier ATP-binding cassette protein transporter P-glycoprotein (P-gp) with clotrimazole (CTZ) in both fed and fasted zebrafish (Danio rerio) against the CNS-toxicant ivermectin (IVM, 22,23-dihydro avermectin B1a + 22,23-dihydro avermectin B1b) were examined. Zebrafish were administered 2 μmol/kg IVM intraperitoneally, and various behavioural assays (swimming performance, exploratory behaviour, olfactory responses, motor coordination, and escape responses) were used to measure neurological dysfunction. IVM administration alone caused a decrease in mean swim speed (91 % of controls), maximal speed (71 %), passage rate (81 %), 90° turns (81 %), and response to food stimulus (39 %). IVM exposure also increased the percent time that fish spent immobile (45 % increase over controls) and the percent of lethargic fish (40 % increase). Fish administered 30 μmol/kg of the P-gp inducer CTZ intraperitoneally 3 d prior to IVM exposure exhibited a change in only the % time spent immobile. These data indicate that P-gp induction may be limited in protecting the zebrafish CNS from IVM over baseline. Fasted fish did not differ from fed fish in the effects of IVM on behaviour, and no differences were seen following P-gp induction with CTZ. These results suggest that this chemical defence system is not downregulated when fish are challenged with limited energy availability.

Assessing Drug Administration Techniques in Zebrafish Models of Neurological Disease

Neurological diseases, including neurodegenerative and neurodevelopmental disorders, affect nearly one in six of the world's population. The burden of the resulting deaths and disability is set to rise during the next few decades as a consequence of an aging population. To address this, zebrafish have become increasingly prominent as a model for studying human neurological diseases and exploring potential therapies. Zebrafish offer numerous benefits, such as genetic homology and brain similarities, complementing traditional mammalian models and serving as a valuable tool for genetic screening and drug discovery. In this comprehensive review, we highlight various drug delivery techniques and systems employed for therapeutic interventions of neurological diseases in zebrafish, and evaluate their suitability. We also discuss the challenges encountered during this process and present potential advancements in innovative techniques.

Optimizing assays of zebrafish larvae swimming performance for drug discovery

INTRODUCTION

Zebrafish larvae are one of the few vertebrates amenable to large-scale drug discovery screens. Larval swimming behavior is often used as an outcome variable and many fields of study have developed assays for evaluating swimming performance. An unintended consequence of this wide interest is that details related to assay methodology and interpretation become scattered across the literature. The aim of this review is to consolidate this information, particularly as it relates to high-throughput approaches.

AREAS COVERED

The authors describe larval swimming behaviors as this forms the basis for understanding their experimentally evoked swimming or spontaneous activity. Next, they detail how swimming activity can serve as an outcome variable, particularly in the multi-well formats used in large-scale screening studies. They also highlight biological and technical factors that can impact the sensitivity and variability of these measurements.

EXPERT OPINION

Careful attention to animal husbandry, experimental design, data acquisition, and interpretation of results can improve screen outcomes by maximizing swimming activity while minimizing intra- and inter-larval variability. The development of more sensitive, quantitative methods of assessing swimming performance that can be incorporated into high-throughput workflows will be important in order to take full advantage of the zebrafish model.

Nutritional status affects Igf1 regulation of skeletal muscle myogenesis, myostatin, and myofibrillar protein degradation pathways in gopher rockfish (Sebastes carnatus)

Insulin-like growth factor-1 (Igf1) regulates skeletal muscle growth in fishes by increasing protein synthesis and promoting muscle hypertrophy. When fish experience periods of insufficient food intake, they undergo slower muscle growth or even muscle wasting, and those changes emerge in part from nutritional modulation of Igf1 signaling. Here, we examined how food deprivation (fasting) modulates Igf1 regulation of liver and skeletal muscle gene expression in gopher rockfish (Sebastes carnatus), a nearshore rockfish of importance for commercial and recreational fisheries in the northeastern Pacific Ocean, to understand how food limitation impacts Igf regulation of muscle growth pathways. Rockfish were either fed or fasted for 14 d, after which a subset of fish from each group was treated with recombinant Igf1 from sea bream (Sparus aurata). Fish that were fasted lost body mass and had lower body condition, reduced hepatosomatic index, and lower plasma Igf1 concentrations, as well as a decreased abundance of igf1 gene transcripts in the liver, increased hepatic mRNAs for Igf binding proteins igfbp1a, igfbp1b, and igfbp3a, and decreased mRNA abundances for igfbp2b and a putative Igf acid labile subunit (igfals) gene. In skeletal muscle, fasted fish showed a reduced abundance of intramuscular igf1 mRNAs but elevated gene transcripts encoding Igf1 receptors A (igf1ra) and B (igf1rb), which also showed downregulation by Igf1. Fasting increased skeletal muscle mRNAs for myogenin and myostatin1, as well as ubiquitin ligase F-box only protein 32 (fbxo32) and muscle RING-finger protein-1 (murf1) genes involved in muscle atrophy, while concurrently downregulating mRNAs for myoblast determination protein 2 (myod2), myostatin2, and myogenic factors 5 (myf5) and 6 (myf6 encoding Mrf4). Treatment with Igf1 downregulated muscle myostatin1 and fbxo32 under both feeding conditions, but showed feeding-dependent effects on murf1, myf5, and myf6/Mrf4 gene expression indicating that Igf1 effects on muscle growth and atrophy pathways is contingent on recent food consumption experience.

Exposure to an environmentally relevant concentration of 17α-ethinylestradiol disrupts craniofacial development of juvenile zebrafish

Endocrine disrupting chemicals (EDCs) can interact with native hormone receptors to interfere with and disrupt hormone signalling that is necessary for a broad range of developmental pathways. EDCs are pervasive in our environment, in particular in our waterways, making aquatic wildlife especially vulnerable to their effects. Many of these EDCs are able to bind to and activate oestrogen receptors, causing aberrant oestrogen signalling. Craniofacial development is an oestrogen-sensitive process, with oestrogen receptors expressed in chondrocytes during critical periods of development. Previous studies have demonstrated a negative effect of high concentrations of oestrogen on early craniofacial patterning in the aquatic model organism, the zebrafish (Danio rerio). In order to determine the impacts of exposure to an oestrogenic EDC, we exposed zebrafish larvae and juveniles to either a high concentration to replicate previous studies, or a low, environmentally relevant concentration of the oestrogenic contaminant, 17α-ethinylestradiol. The prolonged / chronic exposure regimen was used to replicate that seen by many animals in natural waterways. We observed changes to craniofacial morphology in all treatments, and most strikingly in the larvae-juveniles exposed to a low concentration of EE2. In the present study, we have demonstrated that the developmental stage at which exposure occurs can greatly impact phenotypic outcomes, and these results allow us to understand the widespread impact of oestrogenic endocrine disruptors. Given the conservation of key craniofacial development pathways across vertebrates, our model can further be applied in defining the risks of EDCs on mammalian organisms.

P-glycoprotein inhibition affects ivermectin-induced behavioural alterations in fed and fasted zebrafish (Danio rerio)

The role of the blood-brain barrier ATP-binding cassette protein transporter P-glycoprotein (P-gp) in protecting zebrafish (Danio rerio) from the central nervous system neurotoxicant ivermectin (IVM, 22,23-dihydroavermectin B1a + 22,23-dihydroavermectin B1b) was examined in the absence and presence of the competitive inhibitor cyclosporin A (CsA). Zebrafish injected intraperitoneally with 1, 2, 5, or 10 µmol/kg IVM exhibited mortality 30 min following administration at the highest dose. At sublethal doses > 1 µmol/kg, IVM altered the swimming performance, exploratory behaviour, motor coordination, escape response and olfactory response in exposed fish. When fish were exposed to IVM in the presence of CsA, alterations in swimming and behaviours increased significantly and at the highest IVM/CsA ratio resulted in a complete lack of exploratory and olfactory behaviours. In separate experiments, fish were either fed or fasted, and the effects of IVM and CsA administration were examined. The effects of IVM administration and the exacerbated effects seen with CsA co-administration were not affected by fasting. This study provides evidence that P-gp provides a protective role in the BBB of fish against environmental neurotoxicants. The results also show that P-gp activity is maintained even under conditions of food deprivation, suggesting that this chemical defence system is prioritized over other energy expenditures during diet limitation.

GENETIC VARIABILITY AND REPRODUCTIVE CHARACTERISTICS OF ZEBRAFISH (Cyprinidae Danio rerio) STOCKS

Specimens of cultured zebrafish acquired from different fish farms in Brazil may show genetic variability and alteration in allele frequency due to genetic drift and selective pressure in a captive environment, resulting in the differentiation of productive and reproductive characteristics. The aim of this study was to evaluate the genetic variability and reproductive characteristics of 180 zebrafish specimens from six Brazilian fish farms. A deviation from the Hardy-Weinberg equilibrium was observed in all evaluated stocks. Differentiation among stocks was observed in the amount of genetic variability with respect to observed heterozygosity and the inbreeding coefficient (FIS). Genetic distance between stocks was determined through the Fst index, and the formation of four distinct groups was observed by plotting the dendrogram based on Nei’s genetic distance. Differences were observed among reproductive parameters, such as the average number of eggs per female and hatchability. This second parameter proved to be related to the level of inbreeding of the population, whereas this effect was not observed for spawning frequency. We conclude that zebrafish stocks from the 6 different Brazilian fish farms present significant genetic and phenotypic variability. The genetic structure affects fecundity and should be considered when carrying out work where reproductive rates are evaluated.

Evaluation of fentanyl toxicity and metabolism using a zebrafish model

The increased abuse of novel drugs has created a critical need for cheap and rapid in vivo models to understand whole organism drug-induced toxicity and metabolic impacts. One such model is zebrafish, which share many similarities to human. Assays have been developed for behavioral, toxicity, and metabolism elucidation following chemical exposure. The zebrafish model provides the advantage of assessing these parameters within a single study. Previous zebrafish studies have evaluated the behavioral effects of fentanyl, but not developmental toxicity and its relation to metabolism. In this study, we evaluate the effects of fentanyl on the development of wild-type (TL strain) zebrafish and its metabolism over 4 days. Fertilized eggs were exposed to six concentrations of fentanyl (0.01, 0.1, 1, 10, 50, and 100 μM) through embryo media incubated at 28-29°C. Observations included egg coagulation, somite formation, heartbeat, tail and yolk morphology, pericardial formation, and swim bladder inflation. The incubation media was analyzed for the presence of metabolites using a targeted metabolomics approach. Fentanyl concentration caused significant effects on survival and development, with notable defects to the tail, yolk, and pericardium at 50 and 100 μM. Despropionyl fentanyl (4-ANPP), β-hydroxy fentanyl, and norfentanyl were detected in zebrafish larvae. We present a single in vivo model to assess toxicity and metabolism of fentanyl exposure in a vertebrate model system. Our findings provide a foundation for further investigations into fentanyl's mechanism of action and translation to human drug exposure.

Different influences of anxiety models, environmental enrichment, standard conditions and intraspecies variation (sex, personality and strain) on stress and quality of life in adult and juvenile zebrafish: A systematic review

Antagonist and long-lasting environmental manipulations (EM) have successfully induced or reduced the stress responses and quality of life of zebrafish. For instance, environmental enrichment (EE) generally reduces anxiety-related behaviours and improves immunity, while unpredictable chronic stress (UCS) and aquarium-related stressors generate the opposite effects. However, there is an absence of consistency in outcomes for some EM, such as acute exposure to stressors, social enrichment and some items of structural enrichment. Therefore, considering intraspecies variation (sex, personality, and strain), increasing intervention complexity while improving standardisation of protocols and contemplating the possibility that EE may act as a mild stressor on a spectrum between too much (UCS) and too little (standard conditions) stress intensity or stimulation, would reduce the inconsistencies of these outcomes. It would also help explore the mechanism behind stress resilience and to standardise EM protocols. Thus, this review critically analyses and compares knowledge existing over the last decade concerning environmental manipulations for zebrafish and the influences that sex, strain, and personality may have on behavioural, physiological, and fitness-related responses.

A fish is not a mouse: understanding differences in background genetics is critical for reproducibility

Poorly controlled background genetics in animal models contributes to the lack of reproducibility that is increasingly recognized in biomedical research. The laboratory zebrafish, Danio rerio, has been an important model organism for decades in many research areas, yet inbred strains and traditionally managed outbred stocks are not available for this species. Sometimes incorrectly referred to as 'inbred strains' or 'strains', zebrafish wild-type lines possess background genetics that are often not well characterized, and breeding practices for these lines have not been consistent over time or among institutions. In this Perspective, we trace key milestones in the history of one of the most widely used genetic backgrounds, the AB line, to illustrate the dynamic complexity within an example background that is largely invisible when reading the scientific literature. Failure to adequately control for genetic background compromises the validity of experimental outcomes. We therefore propose that authors provide as much specific detail about the origin and genetic makeup of zebrafish lines as is reasonable and possible, and that the terms used to describe background genetics be applied in a way that is consistent with other fish and mammalian model organisms. We strongly encourage the adoption of genetic monitoring for the characterization of existing zebrafish lines, to help detect genetic contamination in breeding colonies and to verify the level of genetic heterogeneity in breeding colonies over time. Careful attention to background genetics will improve transparency and reproducibility, therefore improving the utility of the zebrafish as a model organism.

Method Standardization for Conducting Innate Color Preference Studies in Different Zebrafish Strains

The zebrafish has a tetrachromatic vision that is able to distinguish ultraviolet (UV) and visible wavelengths. Recently, zebrafish color preferences have gained much attention because of the easy setup of the instrument and its usefulness to screen behavior-linked stimuli. However, several published papers dealing with zebrafish color preferences have contradicting results that underscore the importance of method standardization in this field. Different laboratories may report different results because of variations in light source, color intensity, and other parameters such as age, gender, container size, and strain of fish. In this study, we aim to standardize the color preference test in zebrafish by measuring light source position, light intensity, gender, age, animal size to space ratio, and animal strain. Our results showed that color preferences for zebrafish are affected by light position, age, strain, and social interaction of the fish, but not affected by fish gender. We validated that ethanol can significantly induce color preference alteration in zebrafish which may be related to anxiety and depression. We also explored the potential use of the optimized method to examine color preference ranking and index differences in various zebrafish strains and species, such as the tiger barb and glass catfish. In conclusion, zebrafish color preference screening is a powerful tool for high-throughput neuropharmacological applications and the standardized protocol established in this study provides a useful reference for the zebrafish research community.

Inhibitory control in zebrafish, Danio rerio

We assessed whether zebrafish, Danio rerio, display inhibitory control using a simple and rapid behavioural test. Zebrafish were exposed to a prey stimulus placed inside a transparent tube, which initially elicited attack behaviour. However, zebrafish showed a rapid reduction in the number of attacks towards the prey, which indicated the ability to inhibit their foraging behaviour. Zebrafish also exhibited mnemonic retention of foraging inhibition, as indicated by a reduced number of attacks in a subsequent exposure to the unreachable prey. The ability to inhibit the foraging behaviour varied across three genetically separated wild-type strains and across different individuals within strains, suggesting that zebrafish show heritable within-species differences in inhibitory control. Our behavioural test might be suitable for screening large zebrafish populations in mutational studies and assessing the effects of pharmacologically active substances on inhibitory control.

Which Zebrafish Strains Are More Suitable to Perform Behavioral Studies? A Comprehensive Comparison by Phenomic Approach

Wild-type (WT) zebrafish are commonly used in behavioral tests, however, the term WT corresponds to many different strains, such as AB, Tübingen long fin (TL), and Wild Indian Karyotype (WIK). Since these strains are widely used, there has to be at least one study to demonstrate the behavioral differences between them. In our study, six zebrafish strains were used, which are AB, absolute, TL, golden, pet store-purchased (PET), and WIK zebrafishes. The behavior of these fishes was tested in a set of behavioral tests, including novel tank, mirror-biting, predator avoidance, social interaction, and shoaling tests. From the results, the differences were observed for all behavioral tests, and each strain displayed particular behavior depending on the tests. In addition, from the heatmap and PCA (principal component analysis) results, two major clusters were displayed, separating the AB and TL zebrafishes with other strains in another cluster. Furthermore, after the coefficient of variation of each strain in every behavioral test was calculated, the AB and TL zebrafishes were found to possess a low percentage of the coefficient of variation, highlighting the strong reproducibility and the robustness of the behaviors tested in both fishes. Each zebrafish strain tested in this experiment showed specifically different behaviors from each other, thus, strain-specific zebrafish behavior should be considered when designing experiments using zebrafish behavior.

A Comparison of Isogenic Homozygous Clone and Wildtype Zebrafish (Danio rerio): Survival and Developmental Responses to Low pH Conditions

The value of bioassays as analytical methods for assessing the potency of particular stressors on live animal models depends on the precision of their results, which are greatly influenced by the choice of test subjects. The genetic makeup of experimental subjects varies, and, as such, so will their responses to the test environment. Genetic diversity of test populations may contribute to statistical variability; therefore, the use of genetically similar subjects may enhance the utility of bioassays. This study addresses the efficacy of using isogenic homozygous zebrafish (Danio rerio) as subjects for bioassays. Stress responses (acidic conditions) were compared during early development for gynogenetically produced isogenic homozygous line of zebrafish (C32) and wildtype (WT) zebrafish. Experiments evaluated early life stage milestones after exposure to low pH in water of a different electrolyte composition. Because the isogenic homozygous clonal (IHC) fish possessed far less genetic variability than the WT fish tested, it was predicted that the IHC fish would exhibit less variability in their response to stress. Although we found no significant differences in the variability between the responses of the IHC and WT fish, pH and water hardness level had a differential effect on the two groups. Simple strain differences may be the probable cause of the response differences to environmental stress. Factors that may affect stress response, such as heterogeneity, co-adapted gene complexes, and domestication, are discussed. Our findings and review of recent zebrafish literature stress the need for researchers to carefully consider breeding histories and trait characteristics for each potential test subject to maximize the sensitivity of the assay.

Swimming capability of zebrafish is governed by water temperature, caudal fin length and genetic background

Several zebrafish strains such as AB, Tübingen (TU), Wild India Kolkata (WIK) and Tupfel long fin (TL) have been established for genetic study. Each strain has its morphological and behavioral traits. Motor traits, however, have not been explored in zebrafish strains. We here applied a treadmill for fish (swimmill) and measured swimming capability of adult zebrafish by critical swimming speed, which is the maximum water velocity in which fish can keep swimming. First, we confirmed that swimming capability does not vary between female and male. Second, we found that the appropriate water temperature for swimming was between 16 and 30 °C. Third, our fin clip experiments using long-finned zebrafish revealed that they can exhibit high swimming capability when the caudal fin length was set between 3 and 10 mm, implying that long-finned zebrafish are unfavorable for fast swimming. Finally, we compared swimming capability of several zebrafish strains and demonstrated that WIK fish was significantly less capable of swimming despite that they have short caudal fin (~9 mm). The offspring of WIK fish were less capable of swimming, while hybrids of WIK and TU showed high swimming performance comparable to TU. Thus, lower swimming capability of WIK strain is inheritable as a motor trait.

Effects of fasting on the central expression of appetite-regulating and reproductive hormones in wild-type and Casper zebrafish (Danio rerio)

Appetite and reproduction are closely related functions that are both regulated by brain hormones. Appetite stimulators include orexin and neuropeptide Y (NPY), and reproductive hormones include gonadotropin-releasing hormone (GnRH), gonadotropin-inhibitory hormone (GnIH), kisspeptin, and neurokinin B (NKB). GnRH stimulates the secretion of pituitary gonadotropes, and kisspeptin and GnIH modulate this action. Kisspeptin secretion is further controlled by neurokinin B (NKB) and dynorphin A (Dyn). To better understand the mechanisms regulating appetite and reproduction in fish, we examined the effects of fasting, reproductive stage, gender, and strain on the brain mRNA expression of appetite (orexin and NPY) and reproductive (GnRH, kisspeptin, GnIH, and NKB) hormones in zebrafish. In order to compare strains, we used both wild-type and transparent Casper zebrafish. In female wild-type zebrafish, fasting increased the expression of all hormones investigated, with the exception of Kiss2. Only NPY and Kiss2 were increased in male wild-type zebrafish during fasting. In Casper zebrafish, only GnIH and NKB in males were affected by fasting, suggesting that Casper fish may be more resistant to fasting than wild fish. Fasting increased expressions of orexin, GnRH2, Kiss1, GnIH and NKB in wild-type females with more eggs or larger eggs relative to body weight, compared to those with fewer or smaller eggs, suggesting that more mature females are more affected by fasting. No significant interactions of fasting and reproductive stage were noted in female Casper fish. To investigate whether differences between Casper and wild-type fish were due to genes involved in pigmentation, we compared the brain mRNA expressions of enzymes involved in melanin synthesis (tyrosinase and tyrosine hydroxylase - TH), melanocortin receptors (MC3R and MC4R), and the melanocortin precursor (proopiomelanocortin - POMC) between the two strains. Casper zebrafish had lower levels of MC3R, tyrosinase, TH1, TH2, and POMC than wild-type fish. Overall, our results suggest the existence of gender- and reproductive stage-specific, as well as strain-specific variations in the mechanisms regulating feeding and reproduction in zebrafish, and that the melanocortin system and melanin pathways may be in part responsible for these differences between strains.

Sex differences in behavior and neuropharmacology of zebrafish

Sex is an important variable in biomedical research. The zebrafish (Danio rerio) is increasingly utilized as a powerful new model organism in translational neuroscience and pharmacology. Mounting evidence indicates important sex differences in zebrafish behavioral and neuropharmacological responses. Here, we discuss the role of sex in zebrafish central nervous system (CNS) models, their molecular mechanisms, recent findings and the existing challenges in this field. We also emphasize the growing utility of zebrafish models in translational neuropharmacological research of sex differences, fostering future CNS drug discovery and the search for novel sex-specific therapies. Finally, we highlight the interplay between sex and environment in zebrafish models of sex-environment correlations as an important strategy of CNS disease modeling using this aquatic organism.

The role of intraspecies variation in fish neurobehavioral and neuropharmacological phenotypes in aquatic models

Intraspecies variation is common in both clinical and animal research of various brain disorders. Relatively well-studied in mammals, intraspecies variation in aquatic fish models and its role in their behavioral and pharmacological responses remain poorly understood. Like humans and mammals, fishes show high variance of behavioral and drug-evoked responses, modulated both genetically and environmentally. The zebrafish (Danio rerio) has emerged as a particularly useful model organism tool to access neurobehavioral and drug-evoked responses. Here, we discuss recent findings and the role of the intraspecies variance in neurobehavioral, pharmacological and toxicological studies utilizing zebrafish and other fish models. We also critically evaluate common sources of intraspecies variation and outline potential strategies to improve data reproducibility and translatability.

Zebrafish breeding program: genetic parameters estimates for growth traits

The objective of this study was to evaluate the genetic parameters of two generations of zebrafish breeding program. The base population was formed by crossing individuals of six commercial stocks of zebrafish, resulting in a nucleus with 60 families. Two generations were evaluated, with a total of 780 and 781 individuals for the first and second generation, respectively. The selection was made based on the mean genetic value of each family, followed by mass selection of the breeders. Mathematical models that considered the fixed (age, density in the larval stage, sex, and generation) and random (animal additive genetics, common to full-sibs, and residual) effects were evaluated using BLUPF90 program family. Weight and total length were used as response variables. Total length was the best selection criterion because it had a higher heritability (0.30) than weight (0.22). There was a high common to full-sib effect, especially in the first generation of animals. For second-generation data, the heritability was 0.26 for total length, as well as a lower common to full-sib effect for length. The best model obtained for this evaluation was considering all effects, being age and density as first and second polynomial, respectively. The genetic and phenotypic correlations for weight and length were 0.87 and 0.75, respectively. These results indicate that genetic breeding using total length as the selection criterion may produce a larger and heavier zebrafish strain.

Characterizing sources of variability in zebrafish embryo screening protocols

There is a need for fast, efficient, and cost-effective hazard identification and characterization of chemical hazards. This need is generating increased interest in the use of zebrafish embryos as both a screening tool and an alternative to mammalian test methods. A Collaborative Workshop on Aquatic Models and 21st Century Toxicology identified the lack of appropriate and consistent testing protocols as a challenge to the broader application of the zebrafish embryo model. The National Toxicology Program established the Systematic Evaluation of the Application of Zebrafish in Toxicology (SEAZIT) initiative to address the lack of consistent testing guidelines and identify sources of variability for zebrafish-based assays. This report summarizes initial SEAZIT information-gathering efforts. Investigators in academic, government, and industry laboratories that routinely use zebrafish embryos for chemical toxicity testing were asked about their husbandry practices and standard protocols. Information was collected about protocol components including zebrafish strains, feed, system water, disease surveillance, embryo exposure conditions, and endpoints. Literature was reviewed to assess issues raised by the investigators. Interviews revealed substantial variability across design parameters, data collected, and analysis procedures. The presence of the chorion and renewal of exposure media (static versus static-renewal) were identified as design parameters that could potentially influence study outcomes and should be investigated further with studies to determine chemical uptake from treatment solution into embryos. The information gathered in this effort provides a basis for future SEAZIT activities to promote more consistent practices among researchers using zebrafish embryos for toxicity evaluation.

An Interrogation of Shared and Unique Copy Number Variants Across Genetically Distinct Zebrafish Strains

Zebrafish (Danio rerio) are a widely utilized model system for human disorders, but common laboratory strains have distinct behavioral and physiological differences. Accompanying these known strain differences, commonly used "wildtype" zebrafish strains have both shared and unique suites of single nucleotide polymorphisms and copy number variants (CNVs). Despite this, genomic variation is often ignored in study design, and the actual strain used is often not adequately reported. The goal of this study was to assess CNVs across three common laboratory strains of zebrafish-AB, Tubingen (TU), and WIK-and provide these data as a tool for the zebrafish community. Herein we identified 1351 CNV regions within the most recent genome assembly (GRCz11) covering 1.9% of the zebrafish genome (31.7 Mb). CNVs were found across all chromosomes, and 2200 genes (5121 transcripts) lie within ±5 kb of identified CNVs, pointing to likely cis regulatory actions of CNVs on nearby gene neighbors. We have created a Public Session accessible on the UCSC Genome Browser to view CNVs from this study titled "danRer11 zebrafish CNV across strains" as a tool for the zebrafish community.

Short exposure to low concentrations of alcohol during embryonic development has only subtle and strain- dependent effect on the levels of five amino acid neurotransmitters in zebrafish

The zebrafish has been successfully employed to model and study the effects of embryonic alcohol exposure. Short exposure to low alcohol concentrations during embryonic development has been shown to significantly disrupt social behavior as well as the dopaminergic and serotoninergic systems in zebrafish. However, analysis of potential effects of embryonic alcohol exposure on other amino acid neurotransmitter systems has not been performed. Here we analyzed neurochemicals obtained from adult AB and TU strain zebrafish that were immersed in 0.00% (control), 0.25%, 0.50%, 0.75% or 1.00% alcohol solution (vol/vol%) at 24 h post-fertilization for 2 h. From whole brain extracts, we quantified glutamate, aspartate, glycine, taurine and GABA levels using high performance liquid chromatography (HPLC). We found embryonic alcohol exposure not to have any significant effect on the levels of glutamate, aspartate, glycine and GABA in both AB and TU zebrafish. AB zebrafish showed a significant elevation of taurine levels, but only in the highest alcohol dose group compared to control. These results, albeit mainly negative, together with prior findings suggest that behavioral abnormalities resulting from embryonic alcohol exposure described before for AB zebrafish may primarily be due to altered dopaminergic and serotoninergic mechanisms. Furthermore, a Principal Component Analysis conducted with all neurochemicals tested in this and in our prior study, found a strain-dependent correlation structure response to embryonic alcohol treatment, confirming that embryonic alcohol effects may be genotype dependent.

A comparative examination of cortisol effects on muscle myostatin and HSP90 gene expression in salmonids

Cortisol, the primary corticosteroid in teleost fishes, is released in response to stressors to elicit local functions, however little is understood regarding muscle-specific responses to cortisol in these fishes. In mammals, glucocorticoids strongly regulate the muscle growth inhibitor, myostatin, via glucocorticoid response elements (GREs) leading to muscle atrophy. Bioinformatics methods suggest that this regulatory mechanism is conserved among vertebrates, however recent evidence suggests some fishes exhibit divergent regulation. Therefore, the aim of this study was to evaluate the conserved actions of cortisol on myostatin and hsp90 expression to determine if variations in cortisol interactions have emerged in salmonid species. Representative salmonids; Chinook salmon (Oncorhynchus tshawytscha), cutthroat trout (Oncorhynchus clarki), brook trout (Salvelinus fontinalis), and Atlantic salmon (Salmo salar); were injected intraperitoneally with a cortisol implant (50μg/g body weight) and muscle gene expression was quantified after 48h. Plasma glucose and cortisol levels were significantly elevated by cortisol in all species, demonstrating physiological effectiveness of the treatment. HSP90 mRNA levels were elevated by cortisol in brook trout, Chinook salmon, and Atlantic salmon, but were decreased in cutthroat trout. Myostatin mRNA levels were affected in a species, tissue (muscle type), and paralog specific manner. Cortisol treatment increased myostatin expression in brook trout (Salvelinus) and Atlantic salmon (Salmo), but not in Chinook salmon (Oncorhynchus) or cutthroat trout (Oncorhynchus). Interestingly, the VC alone increased myostatin mRNA expression in Chinook and Atlantic salmon, while the addition of cortisol blocked the response. Taken together, these results suggest that cortisol affects muscle-specific gene expression in species-specific manners, with unique Oncorhynchus-specific divergence observed, that are not predictive solely based upon mammalian stress responses.

Identification of Deleterious Mutations in Myostatin Gene of Rohu Carp (Labeo rohita) Using Modeling and Molecular Dynamic Simulation Approaches

The myostatin (MSTN) is a known negative growth regulator of skeletal muscle. The mutated myostatin showed a double-muscular phenotype having a positive significance for the farmed animals. Consequently, adequate information is not available in the teleosts, including farmed rohu carp, Labeo rohita. In the absence of experimental evidence, computational algorithms were utilized in predicting the impact of point mutation of rohu myostatin, especially its structural and functional relationships. The four mutations were generated at different positions (p.D76A, p.Q204P, p.C312Y, and p.D313A) of MSTN protein of rohu. The impacts of each mutant were analyzed using SIFT, I-Mutant 2.0, PANTHER, and PROVEAN, wherein two substitutions (p.D76A and p.Q204P) were predicted as deleterious. The comparative structural analysis of each mutant protein with the native was explored using 3D modeling as well as molecular-dynamic simulation techniques. The simulation showed altered dynamic behaviors concerning RMSD and RMSF, for either p.D76A or p.Q204P substitution, when compared with the native counterpart. Interestingly, incorporated two mutations imposed a significant negative impact on protein structure and stability. The present study provided the first-hand information in identifying possible amino acids, where mutations could be incorporated into MSTN gene of rohu carp including other carps for undertaking further in vivo studies.

cDNA structure and the effect of fasting on myostatin expression in walking catfish (Clarias macrocephalus, Günther 1864)

We cloned and sequenced the myostatin (MSTN) gene of walking catfish and characterized its expression under different conditions. The full cDNA sequence of MSTN was 1,784 bp, containing an open reading frame of 1,191 bp, which encoded 396 amino acids. The deduced MSTN sequence contained functional sites similar to other members of TGF-β superfamily, including the proteolytic processing site and nine conserved cysteines in the C-terminal. Walking catfish MSTN mRNA was strongly expressed in skeletal muscle and brain tissues, consistent with the expression profiles of MSTN-1 isoform in other teleosts. Temporal expression analysis revealed that the MSTN was expressed at the highest levels in 1-week-old larvae and adults, but was lowest in early juveniles. A fasting-re-feeding experiment was used to evaluate the effects of starvation on growth and MSTN expression in juvenile walking catfish for 28 days. MSTN transcript levels increased significantly (threefold) after 7 days of fasting (P < 0.05) compared with the fed control. Subsequently, MSTN expression levels decreased 1.6-fold when fasting was extended to 14 days. Although re-feeding decreased the MSTN expression relative to the levels of the fed control, the period was not long enough for growth recovery of the juveniles. Our results supported a role of MSTN as a negative regulator of muscle growth and, possibly, a role in energy conservation in fish.

The effects of exogenous cortisol on myostatin transcription in rainbow trout, Oncorhynchus mykiss

Glucocorticoids (GCs) strongly regulate myostatin expression in mammals via glucocorticoid response elements (GREs), and bioinformatics methods suggest that this regulatory mechanism is conserved among many vertebrates. However, the multiple myostatin genes found in some fishes may be an exception. In silico promoter analyses of the three putative rainbow trout (Oncorhynchus mykiss) myostatin promoters have failed to identify putative GREs, suggesting a divergence in myostatin function. Therefore, we hypothesized that myostatin mRNA expression is not regulated by glucocorticoids in rainbow trout. In this study, both juvenile rainbow trout and primary trout myoblasts were treated with cortisol to examine the effects on myostatin mRNA expression. Results suggest that exogenous cortisol does not regulate myostatin-1a and -1b expression in vivo, as myostatin mRNA levels were not significantly affected by cortisol treatment in either red or white muscle tissue. In red muscle, myostatin-2a levels were significantly elevated in the cortisol treatment group relative to the control, but not the vehicle control, at both 12 h and 24 h post-injection. As such, it is unclear if cortisol was acting alone or in combination with the vehicle. Cortisol increased myostatin-1b expression in a dose-dependent manner in vitro. Further work is needed to determine if this response is the direct result of cortisol acting on the myostatin-1b promoter or through an alternative mechanism. These results suggest that regulation of myostatin by cortisol may not be as highly conserved as previously thought and support previous work that describes potential functional divergence of the multiple myostatin genes in fishes.

Toxicity of chlorine to zebrafish embryos

Surface disinfection of fertilized fish eggs is widely used in aquaculture to reduce extraovum pathogens that may be released from brood fish during spawning, and this is routinely used in zebrafish Danio rerio research laboratories. Most laboratories use approximately 25 to 50 ppm unbuffered chlorine solution for 5 to 10 min. Treatment of embryos with chlorine has significant germicidal effects for many Gram-negative bacteria, viruses, and trophozoite stages of protozoa, but is less effective against cyst or spore stages of protozoa and certain Mycobacterium spp. Therefore, we evaluated the toxicity of unbuffered and buffered chlorine solutions to embryos exposed at 6 or 24 h post-fertilization (hpf) to determine whether higher concentrations can be used for treating zebrafish embryos. Most of our experiments entailed using an outbred line (5D), with both mortality and malformations as endpoints. We found that 6 hpf embryos consistently were more resistant than 24 hpf embryos to the toxic effects of chlorine. Chlorine is more toxic and germicidal at lower pH, and chlorine causes elevated pH. Consistent with this, we found that unbuffered chlorine solutions (pH ca. 8-9) were less toxic at corresponding concentrations than solutions buffered to pH 7. Based on our findings here, we recommend treating 6 hpf embryos for 10 min and 24 hpf embryos for 5 min with unbuffered chlorine solution at 100 ppm.

Revisiting the paradigm of myostatin in vertebrates: insights from fishes

In the last decade, myostatin (MSTN), a member of the TGFβ superfamily, has emerged as a strong inhibitor of muscle growth in mammals. In fish many studies reveal a strong conservation of mstn gene organization, sequence, and protein structures. Because of ancient genome duplication, teleostei may have retained two copies of mstn genes and even up to four copies in salmonids due to additional genome duplication event. In sharp contrast to mammals, the different fish mstn orthologs are widely expressed with a tissue-specific expression pattern. Quantification of mstn mRNA in fish under different physiological conditions, demonstrates that endogenous expression of mstn paralogs is rarely related to fish muscle growth rate. In addition, attempts to inhibit MSTN activity did not consistently enhance muscle growth as in mammals. In vitro, MSTN stimulates myotube atrophy and inhibits proliferation but not differentiation of myogenic cells as in mammals. In conclusion, given the strong mstn expression non-muscle tissues of fish, we propose a new hypothesis stating that fish MSTN functions as a general inhibitors of cell proliferation and cell growth to control tissue mass but is not specialized into a strong muscle regulator.

Strain dependent neurochemical changes induced by embryonic alcohol exposure in zebrafish

Fetal Alcohol Spectrum Disorder (FASD) is a preventable disease of the child resulting from alcohol (ethanol) consumption by pregnant women. Despite being preventable, FASD represents a prevalent problem throughout the world. Embryonic alcohol induced abnormalities in behavioral responses to social stimuli have been shown in humans and zebrafish. The neurobiological mechanisms underlying the abnormalities remain obscured. Here we start a mechanistic analysis by investigating the effect of embryonic alcohol exposure on the neurochemistry of zebrafish. The differing severity of symptoms seen in FASD may be partially due to genetic factors. To explore such genetic effects, here we analyzed two distinct zebrafish strains: AB and TU. Zebrafish were exposed to one of the following concentrations of alcohol, 0.00%, 0.25%, 0.50%, 0.75%, or 1.00% (vol/vol %) at 24 hours post-fertilization (hpf) for 2h. From whole brain extracts we analyzed the amount of neurotransmitters dopamine and serotonin and their metabolites across 4 different developmental time points: 15, 40, 70 and 102 days post-fertilization (dpf) using high performance liquid chromatography (HPLC). AB zebrafish exhibited a significant dose dependent embryonic alcohol exposure effect which increased in robustness with age. However, TU showed no such concentration effect: the levels of neurochemicals remained mainly unaltered by embryonic alcohol exposure in all age groups. We also analyzed the amount of alcohol reaching the embryo in the two strains and ruled out the possibility that TU has a more protective chorion. We conclude that the uncovered strain differences are due to genetic differences that protect TU from the deleterious effects of embryonic alcohol exposure.

Transient inactivation of myostatin induces muscle hypertrophy and overcompensatory growth in zebrafish via inactivation of the SMAD signaling pathway

Myostatin (MSTN) is the main negative regulator of muscle growth and development in vertebrates. In fish, little is known about the molecular mechanisms behind how MSTN inactivation triggers skeletal muscle enhancement, particularly regarding the signaling pathways involved in this process. Moreover, there have not been reports on the biotechnological applications of MSTN and its signal transduction. In this context, zebrafish underwent compensatory growth using fasting and refeeding trials, and MSTN activity was inactivated with dominant negative LAPD76A recombinant proteins during the refeeding period, when a rapid, compensatory muscle growth was observed. Treated fish displayed an overcompensation of growth characterized by higher muscle hypertrophy and growth performance than constantly fed, control fish. Treatment with LAPD76A recombinant proteins triggered inactivation of the SMAD signaling pathway in skeletal muscle, the main signal transduction used by MSTN to achieve its biological actions. Therefore, transient inactivation of MSTN during the compensatory growth of zebrafish led to a decrease in the SMAD signaling pathway in muscle, triggering muscle hypertrophy and finally improving growth performance, thus, zebrafish achieved an overcompensation of growth. The present study shows an attractive strategy for improving muscle growth in a fish species by mixing a classical strategy, such as compensatory growth, and a biotechnological approach, such as the use of recombinant proteins for inhibiting the biological actions of MSTN. The mix of both strategies may represent a method that could be applied in order to improve growth in commercial fish of interest for aquaculture.