Search Results (35)

Annual killifishes of the genus Nothobranchius live in seasonal water bodies in Eastern Africa. Adults die at the end of the rainy season when seasonal pools desiccate but diapaused embryos persist in the sediments and hatch in subsequent rainy seasons. Embryos use environmental cues to determine optimal hatching conditions to begin a new generation. We simulated a predation event by crushing Nothobranchius embryos and tested if embryos of N. eggersi and N. foerschi adjust time of hatching in response to these chemical cues. We placed individual diapause III embryos in cups of dechlorinated water dosed with either (1) blank water, (2) odor of crushed chironomids, or (3) odor of crushed Nothobranchius embryos. Although N. eggersi Red embryos hatched at a significantly faster rate than embryos from N. eggersi Solid blue or N. foerschi, the effect of the cue was consistent for all three types of Nothobranchius embryos used in this study. The odor of crushed Nothobranchius embryos caused a significant delay in time to hatch relative to the two control treatments. These data suggest that Nothobranchius embryos attend to chemical alarm cues derived from crushed conspecific embryos and delay hatching as a bet-hedging strategy to avoid hatching when they detect risk of predation. Full article

Background/Aims: The Mediterranean killifish, Aphanius fasciatus (Valenciennes, 1821), is a small euryhaline and eurytherm cyprinodont. While its ecology and role as a bioindicator are well known, its anatomy remains poorly understood. This study aimed to provide the first detailed description of the digestive tract of A. fasciatus, from the oropharyngeal cavity to the rectum. Methods: An anatomical and morphological approach supported by light microscopy was applied to examine oral, pharyngeal, and intestinal structures in adult specimens. Results: The jaws bear tricuspids incisiform teeth, whereas the pharynx has caniniform teeth. The tongue forms a muscular thickening of the oral floor and aids swallowing. The oropharyngeal tract and esophagus lead to a dilated anterior intestinal region resembling a primitive stomach, with mucosal folds and mucus-secreting epithelium, but lacking gastric glands. This chamber functions mainly for food storage, absorption, and preparation rather than true gastric digestion. The intestine extends to the rectum, showing sexual dimorphism: females have a relaxed anus, males a more toned and folded structure. Conclusions: These findings provide essential baseline information for comparison with other experimental models and reinforce the suitability of A. fasciatus as a reliable model for anatomical and functional studies. Full article

Invasive fish species are a major driver of freshwater native fish biodiversity loss and their spread and impacts on the native fish are expected to increase within the current freshwater salinization and global warming crisis. In the current study, the upper thermal and salinity tolerance of the geographically range-restricted, threatened killifish Valencia robertae and its alien competitor, the globally invasive Eastern mosquitofish Gambusia holbrooki are compared in an experimental setting. Fish were exposed, after acclimation, to a continuous, dynamic temperature or salinity increase until predefined sub-lethal end points (loss of equilibrium and/or loss of buoyancy). The critical thermal and salinity maxima (CTMax and CSMax) were then calculated as the arithmetic mean of the combined thermal or salinity points at which the endpoint was attained. Finally, thermal and salinity safety margins for the two species were also calculated using abiotic data. Mosquitofish (females and males pooled) showed an average CΤmax of 35.85 °C and the killifish 36.27 °C (sexes pooled). Mosquitofish (male) showed an average CSmax of 40.25‰ and (male) killifish 42.64‰ (sexes also pooled). Killifish safety margins are much higher than those of the mosquitofish. Future impacts of global warming and salinisation on these species and on their interactions under current climate change scenarios are discussed. Full article

The Atlantic Forest coastal tablelands is home to a wide diversity of small-sized freshwater fish sharing a biogeographically congruent distributional pattern. The annual killifish Xenurolebias are among these remarkable inhabitants in the riparian wetlands with four species in the area. Xenurolebias pataxo are located between the Jucuruçu and Mucuri rivers, geographically replaced by Xenurolebias myersi at the Riacho Doce and the Rio Itaúnas, and, further south, Xenurolebias cricarensis are in the floodplains of the Rio São Mateus and Xenurolebias izecksohni, living in temporary environments of the Rio Barra Seca, north of the Rio Doce. Due to their restricted habitat in the lowlands, these annual killifish could all be designated as a target species, providing benefits in the conservation of riparian wetlands. However, less is known about their habits and real distribution. Otherwise, the accelerated habitat loss is worrisome. Two of these species are threatened with extinction on Red Lists; one is Near-Threatened; and one is Data-Deficient. After ten years since the last species description, our investigations revealed a fifth species, the first recorded south of Rio Doce. The present contribution aims to characterize the occupied habitat by each species within the temporary environments and present an updated distributional data on these fish. Additionally, a new Xenurolebias is described, the first one recorded south of Rio Doce. Full article

The African turquoise killifish is a short-lived vertebrate that is gaining interest as a model for understanding degenerative processes associated with aging, including neurodegeneration. However, due to its relatively recent adoption in laboratory research, detailed studies on the adult neuroanatomy of the killifish, particularly regarding the organization of neurotransmitter systems and their age-related changes, remain limited. Here, we study the organization of serotonergic cell populations in the brain and spinal cord of juvenile/young adult (1–3-months-old) and geriatric (5–6-months-old) killifish using anti-serotonin immunofluorescence. Our findings reveal that the overall organization of serotonergic cell populations in killifish closely resembles that of most teleosts, including pineal, pretectal, hypothalamic, rapheal and spinal cord neuronal populations. Of note, adult killifish also present a population of serotonergic neurons in the dorsolateral isthmus, which has been only described in a few other fish species. Aged killifish showed a similar organization of serotonergic cell populations to that of juveniles/young adults, with the major difference being the loss of serotonin immunoreactivity in pretectal cells of 6-month-old fish. Our study provides a neuroanatomical framework for future investigations into the serotonergic system in this emerging vertebrate model of aging. Full article

Freshwater ecosystems are increasingly stressed by drought and anthropogenic inputs that can increase specific conductivity (SPC) and pH; however, little is known about how harsher conditions affect fish. We evaluated how fish growth and diet composition changed along a natural gradient in SPC and pH in Wyoming, USA using Northern plains killifish (Fundulus kansae) and Fathead minnows (Pimephales promelas). We surveyed 201 sites where we measured water chemistry, sampled fish, and assessed invertebrate prey availability from May to September 2024. Northern plains killifish and/or Fathead minnows inhabited 12 sites, which were the focus of our study. We measured otoliths to assess growth and stomach contents to estimate dietary selectivity. Growth decreased at higher SPC (486–23,500 µS/cm) for Fathead minnows and pH (7.2–9.0) for both species, suggesting an energy trade-off with osmoregulation. Dietary analyses revealed variable selection for Chironomidae larvae, while other taxa such as Gammaridae and Coleoptera were avoided at higher SPC and pH. Despite the extreme conditions, these fish maintained some dietary preference, highlighting behavioral plasticity. Our findings suggest that while these species can tolerate harsh environments, sublethal effects on growth and diet may limit long-term fitness. This research offers a framework for assessing the viability of fish populations inhabiting ecosystems with increasing salinity and pH that can inform conservation and management strategies under future environmental change. Full article

Diapause is a state of developmental and metabolic dormancy that precedes exposure to environmental stresses. Yet, diapausing embryos are typically stress-tolerant. Evidence suggests that diapausing embryos “prepare” for stress as part of a gene expression program as they enter dormancy. Here, we investigate if diapause II embryos of the annual killifish Austrofundulus limnaeus, which can survive for hundreds of days of anoxia, can mount a transcriptomic response to anoxic insult. Bulk RNAseq was used to characterize the transcriptomes of diapause II embryos exposed to normoxia, 4 h and 24 h anoxia, and 2 h and 24 h normoxic recovery from anoxia. Differential expression and gene ontology analyses were used to probe for pathways that may mitigate survival. Transcriptional factor analysis was used to predict potential mediators of this response. Diapausing embryos exhibited a robust transcriptomic response to anoxia and recovery that returns to near baseline conditions after 24 h. Anoxia induced an upregulation of genes involved in the integrated stress response, lipid metabolism, p38mapk kinase signaling, and apoptosis. Developmental and mitochondrial genes decreased. We conclude that diapause II embryos mount a robust transcriptomic stress response when faced with anoxic insult. This response is consistent with mediating expected challenges to cellular homeostasis in anoxia. Full article

Mitochondrial oxidative phosphorylation (OXPHOS) genes are a system subject to selection under determined environmental constraints despite a neutral evolution model that has long been hypothesized for the mitochondrial genome. In this study, the sequences of ND1, Cytb, and COI OXPHOS genes were analyzed in six populations of the eurythermal and euryhaline killifish A. fasciatus, to detect non-synonymous mutations leading to amino acid changes and to check whether selection acted on them using tests of recombination and selection. The results indicate a high COI and Cytb gene diversity and a high percentage of private haplotypes in all populations. In the Greek population, non-synonymous nucleotide substitutions were observed in the N-terminal region of COI and Cytb. Positively selected sites were also found. The information we obtained from the mitochondrial DNA sequences of A. fasciatus adds to the growing data on selective pressure acting on mitochondrial DNA in non-model species. These results should be explored from the perspective of the local adaptation of eurythermal and euryhaline species and supported using experimental evidence to better understand the interplay between historical climatic events and local adaptation and how each of them contributes to shaping the genetic structure of this species. Full article

Specific subpopulations of neurons in nerve and sensory systems must be developed and maintained, and this is accomplished in significant part by neurotrophins (NTs) and the signaling receptors on which they act, called tyrosine protein kinase receptors (Trks). The neurotrophins–tyrosine protein kinase receptors (NTs/Trks) system is involved in sensory organ regulation, including the visual system. An NTs/Trks system alteration is associated with neurodegeneration related to aging and diseases, including retinal pathologies. An emergent model in the field of translational medicine, for instance, in aging study, is the annual killifish belonging to the Nothobranchius genus, thanks to its short lifespan. Members of this genus, such as Nothobranchius guentheri, and humans share a similar retinal stratigraphy. Nevertheless, according to the authors’ knowledge, the occurrence and distribution of the NTs/Trks system in the retina of N. guentheri has never been investigated before. Therefore, the present study aimed to localize neurotrophin BDNF, NGF, and NT-3 and TrkA, TrkB, and TrkC receptors in the N. guentheri retina using the immunofluorescence method. The present investigation demonstrates, for the first time, the occurrence of the NTs/Trks system in N. guentheri retina and, consequently, the potential key role of these proteins in the biology and survival of the retinal cells. Full article

Calcium-binding proteins (CaBPs) are members of a heterogeneous family of proteins able to buffer intracellular Ca²⁺ ion concentration. CaBPs are expressed in the central and peripheral nervous system, including a subpopulation of retinal neurons. Since neurons expressing different CaBPs show different susceptibility to degeneration, it could be hypothesized that they are not just markers of different neuronal subpopulations, but that they might be crucial in survival. CaBPs’ ability to buffer Ca²⁺ cytoplasmatic concentration makes them able to defend against a toxic increase in intracellular calcium that can lead to neurodegenerative processes, including those related to aging. An emergent model for aging studies is the annual killifish belonging to the Nothobranchius genus, thanks to its short lifespan. Members of this genus, such as Nothobranchius guentheri, show a retinal stratigraphy similar to that of other actinopterygian fishes and humans. However, according to our knowledge, CaBPs’ occurrence and distribution in the retina of N. guentheri have never been investigated before. Therefore, the present study aimed to localize Calretinin N-18, Parvalbumin, and S100 protein (S100p) in the N. guentheri retina with immunohistochemistry methods. The results of the present investigation demonstrate for the first time the occurrence of Calretinin N-18, Parvalbumin, and S100p in N. guentheri retina and, consequently, the potential key role of these CaBPs in the biology of the retinal cells. Hence, the suitability of N. guentheri as a model to study the changes in CaBPs’ expression patterns during neurodegenerative processes affecting the retina related both to disease and aging can be assumed. Full article

Transitional waters are fragile ecosystems with high ecological values, representing the breeding and resting sites for rare and threatened species. They warrant particular attention in regards to protection, as they experience numerous anthropogenic threats. The present review aims to analyze the recent literature on Aphanius fasciatus, currently considered one of the most strictly estuarine-dependent fish species, thus affected by the degradation of lagoon habitats, and to discuss its suitability as a sentinel species for protection of the quality of transitional water environments. The analysis and discussion highlight the potential applicability of the molecular, cellular, and physiological responses of this species as diagnostic tools for detecting the subtle effects induced by environmental pollution on the biota in transitional water environments. Moreover, the suitability of the responses of this species is suggested in the wider framework of the One Health perspective, which considers human and animal health and the environmental state to be highly interconnected, sharing common aspects. To date, omics technologies show great potential in reacquiring novel knowledge on the responses of the organisms to environmental changes and to the alterations of the environmental health status. Therefore, considering the relevant potential of this organism as a sentinel species, many efforts are required in the near future to improve the quantity and quality of the omics tools that refer to A. fasciatus. Full article

Coastal wetlands worldwide are experiencing high rates of loss and degradation that may lead to a reduction in diversity in faunal populations. Since salt marsh habitats are subject to a multitude of stressors, evaluations of the genetic diversity, connectivity, and potential resilience of faunal communities within salt marsh habitats are relevant. This study characterizes mitochondrial DNA (mtDNA) diversity for three common faunal residents of salt marshes along the northern Gulf of Mexico. Gulf Killifish (Fundulus grandis) samples were characterized for 1077 bp of the concatenated nucleotide sequence corresponding to the Control Region and Nitrogen Dehydrogenase, Subunits 2 and 5. Daggerblade grass shrimp (Palaemon pugio) samples were characterized using 466 bp of 16sRNA sequence, and phloem-feeding planthoppers (Prokelisia marginata) were characterized using 372 bp of Cytochrome c Oxidase Subunit I (COI) sequence. For F. grandis, our data revealed high levels of haplotypic diversity, evidence of isolation by distance (IBD), and regional population structuring associated with the distribution of two distinct phylogroups and distinct historical demography signatures. P. pugio and P. marginata displayed low levels of haplotypic diversity and evidence of population structure, but both appear to contain only snapshots of the total potential diversity for these species in the Gulf of Mexico. Greater resolution of the patterns of historical demography of Gulf Killifish may be obtained in future studies by including localities from Florida and Mexico. For both P. pugio and planthoppers, future studies would benefit from the characterization of genetic markers with a higher degree of polymorphism. We conclude that despite these three species inhabiting the same habitats along the same stretch of coast, each is subject to a different combination of evolutionary forces, and this study was able to reconstruct differences in how the genetic variation in each of these species emerged, and how it is maintained. Full article

Neurodegenerative disorders are characterized by the progressive loss of neuronal structure or function, resulting in memory loss and movement disorders. Although the detailed pathogenic mechanism has not been elucidated, it is thought to be related to the loss of mitochondrial function in the process of aging. Animal models that mimic the pathology of a disease are essential for understanding human diseases. In recent years, small fish have become ideal vertebrate models for human disease due to their high genetic and histological homology to humans, ease of in vivo imaging, and ease of genetic manipulation. In this review, we first outline the impact of mitochondrial dysfunction on the progression of neurodegenerative diseases. Then, we highlight the advantages of small fish as model organisms, and present examples of previous studies regarding mitochondria-related neuronal disorders. Lastly, we discuss the applicability of the turquoise killifish, a unique model for aging research, as a model for neurodegenerative diseases. Small fish models are expected to advance our understanding of the mitochondrial function in vivo, the pathogenesis of neurodegenerative diseases, and be important tools for developing therapies to treat diseases. Full article

The annual turquoise killifish (Nothobranchius furzeri) is a laboratory model organism for neuroscience of aging. In the present study, we investigated for the first time the levels of serotonin and its main metabolite, 5-hydroxyindoleacetic acid, as well as the activities of the key enzymes of its synthesis, tryptophan hydroxylases, and degradation, monoamine oxidase, in the brains of 2-, 4- and 7-month-old male and female N. furzeri. The marked effect of age on the body mass and the level of serotonin, as well as the activities of tryptophan hydroxylases and monoamine oxidase in the brain of killifish were revealed. The level of serotonin decreased in the brain of 7-month-old males and females compared with 2-month-old ones. A significant decrease in the tryptophan hydroxylase activity and an increase in the monoamine oxidase activity in the brain of 7-month-old females compared to 2-month-old females was shown. These findings agree with the age-related alterations in expression of the genes encoding tryptophan hydroxylases and monoamine oxidase. N. furzeri is a suitable model with which to study the fundamental problems of age-related changes of the serotonin system in the brain. Full article

Although there is rising global concern over the environmental, ecological, and human health risks associated with the discharge of leachates from e-waste dumpsites into the aquatic ecosystems, little is known in this research area. Thus, for this study, we first defined the chemistry of the test leachate, followed by assessment of the leachate on the development of a model aquatic organism (Fundulus heteroclitus) used extensively as a bioassay organism in pollution studies. Chemical analyses revealed that levels of phosphate (20.03 mg/L), cadmium (Cd) (0.4 mg/L), lead (Pb) (0.2 mg/L), and chromium (Cr) (0.4 mg/L) were higher than the 2009 US EPA and the 2009 National Environmental Standards and Regulations Enforcement Agency (NESREA) permissible limits. Polycyclic aromatic hydrocarbon (PAH) burdens were dominated mainly by the high molecular weight congeners, specifically the ∑4rings (73 µg/L). Total polychlorinated biphenyls (PCB) levels ranged from 0.00 to 0.40 µg/L with the ∑deca PCBs reaching the highest concentration. For the biological studies, F. heteroclitus embryos (48-h post-fertilization) were divided randomly into groups and exposed to one of six e-waste leachate concentrations (10, 1, 0.1, 0.01, 0.001, 0.0001%). Significant differences (p ≤ 0.05) between treated and control groups were observed in standard and total length, and head size. Further analysis using Duncan’s post-hoc test of multiple comparison also revealed specific differences within and between specific treatment groups. We conclude that e-waste leachate arising from indiscriminate dumping into aquatic ecosystems in Nigeria contains mixtures of toxic constituents that can threaten ecosystem and public health. Full article