Fish Brain Research Articles

Hiostopathological studies on gill, liver and brain of oreochromis mossambicus exposed to ethoxyquin

Water pollution greatly affects the life of aquatic ecosystem. Ethoxyquin (EQ) is one such toxic content, which is even present in the food being presented to the aquatic beings. In this research work, the effects of ethoxyquin on the Oreochromis mossambicus, called tilapia fish is studied. The aimed fish species is treated through the sublethal concentration of EQ. The effects of this toxic content on the aspects histopathological parameters were studied and the results were presented. Histopathological analysis was attempted on the gill, liver and brain of the tilapia fish taken up for the study. The histological abnormalities that were seen were curling of secondary lamella, which was followed by disorder and rupture in the secondary lamellae. These changes were more widespread and more apparent in the gills and liver of the Oreochromis mossambicus. A haemorrhage at the main lamellae and a swelling at the primary filament's tip were also seen during the examination. Analysis of the brain, inferred that no severe damages to the neurons are reported. As a conclusion, the results of the current histology examinations reveal that the EQ exposure caused moderate to severe damage to the gills and liver of the O. Mossambicus, whereas only moderate damage to the brain neurons.

Effects of 17α-Methyltestosterone on the Transcriptome and Sex Hormones in the Brain of Gobiocypris rarus

17α-Methyltestosterone (MT), a synthetic environmental endocrine disruptor with androgenic effects, has been shown to disrupt the reproductive system and inhibit germ cell maturation in Gobiocypris rarus. To further investigate the regulation of gonadal development by MT through the hypothalamic-pituitary-gonadal (HPG) axis, G. rarus were exposed to 0, 25, 50, and 100 ng/L of MT for 7, 14, and 21 days. We analyzed its biological indicators, gonadotropin-releasing hormone (GnRH), gonadotropins, reproduction-related gene expression, and brain tissue transcriptome profiles. We found a significant decrease in the gonadosomatic index (GSI) in G. rarus males exposed to MT for 21 days compared to the control group. GnRH, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) levels, as well as the expressions of the gnrh3, gnrhr1, gnrhr3, fshβ, and cyp19a1b genes, were significantly reduced in the brains of both male and female fish when exposed to 100 ng/L MT for 14 days compared to the controls. Therefore, we further constructed four RNA-seq libraries from 100 ng/L MT-treated groups of male and female fish, obtaining 2412 and 2509 DEGs in male and female brain tissue, respectively. Three common pathways were observed to be affected in both sexes after exposure to MT, namely, nicotinate and nicotinamide metabolism, focal adhesion, and cell adhesion molecules. Furthermore, we found that MT affected the PI3K/Akt/FoxO3a signaling pathway through the upregulation of foxo3 and ccnd2, and the downregulation of pik3c3 and ccnd1. Therefore, we hypothesize that MT interferes with the levels of gonadotropin-releasing hormone (GnRH, FSH, and LH) in G. rarus brains through the PI3K/Akt/FoxO3a signaling pathway, and affects the expression of key genes in the hormone production pathway (gnrh3, gnrhr1 and cyp19a1b) to interfere with the stability of the HPG axis, thus leading to abnormal gonadal development. This study provides a multidimensional perspective on the damaging effects of MT on fish and confirms that G. rarus is a suitable model animal for aquatic toxicology.

Removal of lithium from aqueous solutions by solid-phase extraction using sawdust loaded with magnetite nanoparticles and study of apoptosis, MDA and 8-OHdG caused by lithium toxicity in fish brain.

Lithium, which has a high industrial value, is an environmental pollutant of concern to those who work with lithium in industry as well as to the general public. Biological parameters such as MDA, 8-OHdG, apoptosis (caspase-3), and acetylcholinesterase (AChE) were studied to determine the toxic effects on the brain tissue of the model organism (Carassius auratus) exposed to high dose lithium. According to the results obtained, it was found that lithium exposure caused oxidative stress with an increase in MDA level over time and, accordingly, DNA damage and apoptosis occured in brain tissue. It was also found that a decrease in AChE activity was observed, and the high levels of MDA, 8-OHdG, and caspase-3 activity obtained in brain tissue supported this result. The solid phase extraction (SPE) method was used to effectively remove lithium, which has unfavorable effects on living organisms, from aqueous solutions. In this method, a sawdust loaded with magnetite nanoparticles (MNLS) was prepared as an adsorbent for solid phase extraction by a simple method, and it was characterized. Optimal conditions for the SPE process were defined and it was found that lithium could be removed from solution onto the MNLS surface with a high yield of about 96%. The results of the study are crucial for proposing a simple and applicable high performance method.

Evaluation of a chronic exposure to nanoplastics in goldfish (Carassius auratus): Analytical validation of automated assays for the measurement of biochemical markers

The bulk of plastic pollution is mainly composed of small fragments, micro- and nanoplastics (NPs). Although many studies are currently published on NPs, research on the effects of NPs in fish after a chronic exposure is still scarce. The present study aimed to validate a series of automated assays to be used in the monitoring of fish challenged with a chronic exposure to NPs, using Carassius auratus (goldfish) as model species. For this purpose, adult C. auratus were exposed to 100 µg/L polystyrene (PS)-NPs for a 30-day period. Total oxidative status (TOS), total antioxidant capacity (TAC), esterase activity (EA) and adenosine deaminase activity (ADA) were measured in the gills, brain and muscle of fish. In addition, acetylcholinesterase activity (AChE) and creatinine kinase (CK) were measured in the muscle. All biomarkers were successfully validated in goldfish tissues and consequently used to assess the effects of NPs following a chronic exposure. Results showed that EA and TAC significantly increased in gills, while EA decreased significantly in the brain, and no effects were observed in any of these parameters in muscle. These results indicate that both immune and antioxidant responses were triggered by NPs in gills, but not in the brain nor muscle. This suggests that gills may be a primary target for NPs, potentially leading to a cascading effect on gas exchange, or osmo- and ionic regulation that should be further investigated.

Exceptional fossil preservation and evolution of the ray-finned fish brain.

Brain anatomy provides key evidence for the relationships between ray-finned fishes1, but two majorlimitations obscure our understanding of neuroanatomical evolution in this major vertebrate group. First, the deepest branching living lineages are separated from the group's common ancestor by hundreds of millions of years, with indications that aspects of their brain morphology-like other aspects of their anatomy2,3-are specialized relative to primitive conditions. Second, there are no direct constraints on brain morphology in the earliest ray-finned fishes beyond the coarse picture provided by cranial endocasts: natural or virtual infillings of void spaces within the skull4-8. Here we report brain and cranial nerve soft-tissue preservation in Coccocephalus wildi, an approximately 319-million-year-old ray-finned fish. This example of a well-preserved vertebrate brain provides a window into neural anatomy deep within ray-finned fish phylogeny. Coccocephalus indicates a more complicated pattern of brain evolution than suggested by living species alone, highlighting cladistian apomorphies1 and providing temporal constraints on the origin of traits uniting all extant ray-finned fishes1,9. Our findings, along with a growing set of studies in other animal groups10-12, point to the importance of ancient soft tissue preservation in understanding the deep evolutionary assembly of major anatomical systems outside of the narrow subset of skeletal tissues13-15.

Isolation, Characterization, and Transcriptome Analysis of an ISKNV-Like Virus from Largemouth Bass.

Largemouth bass (Micropterus salmoides) is an important commercial fish farmed in China. Challenges related to diseases caused by pathogens, such as iridovirus, have become increasingly serious. In 2017, we detected iridovirus-infected diseased largemouth bass in Zunyi, Guizhou Province. The isolated virus was identified as an infectious spleen and kidney necrosis virus (ISKNV)-like virus (ISKNV-ZY). ISKNV-ZY induces a cytopathic effect after infecting mandarin fish brain (MFB) cells. Abundant hexagonal virus particles were observed in the cytoplasm of ISKNV-ZY-infected MFB cells, using electron microscopy. The whole genome of ISKNV-ZY contained 112,248 bp and 122 open reading frames. Phylogenetic tree analysis showed that ISKNV-ZY was most closely related to BCIV, indicating that it is an ISKNV-like megalocytivirus. ISKNV-ZY-infected largemouth bass started to die on day six and reached a death peak on days 7-8. Cumulative mortality reached 100% on day 10. Using RNA sequencing-based transcriptome analysis after ISKNV-ZY infection, 6254 differentially expressed unigenes (DEGs) were identified, of which 3518 were upregulated and 2673 downregulated. The DEGs were associated with endocytosis, thermogenesis, oxidative phosphorylation, the JAK-STAT signaling pathway, the MAPK signaling pathway, etc. These results contribute to understanding the molecular regulation mechanism of ISKNV infection and provide a basis for ISKNV prevention.

Acute Toxicity, and Neurobehavioural Responses of Afidopyropen on Exposure to Freshwater Edible Fish, Cyprinus carpio (Linnaeus)

Nowadays water pollution has become a real concerning problem worldwide in the aquatic ecosystem, due to the increasing use of a variety of pesticides in agriculture for the growing food demand in the world. Thereby in this investigation, we examined the LC50 value of afidopyropen, an insecticide, in addition to selected behavioural and ACh, AChE activity of Cyprinus carpio fingerlings. Fingerlings were exposed to different concentrations of afidopyropen ranging from 0.4mg to 1.6 mg/L by the semi-static bioassay method. And it had been found to be 1.0 mg/L. The fish exposed to this insecticide showed remarkable behavioural abnormalities in a dose-dependent manner. ACh accumulation and AChE inhibition in carp (Cyprinus carpio) exposed to a different concentration for the period of 96 hrs caused a significant increase in the elevation of acetylcholine (ACh), and was related to a marked decrease in the activity of acetylcholinesterase (AChE). In comparison with the corresponding controls, AChE activity was significantly decreased, whereas the ACh accumulation was markedly elevated due to the interaction of AChE activity which remarks in excess accumulation of acetylcholine at the neuromuscular junctions and synapses leading to make them more excitable for the behavioural changes due to impaired neurophysiology of the fish brain. The toxicity of afidopyropen during exposure to fish suggests that this compound poses a greater risk to fish.

Effects of essential oil of Magnolia denudata on spotted seabass (Lateolabrax maculatus) during simulated live transportation

The essential oil of Magnolia denudate (MDO) is an effective anesthetic and sedative on spotted seabass (Lateolabrax maculatus). To improve animal welfare and transportation effectiveness, this study evaluated the effects of MDO on water quality, blood biochemical, and tissue damage after the transportation of L. maculatus (164.16 ± 15.40 g). A base group (no MDO and no transport) and 0 (control group), 10, and 20 mg/L MDO during simulated transportation treatments of 5 h were involved. Every treatment has four replicates with four fish transported in a plastic box (34 × 22.5 × 19 cm) with 5 L water at a fish density of 130 g/L and a shake rate of 60 rpm. At the end of the transportation simulation, no mortality was observed. Fish were immediately sampled for blood collection, liver and brain removal. Compared to the control group, the MDO groups showed significantly lower ammonia in water, lower cortisol level and lactic dehydrogenase activity, higher glucose, aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase activities in fish serum (p < 0.05). Superoxide dismutase (SOD), catalase (CAT) activity, glutathione (GSH) concentration decline, and malondialdehyde (MDA) were alleviated in the fish brain when MDO was added to the water. However, SOD and GSH further decreased, but MDA increased in the fish liver in the MDO groups (p < 0.05). These results revealed that the administration of MDO on L. maculatus transportation could alleviate stress and decrease energy metabolism. Due to the 20 mg/L MDO may trigger more serve liver function decline, we suggest 10 mg/L MDO addition in L. maculatus transportation.

Neuroprotective properties of borax against aluminum hydroxide-induced neurotoxicity: Possible role of Nrf-2/BDNF/AChE pathways in fish brain

The current study was designed to assess the possible neuroprotective effect of borax (BX) against the toxicity of aluminum hydroxide [AH, Al (OH)3] on brain of rainbow trout (Oncorhynchus mykiss) with multibiomarker approaches. For this purpose, the presence of the neuroprotective action by BX against the AH exposure was assessed by the activities of catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), myeloperoxidase (MPO), acetylcholinesterase (AChE). In addition, we evaluated glutathione (GSH), malondialdehyde (MDA), DNA damage (8-OHdG), apoptosis (caspase 3), tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), nuclear factor erythroid-2 (Nrf-2), and brain-derived neurotrophic factor (BDNF) levels in 96 h semi-static treatment. In the 48th and 96th hour samplings, apoptosis induced by AH in the Nrf-2/BDNF/AChE pathways in rainbow trout brain tissue was revealed by DNA damage, enzyme inhibitions and lipid peroxidations. On the contrary applications of BX supported antioxidant capacity without leading apoptosis, lipid peroxidation, inflammatory response and DNA damage. BX also increased the BDNF levels and AChE activity. Moreover, BX exerted a neuroprotective effect against AH-induced neurotoxicity via down-regulating cytokine-related pathways, minimising DNA damage, apoptosis as well as up-regulating GSH, AChE, BDNF and antioxidant enzyme levels. It can be concluded that the combination of borax with AH modulated the toxic effects of AH.

Linking chemical exposure and fish metabolome: Discovering new biomarkers of environmental exposure of Argyrosomus regius to the antidepressant venlafaxine

In this study, a non-target metabolomic approach was used to investigate changes in the metabolome of juvenile meagre (Argyrosomus regius) exposed to venlafaxine (20 µg/L). A total of 24, 22 and 8 endogenous metabolites tentatively identified in liver, brain and plasma, respectively, were significantly changed in venlafaxine exposed meagre, showing tissue-dependent variations in the metabolic profile. The amino acids tryptophan, tyrosine and phenylalanine, which are related to the synthesis, availability, and expression of neurotransmitters (e.g., serotonin, dopamine, epinephrine), showed to be dysregulated by venlafaxine exposure. A high impact was observed in fish brain metabolome that showed a trend of up-regulation for most of the tentatively identified metabolites. In conclusion, the identification of possible biomarkers of exposure in fish metabolome to environmental stressors such as venlafaxine is crucial to assess early signal changes at molecular level, enabling the prevention of deleterious effects at the organism and population levels.

Effects of LED spectrum on circadian rhythmic expression of clock genes and Aanat2 in the brain of juvenile European seabass (Dicentrarchus labrax)

The circadian rhythm is a physiological phenomenon that occurs in various organisms with a cycle of about 24 hours. Light is one of the important environmental factors affecting biological rhythm. To clarify whether a shift in light spectrum can influence the circadian expression in fish brain, a total of 175 European seabasses [body weight: 32.5 ± 0.71) g; body length: (13.78 ± 0.35) cm] were exposed to white light (WL), red light (RL), yellow light (YL), green light (GL) or blue light (BL). After 50 days of exposure, circadian expressions of four core clock genes (Clock, Bmal1, Per2, Cry1) and Aanat2 gene in brain were examined. The results showed that the temporal expression patterns of positive clock gens (Clock and Bmal1) showed increases during the scotophase and decreases during the photophase, with peaks near the middle of the darkness. Clock gene expression showed a stable circadian rhythm (R2 = 0.578-0.824, P=0.000- 0.027) in all light groups while Bmal1 showed circadian rhythm in WL, GL and RL, not in BL and YL. Daily expression patterns of the negative clock genes oscillated in the opposite phase from the positive clock genes, showing increasing mRNA levels during the light, decreases during the dark, and peaks near the shift from night to day, except Per2 in RL and Cry1 in BL. Compared with WL, the acrophases of Clock and Bmal1 were delayed under all light treatments (BL: + 3.7h, +6.73h; RL: +2.4h,+1.35h; YL: + 4.94h, 2.00h; GL: +0.05, +0.16h). Cry1 showed advanced acrophase under all light treatments (BL: -10.74 h, GL: -3.81 h, RL: -3.93 h, YL: -7.56 h) but Per2 showed delayed acrophase in all light treatments (GL: +0.86 h, RL: +10.35 h, YL: +9.62 h), except in BL (-0.43 h). The acrophase of Aanat2 was advanced by all monochromatic light, the Aanat2 level was significantly increased in RL compared with other light treatment. Therefore, the results indicate that RL may regulate the expression of Aanat2 gene by affecting the expression of clock gene in fish brain. Spectrum can affect the biological clock system of fish, and unreasonable spectrum may disturb the rhythm of gene expression of biological clock of fish. Under the irradiation of light spectrum, some clock genes still maintain obvious circadian oscillation, while the rhythm of some clock genes is not obvious and may be destroyed. Our findings suggest a primary role of light spectrum information to the fish brain circadian system.

Neuroendocrine regulation of reproduction by GnRH neurons: multidisciplinary studies using a small fish brain model.

After the discovery of GnRH, GnRH neurons have been considered to represent the final common pathway for the neural control of reproduction. There is now compelling data in mammals that two populations of kisspeptin neurons constitute two different systems to control the episodic and surge release of GnRH/LH for the control of different aspects of reproduction, follicular development and ovulation. However, accumulating evidence indicates that kisspeptin neurons in non-mammalian species do not serve as a regulator of reproduction, and the non-mammalian species are believed to show only surge release of GnRH to trigger ovulation. Therefore, the GnRH neurons in non-mammalian species may offer simpler models for the study of their functions in neuroendocrine regulation of reproduction, especially ovulation. Our research group has taken advantage of many unique technical advantages of small fish brain for the study of anatomy and physiology of GnRH neurons, which underly regular ovulatory cycles during the breeding season. Here, recent advances in multidisciplinary study of GnRH neurons are reviewed, with a focus on studies using small teleost fish models.

EFFECT OF SUB-LETHAL CONCENTRATION OF NICOTINE IN SURFACE WATERS ON ENZYMATICAL CHANGES IN TISSUES OF Labeo rohita FINGERLINGS

The current study aims to analyse the impact of the sub-lethal concentration of nicotine in surface waters on enzymatical changes in tissues of Labeo rohita fingerlings. The experimental fish Labeo rohita fingerlings were exposed to sub-lethal nicotine concentrations in surface water (0.93 mgL-1) for 60 days. Tissues (liver, gill and kidney) were harvested at different intervals (15, 30, 45 and 60 days of nicotine exposure) to analyze metabolic enzymes, TBARS and antioxidant enzymes. Further acetylcholinesterase enzyme activity was examined in the brain tissue. The metabolic enzymes such as AST and ALT activities increased significantly (p&lt;0.05). In contrast, ACP and ALP activities declined in nicotine-exposed fish of liver, gill and kidney at every interval than in control fish. The peroxidation marker TBARS activity was significantly reduced, meanwhile the activities of enzymatic antioxidants such as SOD, CAT and GPx and non-enzymatic antioxidant GSH activities declined considerably in sub-lethal concentration nicotine-exposed fish tissues (liver, gill and kidney) when compared to control fish. Further, the activity of AChE also declined in the brain of nicotine-exposed fish than in control fish. The results indicate that exposure to the sub-lethal concentration of nicotine in surface water can cause an imbalance in the activities of metabolic enzymes, TBARS, antioxidant enzymes and AChE in fish.

Cytoarchitecture of Mudskipper (Boleophthalmus pectinirostris) Brain

Mudskippers are intertidal burrowing fish with unique living habits. So far, studies on the cytoarchitecture of the brain in fish with such behaviors remain limited. Therefore, documenting the neuroanatomy of this animal is of interest because of its unique characteristics. In this study, we examined the cytoarchitecture of mudskipper (Boleophthalmus pectinirostris) brain and investigated whether it has any peculiarities in its brain structures. In general, the basic composition, morphology, and organization of mudskipper brain do not vary markedly from those of other teleosts. The main differences appear in the telencephalon and diencephalon. In addition to Nissl staining, immunostainings for catecholaminergic and cholinergic systems were performed to help identify certain nuclei. The results showed that the number of subdivisions of the central division of pallium, lateral division of pallium, and medial division of pallium were different with other teleost species. In addition, some diencephalic nuclei, including the nucleus subglomerulosus, lateral thalamic nucleus, and intermediate superficial pretectal nucleus, were absent, which suggests the corresponding functions, such as visual or gustatory function, are less developed or specialized in B. pectinirostris. These results will provide a fundamental neuroanatomical basis for future studies on neuroendocrine regulation of behavior in intertidal burrowing fish.

Nanoplastics promote arsenic-induced ROS accumulation, mitochondrial damage and disturbances in neurotransmitter metabolism of zebrafish (Danio rerio)

As a carrier, nanoplastics (NPs) can adsorb other toxic substances and thus modify their biological toxicity. Numerous studies have investigated the neurotoxic of high concentrations of arsenic (As, 2.83 mg/L-5 mg/L). However, it is still unknown whether the relatively low environmentally relevant concentrations of As (200 μg/L) can damage the structure and function of fish brains with the presence of NPs. In this study, zebrafish were exposed to polystyrene NPs, As and their mixture for 30 days respectively. Firstly, we found that the presence of NPs promoted the accumulation of As in zebrafish brains. Thereby the co-exposure of NPs and As further promoted the production of reactive oxygen species (ROS) in zebrafish brains compared with the single exposure of NPs or As, resulting in severe oxidative stress. Moreover, accumulated ROS directly damaged the mitochondrial membrane and mtDNA in zebrafish brains. Moreover, the mitochondrial damage was further aggravated due to inhibited mitochondrial fusion and activated mitochondrial division and mitophagy. Ultimately, the co-exposure led to mitochondrial damage in the zebrafish brain. Damaged mitochondria may not meet the high energy metabolic requirement for neuronal function. As a result, the normal function of nerve cells was adversely affected and eventually cell apoptosis may occur. Besides, the co-exposure caused more significant structural alterations in zebrafish brain tissue. Finally, the co-exposure of NPs and As caused abnormal biosynthesis and degradation of dopamine and acetylcholine. These resulted in decreased dopamine levels and increased acetylcholine levels in zebrafish brains. In conclusion, the presence of NPs promoted the accumulation of As, thereby inducing severe oxidative stress, which caused structural alterations and mitochondrial damage in the zebrafish brain, thus disordering neuromodulation, which may ultimately cause neurological dysfunction in zebrafish. This study will provide a risk assessment for evaluating the biotoxicity of NPs and As to fish and even other animals.

Dydrogesterone disrupts lipid metabolism in zebrafish brain: A study based on metabolomics and Fourier transform infrared spectroscopy

Brain is a potential target for neuroprogestogens and/or peripheral progestogens. Previous studies reported that expression of genes about steroidogenesis, reproduction, cell cycle, and circadian rhythm in zebrafish brain could be affected by progestogens. However, there are limited information from metabolites or biomacromolecules aspects, leaving an enormous gap in understanding toxic effects of progestogens on fish brain. In this study, we exposed zebrafish embryos to 2.8, 27.6, and 289.8 ng/L dydrogesterone (DDG, a synthetic progestogen) until sexual maturity (140 days). LC-MS and GC-MS based untargeted metabolomics and Fourier-transform infrared (FTIR) spectroscopy were then performed to investigate the metabolic profiles and macromolecular changes of brain of these zebrafish. The results from multivariate statistical analysis of metabolite features showed a clear separation between different treatment groups of both female and male zebrafish brains. DDG exposure increased the levels of cholesterol, saturated fatty acids, and nucleoside monophosphates, but decreased the contents of polyunsaturated fatty acids (PUFAs), lysophosphatides, and nucleosides in dose-dependent manner. FTIR results indicated that DDG exposure led to accumulation of saturated lipids, reduction of nucleic acids and carbohydrates, and alteration of protein secondary structures. The findings from this study demonstrated that DDG could affect contents of metabolites and biomacromolecules of zebrafish brain, which may finally lead to brain dysfunctions.

Heat waves harm fish brains

Climate change is causing heatwaves to become longer, more frequent and just plain hotter. For many of us, dealing with oppressive heat comes with several unpleasant challenges, from profuse sweating to feeling tired and sluggish. Humans, however, are not the only ones suffering through unprecedented heatwaves in a warming climate. In a ground-breaking study by Anna Andreassen and her team at the Norwegian University of Science and Technology, the researchers investigated what happens to the brains of larval zebrafish (Danio rerio) during extreme heatwaves, particularly as temperatures approach the upper limit of their heat tolerance. For these small fish, the consequences of unbearable heat are far worse than becoming a little sweaty.Fish can only tolerate temperatures so high. At some point, they lose the ability to swim properly and assume the ‘belly up’ position (termed loss of equilibrium), an indicator of imminent death. For decades, biologists have wondered what happens in the body of fish at their upper temperature limit that prompts this behaviour. Andreassen and her team set out to solve this mystery by testing whether going belly up is caused by the brain not communicating properly with the rest of the body. This miscommunication is thought to occur because high temperatures stop nerve cells in the brain from functioning as they should. But first, the researchers needed a way to visualize the fish's brain activity at extremely high temperatures. Thanks to advances in genetic technology, they were able to study genetically modified zebrafish whose brains emit a fluorescent light when their neurons are active.The researchers gradually increased the water temperature in the tank and observed the nerve cell activity of the genetically modified zebrafish using a microscope that could detect fluorescent light. At their upper temperature limit (approximately 40.9°C), the fish's brains showed very little fluorescence, indicating that the nerve cells were largely inactive. At this temperature, the larval fish were also no longer responsive to stimuli, such as bright lights flickering in front of their eyes. Interestingly, when the water temperature was raised by only 0.5°C above the upper temperature limit, something unexpected happened – the whole brain lit up as if the fish were having a seizure! This seizure-like activity was a sign that the brain had become completely depolarized, meaning that its nerve cells were firing on all cylinders, but not in a controlled manner. As this seizure-like event occurred at temperatures only slightly higher than the upper temperature limit, the team concluded that this is not what causes fish to lose equilibrium. Rather, they suggest that impaired neuron activity at the upper temperature limit is the mechanism underpinning this dangerous phenomenon.The researchers decided to take their study one step further to determine why neurons stop working at the upper temperature limit. They had a hunch that high temperatures limit how much oxygen gets to the brain, which then impairs how its nerve cells function. Andreassen and her team repeated the heat ramping experiment, but this time at high, medium and low oxygen levels. They discovered that larvae exposed to high oxygen levels in the water did better at high temperatures than those in low oxygen; the fish had higher brain activity and recovered faster after being exposed to their upper temperature limit. Overall, these findings suggest that the amount of oxygen in the water plays an important role in controlling how the brain communicates with the body at extremely high temperatures. So, the next time you're sweating profusely in the midst of a summer heatwave, take a deep breath and be thankful that your brain function has remained intact.

Tissue-specific accumulation, depuration, and effects of perfluorooctanoic acid on fish: Influences of aqueous pH and sex

Perfluorooctanoic acid (PFOA) is widely distributed in nature, particularly in aquatic environments. Its bioaccumulation and toxicity in aquatic organisms can be affected by both the chemical status of PFOA in water and the physiology of the organism. However, research on the patterns of these effects is scarce. In this study, we investigated the influence of aqueous pH (pH 6, acidic; pH 7.5, neutral; pH 9, basic) and fish sex on PFOA uptake, clearance, and biochemical effects in crucian carp (C. auratus) using flow-through exposure. In the 17-d kinetic experiment, PFOA bioaccumulation adhered to a uniform first-order model in which PFOA uptake rates from water to blood and liver in acidic conditions were faster than those in other conditions, indicating possible acidic pH influence on PFOA uptake. PFOA clearance rates in these compartments of males were slower than in females, which was attributed to the notably stronger expression of Oat2 (organic anion transporter 2, responsible for reabsorption) in the kidneys of males. Similar responses were observed for peroxisome proliferation-related biomarkers at different pH levels and in different sexes. These biochemical responses were driven by the internal concentrations of PFOA. The inhibition acetylcholinesterase activity in the fish brain was closely linked to changes in P-glycoprotein content, demonstrating a protective relationship. Collectively, an aqueous pH lower than 7.5 might affect the uptake of PFOA by fish. The clearance discrepancies between the sexes highlight the importance of anion carriers for ionizable organic compounds in aquatic organisms.

Vitamin B12 alleviates malathion-induced toxicity in zebra fish by regulating cytochrome P450 and PgP expressions

The indiscriminate and rampant use of pesticides has raised serious concerns regarding their toxic impact on non-target organisms which underlines need for the development of an effective antidote. Metabolic activation of organophosphate pesticides by the phase I enzyme, cytochrome P450 plays a key role in influencing pesticide-toxicity. In this study, we have investigated the effect of environmentally relevant malathion concentration (100 μg/L) alone and in combination with vitamin B12 on the expression of genes related to xenobiotic metabolism such as CYP enzymes, PgP and the key oxidative stress responsive transcription factor, Nrf2 in zebra fish liver and brain. Expressions of Nrf2-trasncribed antioxidant genes and their activities were also measured. Administration of vitamin B12 successfully revived motor functions by modulation of AchE activity. Mechanistically, vitamin B12 was demonstrated to alleviate oxidative stress which was accompanied by decreased phase-I enzyme cyp3c1 and increased pgp expressions.

Physical and social enrichment influences the adaptability-related behaviors of black rockfish Sebastes schlegelii: An effect mediated by social behaviors, HPI axis and neurogenesis

Environmental enrichment is a promising method to increase fish ecological fitness in hatchery release and to improve fish welfare in the aquaculture industry. However, little is known about the effects of physical and social enrichment on fish behavioral development and the relevant regulatory mechanisms. To address this knowledge gap, a typical aquaculture fish, black rockfish Sebastes schlegelii, was exposed to contrasting environments (i.e., physically enriched environment vs. barren environment, and socially low-density environment vs. high-density environment) for six weeks. Subsequently, the adaptability-related behaviors and social interactions during the captive period were determined, and stress-related physiological parameters and neurogenesis-related gene markers were measured. In general, the fish from an enriched environment expressed significantly higher sheltering propensity and anti-predator ability while less risk-taking frequency than the fish from a barren environment. And meanwhile, the fish from a low-density environment presented significantly less risk-taking behavior and more anti-predator responses than high-density fish. A structurally barren environment significantly increased fish aggressive frequency and locomotor activity compared with an enriched environment, whereas the social environment did not affect fish social interactions. For physiological status, the hypothalamus-pituitary-interrenal (HPI) axis and corticosteroid receptor system activities of barren fish were significantly higher than those of enriched fish, and meanwhile, the high-density fish also presented significantly higher physiological stress than low-density fish. For neurogenesis processes, an enriched environment did not affect fish brain cell proliferation but increased telencephalon neuronal differentiation ratio and immature neuron number. In contrast, a low-density environment significantly stimulated cell proliferating activity in telencephalon but did not affect brain neuronal differentiation activity. These novel results verified the conspicuous effects of physical and social environments on the adaptability-related behaviors in aquaculture fish, and finally, we proposed a novel regulatory pathway for fish behavioral plasticity, i.e., environmental stimuli - social interactions - HPI axis - corticosteroid receptor system - neurogenesis - adaptability-related behaviors. These results may lay the foundations for restoring fishery resources and for improving fish welfare, add novel knowledge to fish biology and environmental enrichment framework, and help deeply understand the mechanisms of environmental effects on marine animal behaviors.