Novel spikey ionocytes are regulated by cortisol in the skin of an amphibious fish

Cortisol is a major osmoregulatory hormone in fishes. Cortisol acts upon the gills, the primary site of ionoregulation, through modifications to specialized ion-transporting cells called ionocytes. We tested the hypothesis that cortisol also acts as a major regulator of skin ionocyte remodelling in the amphibious mangrove rivulus ( Kryptolebias marmoratus ) when gill function ceases during the water-to-land transition. When out of water, K. marmoratus demonstrated a robust cortisol response, which was linked with the remodelling of skin ionocytes to increase cell cross-sectional area and Na + -K + -ATPase (NKA) content, but not when cortisol synthesis was chemically inhibited by metyrapone. Additionally, we discovered a novel morphology of skin-specific ionocyte that are spikey with multiple cell processes. Spikey ionocytes increased in density, cell cross-sectional area and NKA content during air exposure, but not in metyrapone-treated fish. Our findings demonstrate that skin ionocyte remodelling during the water-to-land transition in amphibious fish is regulated by cortisol, the same hormone that regulates gill ionocyte remodelling in salinity-challenged teleosts, suggesting conserved hormonal function across diverse environmental disturbances and organs in fishes.

Exposure to Oxy-Tetracycline Changes Gut Bacterial Community Composition in Rainbow Trout: A Preliminary Study

The extensive use of antibiotics is evident in most of the livestock and aquaculture management for inhibiting pathogen infection. Korean aquaculture depends on the usage of oxy-tetracycline for growing rainbow trout. Hence, this study was conducted to evaluate the changes in gut bacterial community profiles of rainbow trout exposed to oxy-tetracycline and predict the metabolic functioning of the bacterial community. The gut bacterial community composition of oxy-tetracycline treated fish was assessed by amplicon sequencing targeting the 16S rRNA gene of bacteria and comparing with the control group that did not receive any antibiotic. The principle coordinate analysis and non-metric multidimensional scaling analysis had shown two distinct clusters that implies the changes in community composition. In phyla level, the relative abundances of Tenericutes and Firmicutes were observed to be significantly higher in oxy-tetracycline treated fish compared to the control. Furthermore, the prediction based metabolic profiling revealed the processes that are affected due to the shift in community profiles. For example, metabolic functioning of membrane efflux system, amino acid metabolism and glycolysis were significantly higher in oxy-tetracycline treated fish compared to the control. This study describes alteration in gut bacterial community composition and potential metabolic profiles of the community that might be responsible for surviving in antibiotic rich environment.

A Zebrafish Model of Neurotoxicity by Binge-Like Methamphetamine Exposure

Hyperthermia is a common confounding factor for assessing the neurotoxic effects of methamphetamine (METH) in mammalian models. The development of new models of methamphetamine neurotoxicity using vertebrate poikilothermic animals should allow to overcome this problem. The aim of the present study was to develop a zebrafish model of neurotoxicity by binge-like methamphetamine exposure. After an initial testing at 20 and 40 mg/L for 48 h, the later METH concentration was selected for developing the model and the effects on the brain monoaminergic profile, locomotor, anxiety-like and social behaviors as well as on the expression of key genes of the catecholaminergic system were determined. A concentration- and time-dependent decrease in the brain levels of dopamine (DA), norepinephrine (NE) and serotonin (5-HT) was found in METH-exposed fish. A significant hyperactivity was found during the first hour of exposure, followed 3 h after by a positive geotaxis and negative scototaxis in the novel tank and in the light/dark paradigm, respectively. Moreover, the behavioral phenotype in the treated fish was consistent with social isolation. At transcriptional level, th1 and slc18a2 (vmat2) exhibited a significant increase after 3 h of exposure, whereas the expression of gfap, a marker of astroglial response to neuronal injury, was strongly increased after 48 h exposure. However, no evidences of oxidative stress were found in the brain of the treated fish. Altogether, this study demonstrates the suitability of the adult zebrafish as a model of METH-induced neurotoxicity and provides more information about the biochemical and behavioral consequences of METH abuse.

Effect of Water Temperature on the Depletion of Eugenol in Sea Bass under the Simulated Settings in Handling and Transport

The edible safety of eugenol-treated fish is one of the concerns limiting the anesthetic applied in the aquaculture industry. The depletion of eugenol was investigated at different water temperatures under the simulated settings of sea bass handling and transport. Sea bass was exposed to eugenol at a concentration of 60 mg/L for 3 min, then immediately transferred to clean water to be purged for 24 h and sampled at different time intervals. The left fish were re-exposed to eugenol in a repeat of the first exposure, purged for 48 h in clean water, and sampled for eugenol detection. Under the simulated settings, the sea bass could accumulate more eugenol residue in fillet when exposed to water at a temperature of 20 °C than that at 13 °C. However, eugenol could be depleted much faster when the sea basses were exposed to the higher water temperature. The half-lives of eugenol in sea bass were 0.28 h and 0.29 h for the first and second purging stage at a water temperature of 20 °C, while at 13 °C, the half-lives were 2 and 4.5 h, respectively. Therefore, increasing the water temperature may be an effective way to accelerate eugenol depletion in fish fillet and reduce exposure risk for the consumer.

Toxicity Evaluation of Arsenic Nanoparticles on Growth, Biochemical, Hematological, and Physiological Parameters of Labeo rohita Juveniles

The present study aims to assess the induced nanotoxicity of arsenic nanoparticles (AsNPs) on different organs of fresh water fish Labeo rohita. AsNPs were synthesized by chemical reduction method using sodium arsenite as precursor, ice-cold sodium borohydride as reducing agent, and sodium hydroxide to adjust the solution pH. The synthesized AsNPs were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) for optical, structural, and morphological investigations. The UV-Vis absorption peaks occurring at around 300 nm indicated the presence of AsNPs in colloidal sample. The rhombohedral crystalline nature and metallic purity of AsNPs with crystallite size of 30 ± 1 nm were confirmed by characteristic peaks of XRD pattern. The SEM micrograph revealed the almost spherical shape and 40 ± 10 nm average size prepared AsNPs. For assessment of induced nanotoxicity, juveniles of Labeo rohita (L. rohita) were exposed to three different concentrations of AsNPs (namely, 1, 10, and 20 mg/L) for 30 days (n = 15 per group), and the control fish was kept untreated. It was observed that the routine behavior activities (such as swimming, mutual interactions, and feed intake) were affected by AsNPs. The growth of AsNPs treated fish was found retarded as compared to the control fish. Total erythrocyte count, total leukocyte count, and hemoglobin and hematocrit values were low in the AsNPs treated fish. Immunobiochemical assays revealed that protein level was altered in the AsNPs treated fish. The levels of antioxidant enzymes catalase and superoxide dismutase were low in the treated fish. The histological alteration induced by AsNPs in liver, gills, and kidneys demonstrated the damage in form of glomerulus shrinkage, vacuolation, inflammation, necrosis, lamellar disorganization, and hemorrhage in comparison with untreated fish. The results of the present study indicate that AsNPs exposure causes behavior, growth, hematology, immunobiochemical, and histological shortcomings in L. rohita.

Sodium chloride bath – A cheap and safe tool for antiparasitic treatment of fish

Sodium chloride is widely used in aquaculture due to its antiparasitic effects and its ability to reduce stress during fish transport and manipulation. The aim of this study was to assess the safety of short-term exposure to sodium chloride for the common carp (Cyprinus carpio). In our experiment, fish were placed into a sodium chloride bath (c = 30 g l^–1; T = 30 min; t = 20 °C) and the effects of the treatment were assessed immediately after the bath (T0) and 24, 48 and 240 h later (T24, T48 and T240, respectively), with non-treated fish serving as control groups. Though significant differences compared to the controls were observed in the treated fish sampled at T0, T24 and T48, these effects were only temporary and all the affected parameters (i.e., haemoglobin, haematocrit, plasmatic lactate, cholesterol, alanine aminotransferase, albumin, phosphorus and ceruloplasmin) had completely recovered within 10 days of exposure, suggesting that the treatment of carp with a sodium chloride bath represents a safe approach suitable for therapy of parasitic infections.

Biomarker approach for assessing chronic toxicity of Captan® herbicide using haematological, growth, endocrine and biochemical endpoints in air breathing catfish, Clarias batrachus

This study was conducted to determine the sub-lethal toxicity of Captan® on selected hematological (Hb, HCT, MCH) growth (K-factor, HSI, SGR), biochemical (serum glucose, protein), and endocrine parameters (growth hormone, T3 and T4) in Clarias batrachus under chronic exposures. Captan® was administered at predetermined exposure concentrations (0.53 and 1.06 mg/L) and monitored at day 15, 30 and 45 of the experimental periods. The experimental groups showed significantly lower values (p < 0.05) of haemoglobin content, haematocrit, MCH in Captan® exposed fish compared to control. Serum glucose was significantly higher (p < 0.05) in treated fish compared to the control group; reverse was the case for serum protein concentrations (p < 0.05). Assessment of growth parameters revealed significantly higher k-factor and SGR in control fish. HSI was however higher in treated fish which highlights the possibility of liver hypertrophy and hyperplasia of liver cells due to higher exposure and uptake of the herbicide. Endocrine responses (T3 and T4) emerged as the most sensitive biomarker category, depicting modulated responses between sub-chronic exposure at day-15 and chronic responses at day-45. In general, the study findings using these biomarkers indicate that Captan® exposures are capable of inducing stress-specific effects at the biochemical and physiological levels negatively impacting the overall health and longevity of such animals. The use of the IBR index provided a visual and easily comprehensible depiction of toxicity effects and biomarker responses in laboratory exposed fish and we anticipate a greater applicability in biomarker data from the wild which are largely heterogenous.

Extremely dilution of Strychnos Nux vomica mitigates alcohol-induced reduction in enthalpies associated with free water molecules in fish brain

Background: Alcoholism is a global health problem. Extract of the seeds of Strychnos Nux vomica and its high dilution have long been used in homeopathy for alcohol induced diseases of patients. Alcoholism leads to reduced brain volume. Glial cells like astroglia contain large number of water channel proteins or aquaporin (AQP4) which mediate glial oedema resulting from ethanol intoxication. Nux vomica, a homeopathic drug of plant origin, is known to counteract alcohol effect. Aim: The objective of this present study is to find out the level of free water molecules in the brain of a teleost fish under ethanol intoxication. The other purpose is to determine whether Nux vomica could restore the level of free water in the alcohol treated fish. Methodology: One group of fish was exposed to 456 mM ethanol for 30 min, another exposed first to a solution of Nux vomica 200c for 20 min and then to 456 mM ethanol for 30 min. The third group served as an untreated control. The mid brain of each fish was kept in an aluminium sample pan and its free water level was assessed by differential scanning calorimetry (DSC). Data were analyzed by ANOVA. Results and discussion: The results show that there was no significant variation in melting and freezing temperature of brain samples but the enthalpies, both freezing and melting varied significantly (P

Extremely Dilution of Strychnos Nux vomica Mitigates Alcohol-Induced Reduction in Enthalpies Associated With Free Water Molecules in a Fish Brain

Introduction Alcohol intoxication affects aquaporins in the glial cells of brain resulting in oedema. Nux vomica, a homeopathic drug of plant origin, is known to counteract alcohol effect. The objective of this present study is to find out the level of free water molecules in the brain of a teleost fish under ethanol intoxication. The second objective is to determine whether Nux vomica could restore the level of free water in the alcohol treated fish. Materials and methods One group of fish was exposed to 456 mM ethanol for 30 min, another exposed first to a solution of Nux vomica 200c for 20 min and then to 456 mM ethanol for 30 min. The third group served as an untreated control. The mid brain of each fish was kept in an aluminium sample pan and its free water level was assessed by differential scanning calorimetry (DSC). Results All alcohol treated fish showed significant reduction in the level of free water molecules as compared to the untreated control. Treatment with Nux vomica increased the level of free water in the brain significantly as compared to the untreated alcoholic group. Conclusion Alcohol intoxication reduces free water molecules in the fish brain. Nux vom might have acted on aquaporins in the glial cells thereby increasing the level of free water in the brain.

Developmental thyroid disruption causes long-term impacts on immune cell function and transcriptional responses to pathogen in a small fish model

Current evidence suggests thyroid hormones (THs) impact development of the immune system, but few studies have explored the connection between the thyroid and immune systems, especially in fish. This is important as some environmental contaminants disrupt TH homeostasis and may thus have negative impacts on the immune system. To determine the long-term consequences of early life stage (ELS) hypothyroidism on immune function, fathead minnows were exposed to the model thyroid hormone suppressant propylthiouracil (PTU) from < 1 to 30 days post hatch. Fish were transferred to clean water and raised to adulthood (5–7 months post hatch) at which time, several aspects of immune function were evaluated. Ex vivo assessment of immune cell function revealed significant decreases (1.2-fold) in the phagocytic cell activity of PTU-treated fish relative to the controls. Fish were also injected with Yersinia ruckeri to evaluate their in vivo immune responses across a suite of endpoints (i.e., transcriptomic analysis, leukocyte counts, spleen index, hematocrit, bacterial load and pathogen resistance). The transcriptomic response to infection was significantly different between control and PTU-treated fish, though no differences in bacterial load or pathogen resistance were noted. Overall, these results suggest that early life stage TH suppression causes long-term impacts on immune function at the molecular and cellular levels suggesting a key role for TH signaling in normal immune system development. This study lays the foundation for further exploration into thyroid-immune crosstalk in fish. This is noteworthy as disruption of the thyroid system during development, which can occur in response to chemicals present in the environment, may have lasting effects on immune function in adulthood.