Effects of cadmium on hypoxia-induced expression of hemoglobin and erythropoietin in larval sheepshead minnow, Cyprinodon variegatus

Melatonin as an Ameliorative Agent Against Cadmium- and Lead-Induced Toxicity in Fish: an Overview

Diverse anthropogenic activities and lack of knowledge on its consequences have promoted serious heavy metal contaminations in different aquatic systems throughout the globe. The non-biodegradable nature of most of these toxic heavy metals has increased the concern on their possible bioaccumulation in aquatic organisms as well as in other vertebrates. Among these aquatic species, fish are most sensitive to such contaminated water that not only decreases their chance of survivability in the nature but also increases the probability of biomagnifications of these heavy metals in higher order food chain. After entering the fish body, heavy metals induce detrimental changes in different vital organs by impairing multiple physiological and biochemical pathways that are essential for the species. Such alterations may include tissue damage, induction of oxidative stress, immune-suppression, endocrine disorders, uncontrolled cell proliferation, DNA damage, and even apoptosis. Although uncountable reports have explored the toxic effects of different heavy metals in diverse fish species, but surprisingly, only a few attempts have been made to ameliorate such toxic effects. Since, oxidative stress seems to be the underlying common factor in such heavy metal-induced toxicity, therefore, a potent and endogenous antioxidant with no side effect may be an appropriate therapeutic solution. Apart from summarizing the toxic effects of two important toxicants, i.e., cadmium and lead in fish, the novelty of the present treatise lies in its arguments in favor of using melatonin, an endogenous free radical scavenger and indirect antioxidant, in ameliorating the toxic effects of heavy metals in any fish species.

Investigation on Immune-Related Protein (Heat Shock Proteins and Metallothionein) Gene Expression Changes and Liver Histopathology in Cadmium-Stressed Fish

Heat shock proteins (HSP) are highly conserved in their structure and released in case of stress. Increased metallothionein (MT) synthesis is associated with increased capacity for binding heavy metals. Healthy juveniles of grass carp were exposed to sublethal dose (1.495 mg L⁻¹) of cadmium for 28 days. Simultaneously, a control group was also run to compare difference of total RNA expression levels in cadmium-treated and control groups. The cadmium levels in the tissues of treated fish recorded were 1.78 ± 0.10 mg L⁻¹, 1.60 ± 0.04 mg L⁻¹, and 2.00 ± 0.05 mg L⁻¹, respectively. Several histological alterations including edema, hemorrhage, dilated sinusoids, hypertrophy, hyperplasia, congestion of central vein, and nuclear alterations were observed in cadmium-exposed fish. Stress gene (metallothionein and heat shock proteins) mRNA transcription levels were studied by mRNA extraction and cDNA preparation by using PCR. The expression level of heat shock protein gene was higher as compared to metallothionein and beta-2-microglobulin gene after cadmium exposure. This study reports various stress-related immune-responsive changes of immune proteins, heat shock proteins, metallothionein, and histopathological changes in fish due to cadmium toxicity that make the fish immunocompromised which may be considered as the biomarkers of cadmium toxicity in other experimental species.

Galaxolide and tonalide modulate neuroendocrine activity in marine species from two taxonomic groups

Galaxolide (HHCB) and tonalide (AHTN) are polycyclic musk compounds (PMCs) used in household and personal care products that have been included on the list as emerging contaminants of environmental concern due to their ubiquity in aquatic and terrestrial environments. There still exists a dearth of information on the neurotoxicity and endocrine disrupting effects of these contaminants, especially for marine and estuarine species. Here, we assessed the neuroendocrine effects of HHCB and AHTN using adult clams, Ruditapes philippinarum, and yolk-sac larvae of sheepshead minnow, Cyprinodon variegatus. The clams were treated with concentrations (0.005-50 μg/L) of each compound for 21 days. Meanwhile, sheepshead minnow larvae were exposed to 0.5, 5 and 50 μg/L of HHCB and AHTN for 3 days. Enzyme activities related to neurotoxicity (acetylcholinesterase - AChE), neuroendocrine function (cyclooxygenase - COX), and energy reserves (total lipids - TL) were assessed in R. philippinarum. Gene expression levels of cyp19 and vtg1 were measured in C. variegatus using qPCR. Our results indicated induction of AChE and COX in the clams exposed to HHCB while AHTN exposure significantly inhibited AChE and COX. Gene expression of cyp19 and vtg1 in yolk-sac C. variegatus larvae exposed to 50 μg/L AHTN was significantly downregulated versus the control. The results of this study demonstrate that HHCB and AHTN might pose neurotoxic and endocrine disrupting effects in coastal ecosystems.

Insights into the heavy metal-induced immunotoxic and genotoxic alterations as health indicators of Clarias gariepinus inhabiting a rivulet

There is a dire need to assess the quality of fishes transported for human consumption as lately, their health is challenged because of anthropogenic activities. Heavy metals with a long environmental persistence are toxic to fishes and the humans. The study was conducted to evaluate the impact of heavy metals on Clarias gariepinus inhabiting popular Ganges rivulet at Narora (28.18° E, 78.39° N). The limnological values deviated from the international Standards (USEPA, WHO). Higher total dissolved solids (859 mg/L), total suspended solids (406 mg/L), low dissolved oxygen (5.60 mg/L), and pH (5.21) indicated the presence of contaminants. Heavy metals estimated followed the order Cd > Ni > Cu > Cr. Serum enzymes (hepatic and renal markers) viz., aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) were higher than the normal, whereas, creatine kinase (CK) was considerably low in both male and female fish. Stress induced was marked by elevation in cortisol and glucose. This had its impact on hematological parameters as well, as a decline in Total leucocyte count (TLC) & mean corpuscular volume (MCV) and increase in Mean cell hemoglobin (MCH) was observed. Erythrocytes also showed altered morphology. Marked histopathological alterations were observed in all immune organs (head-kidney, liver, spleen, thymus). Oxidative stress induced by heavy metals leads to the production of metal scavenging protein metallothionein (MT) and glutathione peroxidase (GPX). Maximum fold change in metallothionein (MT) gene expression was observed in the liver, followed by spleen, thymus, blood, and head-kidney. Glutathione peroxidase (GPX) gene expression was highest in the liver, followed by thymus, spleen, blood, and head-kidney. The gene expression studies further validated the increased level of heavy metals as potent contaminants of water and the non-condusive abiotic factors.

Haematopoiesis and haematopoietic organs in fish

Haematopoiesis is a complex process in which haematopoietic stem cells, the most immature elements of the haematopoietic hierarchy, proliferate and differentiate into various classes of haematopoietic progenitor cells. These progenitor cells have been shown to be able to differentiate into mature blood cells: erythrocytes, lymphocytes, thrombocytes, granulocytes, and monocytes. The pronephros, or head kidney, is a basic organ forming the blood elements, and is also a reservoir of blood cells. Basic haematopoietic structures and mechanisms in fish are similar to those functioning in other vertebrates, and all haematopoietic cell types are very similar to those of mammals.

Metallothionein Induced Time Dependent Histomorphometric Analysis of Clarias gariepinus Exposed to Cadmium

Cadmium (Cd), an extremely toxic heavy metal is extensively used in modern era because of its constructive chemical and physical properties. Recently Cd contamination was estimated in India's major cities fresh water ecosystem, which may have firm impact on human health. Hence, this study was aimed to detect the time dependent effect of cadmium in fresh water fish C. gariepinus, a bioindicator species of water pollution. In a controlled environment, fishes were exposed to cadmium for different duration and analyzed for Cd accumulation. Cd induced toxicity was assessed by estimating metallothionein biomarker protein of heavy metal toxicity and histomorphometric changes in liver and kidney. Our results revealed that fish exposed to Cd induced apoptosis in fish tissues via induction of caspases and in contrast the metallothionein was also increased consistently with different doses of Cd exposure. Hence we conclude Cd induced structural damages to fishes are attributed to induction of caspases and estimating MT level in tissues can be effective biomarker to analyze the effect of acute environmental exposure to Cd.

Intrauterine Exposure to Cadmium Reduces HIF-1 DNA-Binding Ability in Rat Fetal Kidneys

During embryonic development, some hypoxia occurs due to incipient vascularization. Under hypoxic conditions, gene expression is mainly controlled by hypoxia-inducible factor 1 (HIF-1). The activity of this transcription factor can be altered by the exposure to a variety of compounds; among them is cadmium (Cd), a nephrotoxic heavy metal capable of crossing the placenta and reaching fetal kidneys. The goal of the study was to determine Cd effects on HIF-1 on embryonic kidneys. Pregnant Wistar rats were exposed to a mist of isotonic saline solution or CdCl₂ (D_Del = 1.48 mg Cd/kg/day), from gestational day (GD) 8 to 20. Embryonic kidneys were obtained on GD 21 for RNA and protein extraction. Results show that Cd exposure had no effect on HIF-1α and prolyl hydroxylase 2 protein levels, but it reduced HIF-1 DNA-binding ability, which was confirmed by a decrease in vascular endothelial growth factor (VEGF) mRNA levels. In contrast, the protein levels of VEGF were not changed, which suggests the activation of additional regulatory mechanisms of VEGF protein expression to ensure proper kidney development. In conclusion, Cd exposure decreases HIF-1-binding activity, posing a risk on renal fetal development.

Molecular evolution and expression of oxygen transport genes in livebearing fishes (Poeciliidae) from hydrogen sulfide rich springs

Hydrogen sulfide (H2S) is a natural toxicant in some aquatic environments that has diverse molecular targets. It binds to oxygen transport proteins, rendering them non-functional by reducing oxygen-binding affinity. Hence, organisms permanently inhabiting H2S-rich environments are predicted to exhibit adaptive modifications to compensate for the reduced capacity to transport oxygen. We investigated 10 lineages of fish of the family Poeciliidae that have colonized freshwater springs rich in H2S—along with related lineages from non-sulfidic environments—to test hypotheses about the expression and evolution of oxygen transport genes in a phylogenetic context. We predicted shifts in the expression of and signatures of positive selection on oxygen transport genes upon colonization of H2S-rich habitats. Our analyses indicated significant shifts in gene expression for multiple hemoglobin genes in lineages that have colonized H2S-rich environments, and three hemoglobin genes exhibited relaxed selection in sulfidic compared to non-sulfidic lineages. However, neither changes in gene expression nor signatures of selection were consistent among all lineages in H2S-rich environments. Oxygen transport genes may consequently be predictable targets of selection during adaptation to sulfidic environments, but changes in gene expression and molecular evolution of oxygen transport genes in H2S-rich environments are not necessarily repeatable across replicated lineages.

Proximate Composition and Heavy Metal Analysis of Three Aquatic Foods in Makoko River, Lagos, Nigeria

Three aquatic products, tilapia fish, lobster and crab, were collected from the landing site of fishermen in Makoko, a fishing suburb in Lagos State, Nigeria. They were analyzed for their proximate composition, and concentration of heavy metals (Cr, Cd, and Pb) was also measured in them. The nutrient values varied among the three organisms. The lobsters and crabs had higher protein values while tilapia was richer in lipid and moisture content. In most cases, these differences were not significant. The concentration of heavy metals also differed in the three organisms. All organisms had high concentrations of the three heavy metals analyzed. The heavy metal load as observed in this study is consistent with some previously reported values in literature. Plausible reasons for these differences were discussed in light of size, trophic level, choice of food of the organisms, and anthropogenic activities. It may be advisable that heavy metal concentrations are regularly monitored in edible aquatic food products so that human health is not at risk.

Alterations to Juvenile Zebrafish (Danio rerio) Swim Performance after Acute Embryonic Exposure to Sub-lethal Exposures of Hydraulic Fracturing Flowback and Produced Water

Hydraulic fracturing flowback and produced water (FPW) is a wastewater produced during fracturing activities in an operating well which is hyper saline and chemically heterogeneous in nature, containing both anthropogenic and petrogenic chemicals. Determination of FPW associated toxicity to embryonic fish is limited, while investigation into how embryonic exposures may affect later life stages is not yet studied. Zebrafish embryos (24hrs post fertilization) were acutely exposed to 2.5% and 5% FPW fractions for either 24 or 48hrs and returned to freshwater. After either 24 or 48h exposures, embryos were examined for expression of 3 hypoxia related genes. Erythropoietin (epoa) but not hypoxia inducible factor (hif1aa) nor hemoglobin -ß chain (hbbe1.1) was up-regulated after either 24 or 48h FPW exposure. Surviving embryos were placed in freshwater and grown to a juvenile stage (60days post fertilization). Previously exposed zebrafish were analyzed for both swim performance (U_crit and U_max) and aerobic capacity. Fish exposed to both sediment containing (FPW-S) or sediment free (FPW-SF) FPW displayed significantly reduced aerobic scope and U_crit/U_max values compared to control conditions. Our results collectively suggest that organics present in our FPW sample may be responsible for sub-lethal fitness and metabolic responses. We provide evidence supporting the theory that the cardio-respiratory system is impacted by FPW exposure. This is the first known research associating embryonic FPW exposures to sub-lethal performance related responses in later life fish stages.

Assessment of immune status of yellowfin seabream (Acanthopagrus latus) during short term exposure to phenanthrene

The aim of the present investigation was to assess the immune status in yellowfin seabream (Acanthopagrus latus) exposed to different concentrations of phenanthrene (Phe) for 14days. In addition, the Phe accumulation in the fish muscle was measured during the experiment. Fish were injected with different concentrations (0, 2, 20 and 40mg/kg) of Phe and samples were taken from tissue and blood of fish 1, 4, 7 and 14days after injection. Exposure of fish to Phe caused a significant decrease in white blood cells, C3 and C4 levels, lysosomal membrane stability, lysozyme activity after 4days and antibacterial activity after 7days of the experiment. In contrast, cortisol level significantly increased after 4days. The concentration of Phe in fish muscle increased rapidly after 4days. The main tissue changes observed in the head kidney including increase in melanomacrophage centers (MMCs), empty spaces between cells and hemorrhage. The degree of tissue changes ranged from normal to moderate in Phe-treated fish. The size and number of MMCs in treated fish were significantly higher than control. In conclusion, Phe toxicity in yellowfin seabream can induce increased cortisol level, tissue changes and immune suppression.

Environmentally induced tissue responses of hematopoietic system in abu mullet (Liza abu) and tiger tooth croaker (Otolithes ruber) from the Persian Gulf

The present investigation aimed to assess the possibility of using plasma levels of erythropoietin (EPO) hormone and tissue changes of hematopoietic organs as biomarkers of environmental pollution in abu mullet (Liza abu) and tiger tooth croaker (Otolithes ruber) collected from Musa Creek (northwest of the Persian Gulf). 120 L. abu and O. ruber were collected from five stations at the Musa Creek: Petrochemical, Ghanam, Doragh, Zangi and Patil stations. Blood samples were obtained from the caudal vein. Tissue samples were also taken from the spleen and head kidney, and tissue sections were prepared according to routine histological methods. The concentrations of Hg, Pb, Zn, Cu, and Cd were also measured in the sediment samples. The minimum level of EPO and the most severe tissue changes were determined in fish collected near a Petrochemical station. This station is adjacent to the Imam Khomeini Petrochemical Complex and receives highly contaminated effluents from this complex. The highest degree of contamination (C_d) also belonged to this station. The fish collected from the Patil station represented the highest EPO level and the least tissue changes. This station exhibited a lesser degree of contamination. Based on the results, there was a significant correlation between the plasma level of EPO hormone and the degree of environmental contamination.

Gene Expression Profiling in Fish Toxicology: A Review

In this review, we present an overview of transcriptomic responses to chemical exposures in a variety of fish species. We have discussed the use of several molecular approaches such as northern blotting, differential display reverse transcription-polymerase chain reaction (DDRT-PCR), suppression subtractive hybridization (SSH), real time quantitative PCR (RT-qPCR), microarrays, and next-generation sequencing (NGS) for measuring gene expression. These techniques have been mainly used to measure the toxic effects of single compounds or simple mixtures in laboratory conditions. In addition, only few studies have been conducted to examine the biological significance of differentially expressed gene sets following chemical exposure. Therefore, future studies should focus more under field conditions using a multidisciplinary approach (genomics, proteomics and metabolomics) to understand the synergetic effects of multiple environmental stressors and to determine the functional significance of differentially expressed genes. Nevertheless, recent developments in NGS technologies and decreasing costs of sequencing holds the promise to uncover the complexity of anthropogenic impacts and biological effects in wild fish populations.

Metabolic capacities of common carp (Cyprinus carpio) following combined exposures to copper and environmental hypoxia

In aquatic ecosystems, a decline in water O2 level is the main factor that can release heavy metal ions from top sediment layer. Therefore, hypoxia in turn, and in association with heavy metals might provide undesirable environment and impairs physiological functions of aquatic animals. To address this, metabolic capacities, including standard metabolic rate (SMR), maximum metabolic rate (MMR), aerobic scope (AS) and factorial aerobic scope (FAS) of common carp were determined following exposures to different levels of water-borne Cu(2+) as well as hypoxia. Treatments for Cu(2+) were included: 100% (acute), 50% (sub-lethal) and 10% (chronic) of LC50-96h for immediately, 24h and 7 days exposures respectively. Hypoxia treatments were assigned as acute for immediately, sub-lethal for 24h and chronic for 7 days. Combined effects of treatments were also considered as acute Cu(2+)+hypoxia, sub-lethal Cu(2+)+hypoxia and chronic Cu(2+)+hypoxia. While SMR of carp was reduced by chronic hypoxia, significant (P<0.05) increase was observed during acute hypoxia, as compared with control. The MMR and AS were significantly reduced (P<0.05) following all hypoxia treatments. The acute and chronic Cu(2+) treatments showed significant (P<0.05) increases in SMR and MMR values. All acute and sub-lethal combined treatments showed significant (P<0.05) reductions in SMR, MMR and AS values, whilst chronic combined treatments showed generally increasing trends for MMR and AS. PCrit was relatively reduced following all treatments except for acute and sub-lethal Cu(2+)-treated fish that showed higher value (P<0.05) and no change respectively. Although all Cu(2+) treatments increased the number of mucus cell, hypoxia treatments did not show any remarkable differences when compared with control group. In general, the results of present study reveal that hypoxia acts as limiting stressor whilst Cu(2+) do act as loading stressors in the case of common carp metabolism. The interactive exposures mostly showing a synergist effect in all metabolic capacities with an exception for chronic treatments.

Heavy Metals and Histopathological Alterations in Salminus franciscanus (Lima & Britski, 2007) (Pisces: Characiformes) in the Paraopeba River, Minas Gerais, Brazil

Cu, Pb, Cd, Zn, Cr, Hg, and Fe in the liver, spleen and muscle, of the fish Salminus franciscanus, from two sections of Paraopeba River, highly affected by anthropogenic influences, was detected in levels above those recommended for human consumption. Positive correlations between fish size and levels of metals were detected for Cd, Pb, Hg, and Zn. In the livers, areas with lipid accumulation and pigmented macrophages were also observed, as was fibrosis of the spleen in the parenchymal area through the presence of pigmented macrophages. The diameter of vitellogenic follicles was less and the frequency of atresia was higher in fish from section A. Thus, our study showed that beyond the risk to the population that eats S. franciscanus from the Paraopeba River, we should also consider the risk to the conservation of this species, since histopathological changes were detected in target organs and in some reproductive parameters.

Exposure of Persian sturgeon (Acipenser persicus) to cadmium results in biochemical, histological and transcriptional alterations

Sturgeon is one of the endangered families of fish in the Caspian Sea region, where there is up to 80% of their global caching. Unfortunately, in recent years, increase of pollutants has been resulted in their total population reduction. Due to their benthic nature, sturgeons are at great risk of exposing to contaminants such as cadmium. Despite their endangered status in the Caspian Sea, there are only a few studies on characterizing the relative sensitivity of sturgeons to cadmium. Adverse effects associated with pollution on angiogenesis are mediated by hypoxia inducing factor-1 (HIF-1) and vascular endothelial growth factor (VEGF). In this investigation, gene expression of two distinct HIFs-1, HIF-1α and HIF-2α, and VEGF was investigated at the mRNA transcript levels after exposure of Persian sturgeon (Acipenser persicus) to cadmium. VEGF, HIF-1α and HIF-2α expressions in treated Persian sturgeon were greater than controls. Significant increases (P<0.05) were also observed in cortisol and glucose levels compared to the control group especially in the fish exposed to higher cadmium concentration (800 μg/L). Plasma aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactic acid dehydrogenase (LDH) levels were increased in the cadmium-exposed fish, although the observed increases were not significant between the control and 200 μg/L cadmium treatment at some sampling time points. Gill tissues also showed histopathological changes in the cadmium treatments. Overall, results indicated that cadmium resulted in some alterations in biochemical parameters, mRNA transcript level expression of two important angiogenesis related genes as well as histological alterations in Persian sturgeon.

Exposure of the gilthead seabream (Sparus aurata) to sediments contaminated with heavy metals down-regulates the gene expression of stress biomarkers

Heavy metals incidence in the aquatic environment and its accumulation in fish are under constant review. Gilthead seabream (Sparus aurata) specimens were exposed for two weeks to sediments highly concentrated in metals, collected at the Portman Bay (Murcia, Spain). The metals bioaccumulation was tested in liver, muscle and skin. The potential of the sediment exposure to induce variation of the stress biomarkers genes was conducted in liver and skin. Results revealed that sediments were highly contaminated with metals. However, following 2 weeks exposure to the sediments, Cd accumulates only in liver. Interestingly, the expression of the genes mta, hsp 70 and hsp 90 were significantly down-regulated in skin. Nevertheless, cyp1a1 gene was up-regulated only in liver. Results uphold that the stress response magnitude was organ-dependent and the skin was the most responsive tissue to metal stress conditions. These results suggest that skin should be considered as target organ for biomarkers analysis in fishes.

Application of biomarkers in Epaulet grouper (Epinephelus stoliczkae) to assess chromium pollution in the Chabahar Bay and Gulf of Oman

In the present study plasma levels of erythropoietin (EPO) hormone and kidney histological changes were assessed as biomarkers to evaluate the chromium pollution in Epaulet grouper (Epinephelus stoliczkae) obtained from different areas in Chabahar Bay and Gulf of Oman. Chemical analyses included the evaluation of chromium in the fish kidney tissue and sediment. The highest and lowest concentrations of chromium were measured in the kidney of fish and sediment collected from Konarak (47.53±1.23 and 110±1.4 μg g(-1)) and the mouth of Chabahar Bay (3.43±1.31 and 13.5±3.23 μg g(-1)), respectively. There was significant difference (P<0.05) of EPO plasma levels between Konarak, Beris and Ramin stations with the mouth of Chabahar Bay as the cleanest station. Reduction of Bowman's space, occlusion of the tubule lumen, leukocytes infiltration, melanomacrophage centers aggregation, nuclear vacuolation, nuclei hypertrophy of tubule cells, necrosis of the tubules, lifting of the tubular basement membrane and dilatation of glomerular capillaries were the most alterations observed in the kidney. The HAI values of Epaulet grouper from Konarak, Beris and Ramin stations were significantly higher than other stations (P<0.05). It was concluded that selected biomarkers as a first investigation could be useful tools to environmental biomonitoring programs.

High affinity of cadmium and copper to head kidney of common carp (Cyprinus carpio L.)

The aim of the present study was to evaluate bioaccumulation of metals in various tissues of the freshwater fish Cyprinus carpio L. exposed to cadmium and copper (a xenobiotic and a microelement). The fish were subjected to short-term (3 h, Cd-S and Cu-S) or long-term (4 weeks, Cd-L and Cu-L) exposures to 100 % 96hLC₅₀ or 10 % 96hLC₅₀, respectively. Blood, gill, liver, head and trunk kidney were isolated weekly from 5 fish of each group for 4 weeks (post-short-term exposure and during long-term exposure). Atomic absorption spectrophotometry technique was applied to measure concentrations of metals (Cd and Cu) in fish tissues. Initial concentrations of copper in fish tissues were higher than levels of cadmium. Cadmium and copper levels increased in all tissues of metal-exposed fish. After short-term exposures (at higher concentration) and during long-term exposures (at lower concentration), similar changes in metal concentrations were observed. The values of accumulation factor (ratio of final to initial metal concentration) were higher for cadmium as compared to copper. Comparison of metal levels and accumulation factors in various tissues revealed that cadmium and copper showed very high affinity to head kidney of common carp (higher than to other tissues), but accumulation factors for cadmium in trunk, head kidney and liver were much higher than for copper. The concentrations of copper in organs of Cu-exposed fish increased only slightly and quickly returned to the control level, which shows that fish organism easily buffered metal level. On the other hand, concentrations of cadmium considerably increased and remained elevated for a long time which suggests that activation of mechanisms of sequestration and elimination of cadmium required more time.

Differential effects of chronic hypoxia and feed restriction on the expression of leptin and its receptor, food intake regulation and the endocrine stress response in common carp

Appetite suppression is a common response to hypoxia in fish that confers significant energy savings. Yet little is known about the endocrine signals involved in the regulation of food intake during chronic hypoxia. Thus, we assessed the impact of chronic hypoxia on food intake, the expression of the potent anorexigenic signal leptin and its receptor (lepr), the mRNA levels of key hypothalamic appetite-regulating genes, and the activity of the hypothalamic–pituitary–interrenal (HPI) axis in common carp, Cyprinus carpio. Fish exposed to 10% O2 saturation for 8 days were chronically anorexic and consumed on average 79% less food than normoxic controls. Hypoxia also elicited gradual and parallel increases in the expression of liver leptin-a-I, leptin-a-II, lepr and erythropoietin, a known hypoxia-responsive gene. In contrast, the liver mRNA levels of all four genes remained unchanged in normoxic fish pair-fed to the hypoxia treatment. In the hypothalamus, expression of the appetite-regulating genes were consistent with an inhibition and stimulation of hunger in the hypoxic and pair-fed fish, respectively, and reduced feed intake led to a decrease in lepr. Although both treatments elicited similar delayed increases in plasma cortisol, they were characterized by distinct HPI axis effector transcript levels and a marked differential increase in pituitary lepr expression. Together, these results show that a reduction in O2 availability, and not feed intake, stimulates liver leptin-a expression in common carp and suggest that this pleiotropic cytokine is involved in the regulation of appetite and the endocrine stress response during chronic hypoxia.

Effects of chronic nanoparticulate silver exposure to adult and juvenile sheepshead minnows (Cyprinodon variegatus)

The use of nanoparticulate silver (AgNP) is increasingly widespread and recently has been shown to have a plausible release route into aquatic environments. To date, relatively little research has examined the effects of AgNP on estuarine fish. The authors present data indicating that chronic exposure to low levels of AgNP induces significant adverse effects in both juvenile and adult sheepshead minnows (Cyprinodon variegarus; SHMs). Chronic exposure to low levels of AgNP produced significant increases in tissue burdens in both juvenile and adult SHMs, resulting in significant thickening of epithelia gill tissue and in dramatically altered gene expression profiles. The results do not appear to be attributable to the release of silver ions through particle dissolution. The alteration in gene expression was greatest in adult gonads, but no evidence of AgNP-related dysfunction was found at the tissue level. In contrast, the authors found a significant effect on gill morphology, but very little evidence of effect on gill transcription profiles.

Parental hypoxic exposure confers offspring hypoxia resistance in zebrafish (Danio rerio)

Maternal influences are a potentially important component of transgenerational transfer of phenotype in vertebrates. This study on zebrafish (Danio rerio) examined how chronic hypoxic exposure on adults affected the phenotype of their offspring. Separate adult populations were exposed to hypoxia (13.1 kPa O2) or normoxia (21.1 kPa O2) for periods ranging from 1 to 12 weeks. Adults were then returned to normoxia and bred within experimental groups. Adult fecundity and egg characteristics (volume of egg, yolk and perivitelline fluid) were assessed. Subsequently, larval body length, time to loss of equilibrium in severe hypoxia (~4 kPa O2), and critical thermal minima (CTMin) and maxima (CTMax) were measured at 6, 9, 12, 15, 18, 21 and 60 days post fertilization (dpf). Adult fecundity was depressed by hypoxic exposure. Egg component volumes were also depressed in adults exposed to 1-2 weeks of hypoxia, but returned to control levels following longer hypoxic exposure. Adult hypoxic exposures of &gt;1 week resulted in longer body lengths in their larval offspring. Time to loss of equilibrium in severe hypoxia (i.e. hypoxic resistance) in control larvae decreased from 6 to 12 dpf, remaining constant thereafter. Notably, hypoxic resistance from 6-18 dpf was ~15% lower in larvae whose parents were exposed to just 1 week of chronic hypoxia, but resistance was significantly increased by ~24-30% in 6-18 dpf in larvae from adults exposed to 2, 3 or 4 weeks of hypoxia. CTMin (~39.5°C) and CTMax (~10-12 °C) were unchanged by parental hypoxic exposure. This study demonstrates that parental hypoxic exposure in adult zebrafish has profound epigenetic effects on the morphological and physiological phenotype of their offspring.