Opsanus Beta Research Articles

Gulf toadfish (Opsanus beta) urinary bladder ion and water transport is enhanced by acclimation to higher salinity to serve water balance.

Marine teleosts experience ion gain and water loss in their natural habitats. Among other tissues, the urinary bladder epithelium of marine fishes has been shown to actively transport ions to facilitate water absorption. However, transport properties of the urinary bladder epithelium of marine fishes and its plasticity in altered ambient salinities is relatively under-investigated. We describe urinary bladder epithelium electrophysiology, water flux, and expressions of ion transporters in urinary bladder tissue of Gulf toadfish (Opsanus beta) acclimated to either 35 ppt or 60 ppt seawater. Water absorption in bladder sac preparations increased ~ 350% upon acclimation to 60 ppt. Increases in water transport coincided with a significant ~ 137% increase in urinary bladder tissue mucosal-to-serosal short circuit current (Isc) and a ~ 56% decrease in tissue membrane resistance. Collectively, these metrics indicate that an active electrogenic system facilitates water absorption via Na+ (and Cl-) transport in urinary bladder tissue. Furthermore, pharmacological inhibition of urinary bladder tissue Isc and expression of a suite of ion transporters and channels previously unidentified in this tissue provide mechanistic insights into the transport processes responsible for water flux. Analysis of water transport to overall Gulf toadfish water balance reveals a modest water conservation role for the urinary bladder of ~ 0.5% of total water absorption in 35 ppt and 1.9% in 60 ppt acclimated toadfish. These results emphasize that electrogenic ion transport facilitates water-absorptive properties of the urinary bladder in Gulf toadfish - a process that is regulated to facilitate water homeostasis.

Long-read de novo genome assembly of Gulf toadfish (Opsanus beta)

BackgroundThe family Batrachoididae are a group of ecologically important teleost fishes with unique life histories, behavior, and physiology that has made them popular model organisms. Batrachoididae remain understudied in the realm of genomics, with only four reference genome assemblies available for the family, with three being highly fragmented and not up to current assembly standards. Among these is the Gulf toadfish, Opsanus beta, a model organism for serotonin physiology which has recently been bred in captivity.ResultsHere we present a new, de novo genome and transcriptome assemblies for the Gulf toadfish using PacBio long read technology. The genome size of the final assembly is 2.1 gigabases, which is among the largest teleost genomes. This new assembly improves significantly upon the currently available reference for Opsanus beta with a final scaffold count of 62, of which 23 are chromosome scale, an N50 of 98,402,768, and a BUSCO completeness score of 97.3%. Annotation with ab initio and transcriptome-based methods generated 41,076 gene models. The genome is highly repetitive, with ~ 70% of the genome composed of simple repeats and transposable elements. Satellite DNA analysis identified potential telomeric and centromeric regions.ConclusionsThis improved assembly represents a valuable resource for future research using this important model organism and to teleost genomics more broadly.

Gulf Toadfish (Opsanus beta) Boatwhistle Calls—A Prevalent Acoustic Cue with Passive Acoustic Monitoring Applications

Gulf Toadfish (Opsanus beta) Boatwhistle Calls—A Prevalent Acoustic Cue with Passive Acoustic Monitoring Applications

Gulf toadfish (Opsanus beta) gill neuroepithelial cells in response to hypoxia exposure.

Neuroepithelial cells (NECs) within the fish gill contain the monoamine neurochemical serotonin (5-HT), sense changes in the partial pressure of oxygen (PO2) in the surrounding water and blood, and initiate the cardiovascular and ventilatory responses to hypoxia. The distribution of neuroepithelial cells (NECs) within the gill is known for some fish species but not for the Gulf toadfish, Opsanus beta, a fish that has always been considered hypoxia tolerant. Furthermore, whether NEC size, number, or distribution changes after chronic exposure to hypoxia, has never been tested. We hypothesize that toadfish NECs will respond to hypoxia with an increase in NEC size, number, and a change in distribution. Juvenile toadfish (N = 24) were exposed to either normoxia (21.4 ± 0.0kPa), mild hypoxia (10.2 ± 0.3kPa), or severe hypoxia (3.1 ± 0.2kPa) for 7 days and NEC size, number, and distribution for each O2 regime were measured. Under normoxic conditions, juvenile toadfish have similar NEC size, number, and distribution as other fish species with NECs along their filaments but not throughout the lamellae. The distribution of NECs did not change with hypoxia exposure. Mild hypoxia exposure had no effect on NEC size or number, but fish exposed to severe hypoxia had a higher NEC density (# per mm filament) compared to mild hypoxia-exposed fish. Fish exposed to severe hypoxia also had longer gill filament lengths that could not be explained by body weight. These results point to signs of phenotypic plasticity in these juvenile, lab-bred fish with no previous exposure to hypoxia and a strategy to deal with hypoxia exposure that differs in toadfish compared to other fish.

Influence of environmental factors on reproduction of the invasive Gulf toadfish Opsanus beta (Teleostei: Batrachoididae) in a subtropical estuary

A hallmark of biological invasion is the rapid reproduction of invasive species. However, we still do not have an adequate understanding of how fluctuations in environmental factors affect the reproduction of invasive species, particularly in estuarine habitats. In this study, we evaluated the reproduction of the Gulf toadfish Opsanus beta and its relationships with temperature and rainfall in the Paranaguá estuary, a subtropical region in southern Brazil. This species was likely introduced into the Brazilian ecosystems through the discharge of ballast water. Since invasion, which was first reported in port areas, the species has rapidly spread along the Brazilian coast line. We collected specimens monthly from October 2011 to September 2012 and from October 2019 to September 2020, to give us insight into the seasonal and temporal changes in the reproduction of this species. We found that O. beta population uses the estuary throughout its life cycle, including during spawning. Females and males spawned throughout almost the entire sampling period and spawning was specified as partially. Peak reproductive activity occurred in periods of lower temperature and was also related to rain. The length of first maturation in females (10cm) was considered early, indicating reproductive activity in smaller individuals. Our results demonstrate that the reproductive strategy used by the invasive species supports its ability to successfully colonize new environments.

Plastic, It's What's for Dinner: A Preliminary Comparison of Ingested Particles in Bottlenose Dolphins and Their Prey.

Microplastic ingestion was reported for common bottlenose dolphins (Tursiops truncatus) inhabiting Sarasota Bay, FL, USA, a community that also has prevalent exposure to plasticizers (i.e., phthalates) at concentrations higher than human reference populations. Exposure sources are currently unknown, but plastic-contaminated prey could be a vector. To explore the potential for trophic exposure, prey fish muscle and gastrointestinal tract (GIT) tissues and contents were screened for suspected microplastics, and particle properties (e.g., color, shape, surface texture) were compared with those observed in gastric samples from free-ranging dolphins. Twenty-nine fish across four species (hardhead catfish, Ariopsis felis; pigfish, Orthopristis chrysoptera; pinfish, Lagodon rhomboides; and Gulf toadfish, Opsanus beta) were collected from Sarasota Bay during September 2022. Overall, 97% of fish (n = 28) had suspected microplastics, and GIT abundance was higher than muscle. Fish and dolphin samples contained fibers and films; however, foams were common in dolphin samples and not observed in fish. Suspected tire wear particles (TWPs) were not in dolphin samples, but 23.1% and 32.0% of fish muscle and GIT samples, respectively, contained at least one suspected TWP. While some similarities in particles were shared between dolphins and fish, small sample sizes and incongruent findings for foams and TWPs suggest further investigation is warranted to understand trophic transfer potential.

The Gulf toadfish goes south: assessing the potential habitat suitability of Opsanus beta in response to climate change

Climate change can directly influence invasive species range, and may reflect in greater habitat suitability, consequently increasing losses in native biodiversity. Habitat suitability modelling can help identify priority areas for conservation and rapid response for invasive taxa. This study aimed to model the habitat suitability of Opsanus beta, an invasive fish species, in South America under current and future climate change scenarios. Three modelling techniques, Generalized Linear Model (GLM), Maximum Entropy Algorithm (Maxent), and Random Forest (RF), were applied, and their results were compared and then put together in an Ensemble model to visualize habitat suitability. We found that the current habitat suitability of O. beta in South America is relatively low, with its occurrences mostly related to coastal port areas, suggesting that the species was introduced from ballast water. The increase in mean temperature at mean depth and temperature range were the most relevant variables influencing the species habitat suitability. The gradual increase in habitat suitability for the 2100 climate change scenarios, particularly in more severe climate change scenarios, such as the RCP 8.5, was also observed. The study highlights the critical need to use habitat suitability models to mitigate the impact of future climate change scenarios on invasive species. The findings call for preventive measures to be taken in time to prepare areas that may become the target of dispersal and establishment of O. beta.

A large aerobic scope and complex regulatory abilities confer hypoxia tolerance in larval toadfish, Opsanus beta, across a wide thermal range

Few studies have been performed on early-life stage toadfish, and none have addressed their tolerance to temperature and hypoxia despite large seasonal temperature fluctuations and daily hypoxia in their natural environment. The first directed captive breeding of Opsanus beta allowed the examination of larval oxygen demands and hypoxia tolerance across the range of their environmental temperatures (23–33 °C). Larval toadfish exhibited a surprisingly large aerobic scope across the tested temperature range. In response to progressive hypoxia, larval toadfish showed early metabolic depression and a low regulation index (RI), while juveniles had higher regulatory abilities but, unexpectedly, a lower aerobic scope. Larval and juvenile toadfish survived hours of severe hypoxia, but larval fish had a higher excessive post-hypoxia oxygen consumption, yet their metabolic rate returned to RMR in the same timeframe as the juveniles, likely due to their higher aerobic scope. We defined hypoxia tolerance using a physiological trait, p50, the oxygen tension in which oxygen uptake is reduced to 50 % of the metabolic rate at rest and determined it at all tested temperatures. Comparing these p50 values to environmental conditions in Florida Bay using hourly temperature and oxygen measurements from January 2014–October 2021 revealed that larval toadfish rarely experience < p50 conditions (11 % of events). Further, the median duration of these events was 3 h. The metabolic performance of larval toadfish combined with temperature and oxygen observations from their natural environment reveals the fascinating strategy in which larval toadfish survive diel hypoxia across seasons.

Metabolic cost of osmoregulation by the gastro-intestinal tract in marine teleost fish.

Introduction: Although dozens of studies have attempted to determine the metabolic cost of osmoregulation, mainly by comparing standard metabolic rates (SMR) in fish acclimated to different salinities, consensus is still lacking. Methods: In the present study, using the Gulf toadfish, Opsanus beta, we aimed to determine the metabolic cost of esophageal and intestinal osmoregulatory processes by estimating ATP consumption from known ion transport rates and pathways and comparing these estimates with measurements on isolated tissues. Further, we performed whole animal respirometry on fish acclimated to 9, 34 and 60ppt. Results and Discussion: Our theoretical estimates of esophageal and intestinal osmoregulatory costs were in close agreement with direct measurements on isolated tissues and suggest that osmoregulation by these tissues amounts to ∼2.5% of SMR. This value agrees well with an earlier attempt to estimate osmoregulation cost from ion transport rates and combined with published measurements of gill osmoregulatory costs suggests that whole animal costs of osmoregulation in marine teleosts is ∼7.5% of SMR. As in many previous studies, our whole animal measurements were variable between fish and did not seem suited to determine osmoregulatory costs. While the esophagus showed constant metabolic rate regardless of acclimation salinity, the intestine of fish acclimated to higher salinities showed elevated metabolic rates. The esophagus and the intestine had 2.1 and 3.2-fold higher metabolic rates than corresponding whole animal mass specific rates, respectively. The intestinal tissue displays at least four different Cl- uptake pathways of which the Na+:Cl-:2K+ (NKCC) pathway accounts for 95% of the Cl- uptake and is the most energy efficient. The remaining pathways are via apical anion exchange and seem to primarily serve luminal alkalinization and the formation of intestinal CaCO3 which is essential for water absorption.

A multi-targeted investigation of Deepwater Horizon crude oil exposure impacts on the marine teleost stress axis

The toxicity of the polycyclic aromatic hydrocarbons (PAHs) in Deepwater Horizon (DWH) oil is well-established, but a knowledge gap exists regarding how this combination of PAHs affects the vertebrate stress axis. We hypothesized that (1) marine vertebrates exposed to DWH PAHs experience stress axis impairment, and co-exposure to an additional chronic stressor may exacerbate these effects, (2) serotonin (5-hydroxytryptamine; 5-HT) may act as a secondary cortisol secretagogue in DWH PAH-exposed fish to compensate for impairment, and (3) the mechanism of stress axis impairment may involve downregulation of cyclic adenosine monophosphate (cAMP; as proxy for melanocortin 2 receptor (MC2R) functionality), total cholesterol, and/or mRNA expression of CYP1A and steroidogenic proteins StAR, P450scc, and 11β-h at the level of the kidney. We found that in vivo plasma cortisol and plasma adrenocorticotropic hormone (ACTH) concentrations in Gulf toadfish exposed to an environmentally relevant DWH PAH concentration (ΣPAH50= 4.6 ± 1.6 μg/L) for 7 days were not significantly different from controls, whether fish were chronically stressed or not. However, the rate of cortisol secretion by isolated kidneys after acute stimulation with ACTH was significantly lower in PAH-exposed toadfish compared to clean seawater (SW) controls. 5-HT does not appear to be acting as a secondary cortisol secretagogue, rather, PAH-exposed + stressed toadfish exhibited significantly lower plasma 5-HT concentrations than clean SW + stressed fish as well as a reduced sensitivity to 5-HT at the level of the kidney. There was a tendency for kidney cAMP concentrations to be lower in PAH-exposed fish (p = 0.069); however, mRNA expression of steroidogenic proteins between control and PAH-exposed toadfish were not significantly different and a significant elevation in total cholesterol concentration in PAH-exposed toadfish compared to controls was measured. Future work is needed to establish whether the slower cortisol secretion rate by isolated kidneys of PAH-exposed fish is detrimental, to determine the potential role of other secretagogues in compensating for the impaired kidney interrenal cell function, and to determine whether there is a reduction in MC2R mRNA expression or an impairment in the function of steroidogenic proteins.

Inferring ecological connectivity between populations of Opsanus beta (Goode &amp; Bean, 1880) from the southern Gulf of Mexico and the South-western Atlantic coast

AbstractOtoliths are an excellent tool in studies on ecological connectivity of fish species populations. Opsanus beta is an invasive species introduced on the Brazilian coast, but not native from the Gulf of Mexico. The present study aimed to compare the otolith contours of specimens collected in Mexico (Celestún, CEL) and in two Brazilian estuaries (Santos Bay, STB, and Paranaguá Estuarine Complex, PEC). In the laboratory, 99 otoliths were extracted, photographed and compared using wavelet analysis. The otolith contours varied between sites (39 from CEL, 26 from STB and 34 from PEC). The linear discriminant analysis correctly reclassified 87.9% of otoliths by sites, with the best reclassifications in the CEL (97.36%), followed by PEC (88.23%) and SBT (73.07%). MANOVA showed significant differences in otolith contours between sites (F = 5.37; P &lt; 0.005). The otolith contour from CEL was significantly different from those from the PEC and SBT. However, the otolith contour of the two Brazilian estuaries did not significantly differ among them (MANOVA, P &gt; 0.005). Our results indicate O. beta populations on the Brazilian coast are connected, and probably isolated from the Mexican population.

Deoxygenated toadfish turn up gill serotonin degradation to catch breath

Serotonin is probably most famed for its mood-altering role in the human brain. Yet, long before people began taking serotonin reuptake inhibitors to treat depression, the versatile neurotransmitter was known to cause blood vessels to constrict, which could be a problem for fish when oxygen levels in water plummet naturally. ‘Toadfish slow their heart rate, lower their blood pressure and breathe deeper when oxygen drops. These responses help maximize their oxygen absorption and usage’, says John Sebastiani from the University of Miami, USA. Knowing that the levels of serotonin in the blood are tightly maintained by a delicate balance between tissue absorption and destruction and excretion, Sebastiani, Allyson Sabatelli and Danielle McDonald, also from the University of Miami, decided to investigate how Gulf toadfish (Opsanus beta) manage serotonin levels in their blood when their oxygen supply drops a little.‘Toadfish are lazy and like to settle on the bottom, so it's pretty common for them to be accidentally caught in shrimping boat nets’, says Sebastiani, explaining that fishermen just throw them back. ‘As long as we have buckets of seawater and an air pump, we can collect the fish and safely transport them back to campus’, he adds. After returning to the lab, the team reduced the oxygen in the fish's water from 100% to 50% – which isn't too extreme for the fish – for 2 min, 40 min and 24 h respectively, before collecting samples of the fish's brains, gills, liver, kidneys and heart, as well as their bile and urine to monitor their ability to absorb serotonin and break it down.Checking the amount of serotonin circulating in the fish's blood, the team found that levels in the fish that experienced 40 min of lower oxygen had fallen by 34%, while the fish that had spent a whole day in reduced oxygen experienced a 54% drop. However, when the researchers checked which tissues were absorbing and destroying serotonin, they were surprised that the heart had reduced how much serotonin it was breaking down – potentially supplying the gills with more of the blood vessel constricting neurotransmitter, instead of removing it from the blood to dilate the gill blood vessels and allow them to absorb more oxygen from the depleted water. But the researchers had recorded that serotonin levels in the blood declined, so which other tissue was removing the neurotransmitter from the fish's blood?Next, the team measured serotonin breakdown in the gill when the fish experienced periods of reduced oxygen, and the level increased threefold. ‘These results suggest that serotonin clearance is upregulated during hypoxia and likely driven, in part, by mechanisms within the gill’, says Sebastiani.In addition, when measuring the quantity of serotonin being excreted in the bile produced by the liver, the researchers discovered that the neurotransmitter levels almost doubled after they replaced the fish's well-oxygenated water with poorly oxygenated water for 40 min. As well as breaking the neurotransmitter down, the fish also excrete it. However, the team points out that serotonin production in the liver, which is a major source of the neurotransmitter, could reduce when the fish experience a fall in oxygen, and they are curious to find out more about how serotonin impacts the fish's heart function when their oxygen supply dwindles.

Mild hypoxia exposure impacts peripheral serotonin uptake and degradation in Gulf toadfish (Opsanus beta).

Plasma serotonin (5-hydroxytryptamine, 5-HT) homeostasis is maintained through the combined processes of uptake (via the 5-HT transporter SERT, and others), degradation (via monoamine oxidase, MAO) and excretion. Previous studies have shown that inhibiting SERT, which would inhibit 5-HT uptake and degradation, attenuates parts of the cardiovascular hypoxia reflex in gulf toadfish (Opsanus beta), suggesting that these 5-HT clearance processes may be important during hypoxia exposure. Therefore, the goal of this experiment was to determine the effects of mild hypoxia on 5-HT uptake and degradation in the peripheral tissues of toadfish. We hypothesized that 5-HT uptake and degradation would be upregulated during hypoxia, resulting in lower plasma 5-HT, with uptake occurring in the gill, heart, liver and kidney. Fish were exposed to normoxia (97.6% O2 saturation, 155.6 Torr) or 2min, 40min or 24 h mild hypoxia (50% O2 saturation, ∼80 Torr), then injected with radiolabeled [3H]5-HT before blood, urine, bile and tissues were sampled. Plasma 5-HT levels were reduced by 40% after 40 min of hypoxia exposure and persisted through 24 h. 5-HT uptake by the gill was upregulated following 2 min of hypoxia exposure, and degradation in the gill was upregulated at 40 min and 24 h. Interestingly, there was no change in 5-HT uptake by the heart and degradation in the heart decreased by 58% within 2 min of hypoxia exposure and by 85% at 24 h. These results suggest that 5-HT clearance is upregulated during hypoxia and is likely driven, in part, by mechanisms within the gill and not the heart.

Altered acoustic community structure indicates delayed recovery following ecosystem perturbations

In the Anthropocene, there is an intensification of ecological disturbances that can be directly or indirectly attributed to human activities. Seagrass meadows are among the most imperiled ecosystems worldwide and are particularly sensitive to anthropogenic disturbance events. In Everglades National Park, Florida, USA, ecological disturbances including widespread seagrass die offs, can in part be attributed to anthropogenic alteration of historic freshwater flow. In this study, we assess the impacts of seagrass die offs on the composition and behavior of aquatic organisms in acoustic communities at two ecologically similar sites in Florida Bay: Buoy Key, which experienced massive seagrass die off in 2015, and Little Rabbit Key, which did not. We focused on three sonic indicator species for North American estuaries and coastal ecosystems, and specifically Florida Bay: spotted seatrout (Cynoscion nebulosus, family Sciaenidae), gulf toadfish (Opsanus beta, family Batrachoididae), and snapping shrimp (Alpheus spp. and Synalpheus spp., family Alpheidae). The sounds produced by these species are collectively indicative of a broader range of ecosystem function and services – including trophic transfer and recreational fishing – and are more indicative of ecosystem functioning at varying temporal scales than any one species alone. Using a combination of automated detection and visual spectrographic analysis on passive acoustic data, we found that the occurrence of seatrout and toadfish calls and/or chorusing were significantly lower at the disturbed site than the undisturbed site, with no seatrout or toadfish breeding choruses detected at the disturbed location. At both sites, toadfish call properties exhibited a direct relationship with water temperature. Snapping shrimp snap rates were significantly lower at the disturbed site, and snap rates were positively related to temperature at the undisturbed location. Further, examination of a short-duration, pre-disturbance acoustic dataset, showed minimal differences in the acoustic occurrence of the three species at the disturbed site between 2015 immediately after the die off and 2018. These results support the hypothesis that by 2018 the disturbed site had not fully recovered from the most recent seagrass die off and that restoration efforts may still needed. Acoustic community composition and behavior may be used as a reliable indicator of ecosystem health and restoration success or efficacy. This work lays the conceptual groundwork for using acoustic communities as indicators in human altered systems to inform managers that habitats either may be approaching disturbance or may require continued restoration efforts to meet achieve recovery goals.

Is serotonin uptake by peripheral tissues sensitive to hypoxia exposure?

In the Gulf toadfish (Opsanus beta), the serotonin (5-HT) transporter (SERT) is highly expressed in the heart, and the heart and gill both demonstrate the capacity for SERT-mediated uptake of 5-HT from the circulation. Because 5-HT is a potent vasoconstrictor in fish, we hypothesized that hypoxia exposure may increase 5-HT uptake by these tissues-and increase excretion of 5-HT-to prevent branchial vasoconstriction that would hamper gas exchange. Spot sampling of blood, bile, and urine revealed that fish exposed to chronic hypoxia (1.83 ± 0.12mg·L-1 O2 for 24-26h) had 41% lower plasma 5-HT in the ventral aorta (immediately following the heart) than in the hepatic vein (immediately before the heart), suggesting enhanced cardiac 5-HT uptake during hypoxia. 5-HT concentrations in the bile were greater than those in the urine, but there were no effects of acute (1.31 ± 0.06mg·L-1 O2 for 25min) or chronic hypoxia on 5-HT levels in these fluids. In 5-HT radiotracer experiments, the presence of tracer in the bile decreased upon hypoxia exposure, but, surprisingly, neither acute nor chronic hypoxia-induced changes in [3H]5-HT uptake in the heart, gill, or other tissues. Given the likely impact of the hypoxia exposure on metabolic rate, future studies should examine the effects of a milder hypoxia exposure on 5-HT uptake into these tissues and the role of 5-HT degradation.

Citizen science as a tool for understanding the silent dispersion of toadfish Opsanus beta (Goode and Bean, 1880).

Citizen science is an excellent tool in studies of the spatial distribution of non-native species. In Brazil, Opsanus beta has recently been introduced. Studies indicate the occurrence of this species in five estuaries off the Brazilian coast (Guanabara Bay, Sepetiba Bay, Santos Bay, Paranaguá Estuarine Complex and Guaratuba Bay). The present study aims to understand the dispersion of this species on the Brazilian coast through citizen science. Between January and May 2021, information about O. beta was weekly posted in 32 recreational fishing Facebook groups. Sixty-five fishers reported catches of O. beta in estuaries (Guanabara Bay, Sepetiba Bay, Santos Bay and Paranaguá Estuarine Complex). In addition, there were reports from other shallow areas outside adjacent estuaries (Bertioga and Peruíbe, in Sao Paulo State) and the first occurrence record for Laguna (Santa Catarina State), a southern estuarine zone (28° 29' 45″ S to 48° 45' 36″ W). In four estuaries along the Brazilian coast where O. beta was recorded, there are internal ports that trade with countries from the Gulf of Mexico and Caribbean Sea (species original range), indicating ballast water as a possible introduction route. In Laguna, the introduction may have occurred by maritime cabotage services. The reproductive capacity, the aquarists' interest, the absence of introduction policies aimed at this species and the cabotage fleet transportation may be factors that help further extend the dispersal of O. beta on the Brazilian coast.

Age, growth, and ontogenetic variation in the sagitta otolith of Opsanus beta (Goode &amp; Bean, 1880), a non-native species in a wetland of international importance

Invasive species are among the most important problems for biodiversity conservation worldwide, particularly in megadiverse countries such as Brazil. However, there is no biological information to develop policies for managing invasive species populations in many cases. The life history parameters and otolith variations are essential to understanding the adaptations of the species introduced in marine environments. This study aimed to identify the age structure and ontogenetic variation in the sagitta otolith of Opsanus beta. Fish samples were obtained monthly in the Paranaguá Estuarine Complex (PEC), south of Brazil. The shape indices verified ontogenetic variations in the otoliths (PERMANOVA; F = 110; P &lt; 0.0001), but no sexual variations were observed in the shape of the otoliths (PERMANOVA; F = 3.65; P &gt; 0.05). Specimen aged between 1 to 9 years were observed in the PEC, with the highest occurrence of individuals between 3 and 6 years (78%). No sexual differences were observed between the ages by the Kimura test. Our results confirm that the O. beta population is well established with age groups similar to that observed in the region where the species is native.

Magnesium transport in the aglomerular kidney of the Gulf toadfish (Opsanus beta).

Despite having an aglomerular kidney, Gulf toadfish can survive in water ranging from nearly fresh up to 70 parts per thousand salinity. In hyperosmotic environments, the major renal function is to balance the passive Mg2+ load from the environment with an equal excretion. However, the molecular transporters involved in Mg2+ secretion are poorly understood. We investigated whether environmental MgCl2 alone or in combination with elevated salinity affected transcriptional regulation of genes classically involved in renal Mg2+ secretion (slc41a1, slc41a3, cnnm3) together with three novel genes (trpm6, trpm7, claudin-19) and two isoforms of the Na+/K+-ATPase α-subunit (nka-α1a, nka-α1b). First, toadfish were acclimated to 5, 9, 35, or 60 ppt water (corresponding to ~ 7, 13, 50 and 108mmolL-1 ambient [Mg2+], respectively) and sampled at 24h or 9days. Next, the impact of elevated ambient [Mg2+] was explored by exposing toadfish to control (50mmolL-1 Mg2+), or elevated [Mg2+] (100mmolL-1) at a constant salinity for 7days. Mg2+ levels in this experiment corresponded with levels in control and hypersaline conditions in the first experiment. A salinity increase from 5 to 60 ppt stimulated the level of all investigated transcripts in the kidney. In Mg2+-exposed fish, we observed a 14-fold increase in the volume of intestinal fluids and elevated plasma osmolality and [Mg2+], suggesting osmoregulatory challenges. However, none of the renal gene targets changed expression compared with the control group. We conclude that transcriptional regulation of renal Mg2+ transporters is induced by elevated [Mg2+] in combination with salinity rather than elevated ambient [Mg2+] alone.

The role of uptake and degradation in the regulation of peripheral serotonin dynamics in Gulf toadfish, Opsanus beta

The neurotransmitter serotonin (5-hyroxytryptamine, 5-HT) is involved in a variety of peripheral processes. Arguably most notable is its role as a circulating vasoconstrictor in the plasma of vertebrates. Plasma 5-HT is maintained at constant levels under normal conditions through the processes of cellular uptake, degradation, and excretion, known collectively as clearance. However, the degree to which each individual component of clearance contributes to this whole animal response remains poorly understood. The goal of this experiment was to determine the extent to which transporter-mediated uptake and intracellular degradation contribute to 5-HT clearance in the model teleost Gulf toadfish (Opsanus beta). Fish that were treated with the 5-HT transport inhibitors fluoxetine, buproprion, and decynium-22 had 1.47-fold higher plasma 5-HT concentrations and a 40% decrease in clearance rate compared to control fish. In contrast, fish treated with the MAO inhibitor clorgyline had a 1.54-fold increase in plasma 5-HT with no change in clearance rate. The results show that transporter-mediated 5-HT uptake plays an important role in controlling circulating 5-HT and whole body 5-HT homeostasis.

Exposure and Recovery of the Gulf Toadfish (Opsanus beta) to Weathered Deepwater Horizon Slick Oil: Impacts on Liver and Blood Endpoints.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants that can be responsible for a variety of deleterious effects on organisms. These adverse outcomes are relatively well studied, but at concentrations rarely found in the environment. Among the documented effects of sublethal acute PAH exposure are reductions in osmoregulatory capacity and immune function, and changes in the function of critical metabolic organs such as the liver. Gulf toadfish (Opsanus beta) were exposed to control seawater (0.006 µg tPAH50 /L) or water accommodated fractions of Deepwater Horizon spill oil diluted to 3 flow-through exposure regimes (0.009, 0.059, and 2.82 µg tPAH50 /L) for 7 d, with a recovery period of equal duration. We hypothesized that these chronic exposures would induce the aryl hydrocarbon receptor (AhR)-mediated pathways and result in significant impacts on markers of osmoregulatory, immune, and metabolic function. We further hypothesized that measurable reversal of these impacts would be observed during the recovery period. Our results indicate that activation of cytochrome P 450 (CYP)1A1 was achieved during exposure and reversed during the recovery phase. The only significant deviations from controls measured were a reduction in plasma glucose in fish exposed to medium and high levels of PAH after 7 d of exposure and a reduction in plasma osmolality fish exposed to high levels of PAHs after 7 d of recovery, when CYP1A1 messenger (m)RNA levels had returned to control levels. Our study illustrates a disconnect between the activation of CYP1A1 in response to environmentally realistic PAHs concentrations and several physiological endpoints and supports the idea that the AhR might not be associated with mediating osmoregulatory, immune, and metabolic changes in Gulf toadfish. Environ Toxicol Chem 2021;40:1075-1086. © 2020 SETAC.