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 (ΣPAH= 4.

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.

Exposure and Recovery from Environmentally Relevant Levels of Waterborne Polycyclic Aromatic Hydrocarbons from Deepwater Horizon Oil: Effects on the Gulf Toadfish Stress Axis.

There is evidence that the combination of polycyclic aromatic hydrocarbons (PAHs) released in the Deepwater Horizon oil spill impairs the glucocorticoid stress response of vertebrates in the Gulf of Mexico, but the mechanisms are unclear. We hypothesized that inhibition of cortisol release may be due to 1) overstimulation of the hypothalamic-pituitary-inter-renal (HPI) axis, or 2) an inhibition of cortisol biosynthesis through PAH activation of the aryl hydrocarbon receptor (AhR). Using a flow-through system, Gulf toadfish (Opsanus beta) were continuously exposed to control conditions or one of 3 environmentally relevant concentrations of PAHs from Deepwater Horizon oil (∑PAH  = 0-3 μg L ) for up to 7 d.

Evidence that Gulf toadfish use pulsatile urea excretion to communicate social status.

Gulf toadfish (Opsanus beta), a highly territorial marine teleost species, are believed to communicate through chemicals released across the gill during pulsatile urea excretion. While freshwater teleost and crustacean urinary signals have been shown to relay information about dominance to reduce physical aggression in future encounters, the use of chemical signals to convey social status in marine teleosts is understudied. Behavior and urea excretion patterns were monitored in pairs of male toadfish during an initial agonistic encounter and in a 2 encounter where a subset of pairs had their nares blocked to determine how olfaction, and thus chemical communication, play a role in establishing dominance.

Impacts of a local music festival on fish stress hormone levels and the adjacent underwater soundscape.

An understudied consequence of coastal urbanization on marine environments is sound pollution. While underwater anthropogenic sounds are recognized as a threat to aquatic organisms, little is known about the effects of above-surface coastal sound pollution on adjacent underwater soundscapes and the organisms inhabiting them. Here, the impact of noise from the 2019 Ultra Music Festival® in Miami, FL, USA was assessed at the University of Miami Experimental Hatchery (UMEH) located directly adjacent to the music festival and on underwater sound levels in Bear Cut, a nearby water channel.

Do reproductive hormones control Gulf toadfish pulsatile urea excretion?

Gulf toadfish (Opsanus beta) can excrete the majority of their nitrogenous waste as urea in distinct pulses across their gill. Urea pulses are controlled by cortisol and serotonin (5-HT) and are believed to contain chemical signals that may communicate reproductive and/or social status. The objectives of this study were to determine if reproductive hormones are involved in controlling pulsatile urea excretion, and if toadfish respond to prostaglandins as a chemical signal.

Pulsatile urea excretion in Gulf toadfish: the role of circulating serotonin and additional 5-HT receptor subtypes.

The neurochemical serotonin (5-HT) is involved in stimulating pulsatile urea excretion in Gulf toadfish (Opsanus beta) through the 5-HT receptor; however, it is not known if (1) the 5-HT signal originates from circulation or if (2) additional 5-HT receptor subtypes are involved. The first objective was to test whether 5-HT may be acting as a hormone in the control of pulsatile urea excretion by measuring potential fluctuations in circulating 5-HT corresponding with a urea pulse, which would suggest circulating 5-HT may be involved with urea pulse activation. We found that plasma 5-HT significantly decreased by 38% 1 h after pulse detection when branchial urea excretion was significantly elevated and then returned to baseline.

Do Gulf Toadfish Use Pulsatile Urea Excretion to Chemically Communicate Reproductive Status?

Gulf toadfish (Opsanus beta) are exceptionally capable of switching from excreting ammonia as their primary nitrogenous waste to excreting predominantly urea in distinct pulses across the gill. Previous studies suggest that these urea pulses may be used for intraspecific chemical communication. To determine whether pulsatile urea excretion communicates reproductive status, toadfish were sexed using ultrasound and delivered conspecific-conditioned seawater (CC-SW) that previously housed a conspecific of the opposite sex, a conspecific chemical alarm cue (avoidance control), or a prey cue (attraction control).

Extrinsic nerves are not involved in branchial 5-HT dynamics or pulsatile urea excretion in Gulf toadfish, Opsanus beta.

Gulf toadfish (Opsanus beta) can switch from continuously excreting ammonia as their primary nitrogenous waste to excreting predominantly urea in distinct pulses. Previous studies have shown that the neurotransmitter serotonin (5-HT) is involved in controlling this process, but it is unknown if 5-HT availability is under central nervous control or if the 5-HT signal originates from a peripheral source. Following up on a previous study, cranial nerves IX (glossopharyngeal) and X (vagus) were sectioned to further characterize their role in controlling pulsatile urea excretion and 5-HT release within the gill.

Crowding stress inhibits serotonin 1A receptor-mediated increases in corticotropin-releasing factor mRNA expression and adrenocorticotropin hormone secretion in the Gulf toadfish.

Stimulation of the serotonin 1A (5-HT1A) receptor subtype by 5-HT has been shown to result in an elevation in plasma corticosteroid levels in both mammals and several species of teleost fish, including the Gulf toadfish (Opsanus beta); however, in the case of teleost fish, it is not clearly known at which level of the hypothalamic-pituitary-interrenal axis the 5-HT1A receptor is stimulated. Additionally, previous investigations have revealed that chronic elevations of plasma cortisol mediate changes in brain 5-HT1A receptor mRNA and protein levels via the glucocorticoid receptor (GR); thus, we hypothesized that the function of centrally activated 5-HT1A receptors is reduced or abolished as a result of chronically elevated plasma cortisol levels and that this response is GR mediated. Our results are the first to demonstrate that intravenous injection of the 5-HT1A receptor agonist, 8-OH-DPAT, stimulates a significant increase in corticotropin-releasing factor (CRF) precursor mRNA expression in the hypothalamic region and the release of adrenocorticotropic hormone (ACTH) from the pituitary of teleost fish compared to saline-injected controls.