Responses of bay anchovy (Anchoa mitchilli) larvae under lethal and sublethal scenarios of crude oil exposure

Biochemical, molecular, and physiological assessments of crude oil dietary exposure in sub-adult red drum (Sciaenops ocellatus)

A 14-day exposure study in which sub-adult red drum (Sciaenops ocellatus) were fed a petroleum crude oil-treated pellet feed was conducted to assess the potential effects of ingesting an oil-contaminated food source. Though food consumption decreased, significant polycyclic aromatic hydrocarbons accumulated in the body and liver, which did not affect the body and liver's fatty acid composition. In the red drum given the crude oil-treated feed, a significant decrease in the RNA:DNA growth rate index was noted, while only subtle changes in body and liver lipid composition were seen. Differentially expressed gene analysis in the liver demonstrated a significant down-regulation of leptin and up-regulation of the aryl hydrocarbon receptor nuclear translocator-like protein 1. Gene ontology and Kyoto Encyclopedia of Genes and Genomes analyses indicated enrichment of terms and pathways associated with cholesterol biosynthesis and oxidative stress. Ingenuity Pathway Analysis further predicted activation of seven pathways associated with cholesterol biosynthesis. Measured oxidative stress biomarkers in the blood indicated decreased systemic antioxidants with increased lipid peroxidation. The results of this study suggest that dietary oil exposure alters the signaling of biological pathways critical in cholesterol biosynthesis and disruptions in systemic oxidative homeostasis.

Acute and Chronic Effects of Crude Oil Water-Accommodated Fractions on the Early Life Stages of Marine Medaka (Oryzias melastigma, McClelland, 1839)

Oil spill is a major marine environmental pollution issue. Research regarding the long-term effects of oil spills on the early life stage of marine fish is still limited. In this study, the potential adverse impact of crude oil from one oil spill accident which occurred in the Bohai Sea on the early life stages of marine medaka (Oryzias melastigma, McClelland, 1839) was evaluated. A 96-h acute test (larvae) and a 21-d chronic test (embryo-larvae) of water-accommodated fractions (WAFs) from crude oil were conducted, respectively. The results of the acute test showed that only the highest concentration of WAFs (100.00%) significantly affected the mortality of larvae (p < 0.01) and that the 96 h-LC₅₀ was 68.92% (4.11 mg·L^-1 expressed as total petroleum hydrocarbons (TPHs)). Larval heart demonstrated histopathological alterations in all WAF-exposed groups. The chronic test results showed that, except for larval mortality, the total hatching success (%)/hatching time of embryos in WAF treatments was not significantly different from those of the control group (p > 0.05), and no malformation was found in surviving larvae after 21 d of exposure. Nevertheless, the exposed embryos and larvae in the highest concentration of WAFs (60.00%) demonstrated significantly reduced heart rate (p < 0.05) and increased mortality (p < 0.01), respectively. Overall, our results indicated that both acute and chronic WAF exposures had adverse impacts on the survival of marine medaka. In the early life stages, the heart of the marine medaka was the most sensitive organ which showed both structural alteration and cardiac dysfunction.

A comprehensive petrochemical vulnerability index for marine fishes in the Gulf of Mexico

Oil and gas extraction activities occur across the globe, yet species-specific toxicological information on the biological and ecological impacts of exposure to petrochemicals is lacking for the vast majority of marine species. To help prioritize species for recovery, mitigation, and conservation in light of significant toxicological data gaps, a trait-based petrochemical vulnerability index was developed and applied to the more than 1700 marine fishes present across the entire Gulf of Mexico, including all known bony fishes, sharks, rays and chimaeras. Using life history and other traits related to likelihood of exposure, physiological sensitivity to exposure, and population resiliency, final calculated petrochemical vulnerability scores can be used to provide information on the relative sensitivity, or resilience, of marine fish populations across the Gulf of Mexico to oil and gas activities. Based on current knowledge of traits, marine fishes with the highest vulnerability scores primarily occur in areas of high petrochemical activity, are found at or near the surface, and have low reproductive turnover rates and/or highly specialized diet and habitat requirements. Relative population vulnerability scores for marine fishes can be improved with additional toxicokinetic studies, including those that account for the synergistic or additive effect of multiple stressors, as well as increased research on ecological and life history traits, especially for deep living species.

Morphological and cardiac alterations after crude oil exposure in the early-life stages of the tropical gar (Atractosteus tropicus)

Fish development can be affected by environmental pollutants such as crude oil (anthropogenic or natural sources), causing alterations especially in cardiac function and morphology. Most such studies have focused on saltwater species, whereas studies in freshwater fishes are scant. The objective of the current study was to evaluate the effects of crude oil exposure (as 0, 5, 10, 15, or 20% high-energy water accommodated fractions, HEWAF) on cardiac function and edema formation during two early periods of development (embryo and eleuteroembryo, 48 h each) individually using the tropical gar Atractosteus tropicus as a model. Embryos did not exhibit alterations in body mass, total length, condition factor, and cardiac function as a function of oil. In contrast, eleuteroembryos proved to be more sensitive and exhibited increased body mass, total length, and condition factor, decreased heart rate and phenotypic alterations such as cardiac dysmorphia (tubular hearts) and spine curvature at high concentrations of HEWAF. Moreover, edema formation was observed in both stages This study shows different functional responses of A. tropicus after crude oil exposure and provides useful information of the developmental impacts of these compounds on the early life stages of freshwater tropical fishes.

A review of the toxicology of oil in vertebrates: what we have learned following the Deepwater Horizon oil spill

In the wake of the Deepwater Horizon (DWH) oil spill, a number of government agencies, academic institutions, consultants, and nonprofit organizations conducted lab- and field-based research to understand the toxic effects of the oil. Lab testing was performed with a variety of fish, birds, turtles, and vertebrate cell lines (as well as invertebrates); field biologists conducted observations on fish, birds, turtles, and marine mammals; and epidemiologists carried out observational studies in humans. Eight years after the spill, scientists and resource managers held a workshop to summarize the similarities and differences in the effects of DWH oil on vertebrate taxa and to identify remaining gaps in our understanding of oil toxicity in wildlife and humans, building upon the cross-taxonomic synthesis initiated during the Natural Resource Damage Assessment. Across the studies, consistency was found in the types of toxic response observed in the different organisms. Impairment of stress responses and adrenal gland function, cardiotoxicity, immune system dysfunction, disruption of blood cells and their function, effects on locomotion, and oxidative damage were observed across taxa. This consistency suggests conservation in the mechanisms of action and disease pathogenesis. From a toxicological perspective, a logical progression of impacts was noted: from molecular and cellular effects that manifest as organ dysfunction, to systemic effects that compromise fitness, growth, reproductive potential, and survival. From a clinical perspective, adverse health effects from DWH oil spill exposure formed a suite of signs/symptomatic responses that at the highest doses/concentrations resulted in multi-organ system failure.

Effects of short-duration oil exposure on bay anchovy (Anchoa mitchilli) embryos and larvae: mortality, malformation, and foraging

The Deepwater Horizon oil spill highlighted the need to understand the effects of oil exposure on marine eggs and larvae. To determine how short-duration exposure impacts the survivability of early life stages of the bay anchovy, Anchoa mitchilli, embryos and larvae ≤ 3-days-post-hatch (dph) were exposed to high-energy water accommodated fractions of weathered crude oil for 2 or 6 h. Lethal and sublethal effects of short-duration oil exposure were observed, including crippling malformations and altered optimal swimming and foraging behavior of larvae without malformation. The probability of mortality for larvae exposed as embryos (37.37 and 77.31 µg L^-1 total polycyclic aromatic hydrocarbons or 'TPAH'), assessed 48 h after exposure, increased from 0.06 to 0.15 (2 h) and 0.10-0.23 (6 h) relative to unoiled controls. When exposed as 1-dph larvae (8.80-37.37 µg L^-1 TPAH) and assessed 24 h after exposure, the probabilities increased from 0.20 to 0.76 (2 h) and 0.28-0.99 (6 h). Among surviving larvae, probabilities of yolk-sac, finfold, notochord, and cranio-facial malformations increased with exposure concentration, duration, and time after exposure by up to 0.07 immediately following exposure of 1-dph larvae and 0.55 24 h after exposure. When assessed 48 h after exposure as embryos, the probability of larval malformation reached 0.43. First-feeding (3-dph) foraging behavior was altered immediately and 24 h after 2 h exposures (8.80-77.31 µg L^-1 TPAH). Time spent in motion and swim speed increased with exposure concentration by up to 331% and 189%, respectively. The number of bursts min^-1 increased by 293% immediately and 152% 24 h after exposure. Burst distance decreased by 201%. Pause duration and burst speed decreased by 391% and 250% immediately and 124% and 109% 24 h after exposure. No effects were found for burst duration or tortuosity. Our results suggest potential cascading effects on fitness and trophic interactions.

Characterization of the differential expressed genes and transcriptomic pathway analysis in the liver of sub-adult red drum (Sciaenops ocellatus) exposed to Deepwater Horizon chemically dispersed oil

The Deepwater Horizon blowout resulted in the second-largest quantity of chemical dispersants used as a countermeasure for an open water oil spill in the Gulf of Mexico. Of which, the efficacy of dispersant as a mitigation strategy and its toxic effects on aquatic fauna remains controversial. To enhance our understanding of potential sub-lethal effects of exposure to chemically dispersed-oil, sub-adult red drum (Sciaenops ocellatus) were continuously exposed to a Corexit 9500: DWH crude oil chemically enhanced water accommodated fraction (CEWAF) for 3-days and transcriptomic responses were assessed in the liver. Differential expressed gene (DEG) analysis demonstrated that 63 genes were significantly impacted in the CEWAF exposed fish. Of these, 37 were upregulated and 26 downregulated. The upregulated genes were primarily involved in metabolism and oxidative stress, whereas several immune genes were downregulated. Quantitative real-time RT-PCR further confirmed upregulation of cytochrome P450 and glutathione S-transferase, along with downregulation of fucolectin 2 and chemokine C-C motif ligand 20. Ingenuity Pathway Analysis (IPA) predicted 120 pathways significantly altered in the CEWAF exposed red drum. The aryl hydrocarbon receptor pathway was significantly activated, while pathways associated with immune and cellular homeostasis were primarily suppressed. The results of this study indicate that CEWAF exposure significantly affects gene expression and alters signaling of biological pathways important in detoxification, immunity, and normal cellular physiology, which can have potential consequences on organismal fitness.

Impacts of deepwater horizon oil on fish

An explosion on the Deepwater Horizon (DWH) oil rig in 2010 lead to the largest marine oil spill to occur in US history, resulting in significant impacts to the ecosystems and organisms in the Northern Gulf of Mexico (GoM). The present review sought to summarize and discuss findings from the 50+ peer-reviewed publications reporting effects of DWH oil exposure on teleost fish, and concludes that oil toxicity is a multi-target, multi-organ syndrome with substantial species-specific sensitivity differences. Of the 15 species tested with characterized exposures, 20% show effects at concentrations <1 μg l^-1 while 50% display effects at <8.6 μg l^-1 ΣPAH₅₀, concentrations well within the range of reported environmental levels during the spill. Cardiotoxic effects are among the most frequently reported endpoints in DWH oil exposure studies and are thought to have significant downstream effects on fitness and survival. However, additional and possibly cardio-toxic independent impacts on sensory function and behavior are reported at very low exposure concentrations (< 1 μg l^-1 ∑PAH₅₀) and are clearly deserving of further study. Available information about modes of action leading to different categories of effects are summarized in the present review. An overview of the literature illustrates that early life stages (ELS) are approximately 1-order of magnitude more sensitive than corresponding later life stages, but also illustrates that adults can be impacted at concentrations as low as 4 μg l^-1 ΣPAH₅₀. The majority of studies exploring DWH oil toxicity in fish are performed using acute exposures (1-2 days), mid-range test temperatures (26-28 °C) and measure effects at the molecular to organismal levels, leaving a pressing need for more long-term exposures, exposures at the upper and lower levels of GoM relevant temperatures, and studies investigating population level impacts.

Toxicity of weathered Deepwater Horizon oil to bay anchovy (Anchoa mitchilli) embryos

The BP-contracted Deepwater Horizon Macondo well blowout occurred on 20 April 2010 and lasted nearly three months. The well released millions of barrels of crude oil into the northern Gulf of Mexico, causing extensive impacts on pelagic, benthic, and estuarine fish species. The bay anchovy (Anchoa mitchilli) is an important zooplanktivore in the Gulf, serving as an ecological link between lower trophic levels and pelagic predatory fish species. Bay anchovy spawn from May through November in shallow inshore and estuarine waters throughout the Gulf. Because their buoyant embryos are a dominant part of the inshore ichthyoplankton throughout the summer, it is likely bay anchovy embryos encountered oil in coastal estuaries during the summer and fall of 2010. Bay anchovy embryos were exposed to a range of concentrations of two field-collected Deepwater Horizon oils as high-energy and low-energy water accommodated fractions (HEWAFs and LEWAFs, respectively) for 48h. The median lethal concentrations (LC₅₀) were lower in exposures with the more weathered oil (HEWAF, 1.48µg/L TPAH50; LEWAF, 1.58µg/L TPAH50) compared to the less weathered oil (HEWAF, 3.87µg/L TPAH50; LEWAF, 4.28µg/L TPAH50). To measure delayed mortality and life stage sensitivity between embryos and larvae, an additional 24h acute HEWAF exposure using the more weathered oil was run followed by a 24h grow-out period. Here the LC₅₀ was 9.71µg/L TPAH50 after the grow-out phase, suggesting a toxic effect of oil at the embryonic or hatching stage. We also found that exposures prepared with the more weathered Slick B oil produced lower LC₅₀ values compared to the exposures prepared with Slick A oil. Our results demonstrate that even relatively acute environmental exposure times can have a detrimental effect on bay anchovy embryos.