Laboratory Studies Examine How Oil Spills Affect Physical and Behavioral Aspects of Gulf Fish

Dr. Christina Pasparakis analyzes different life stages of mahi-mahi embryos under a stereomicroscope. (Photo by Dan DiNicola)

Dr. Christina Pasparakis analyzes different life stages of mahi-mahi embryos under a stereomicroscope. (Photo by Dan DiNicola)

Oil from the Deepwater Horizon incident and the chemical dispersants applied during response efforts affected many ecologically and economically important fish species in the Gulf of Mexico. Scientists with the research consortium RECOVER (Relationship of Effects of Cardiac Outcomes in fish for Validation of Ecological Risk) have been studying how oil and dispersant exposure affect fish by combining molecular approaches and state-of-the-art organ level and whole animal physiology.

Here are brief recaps of seven recent RECOVER laboratory-based studies that used environmentally relevant concentrations of oil and dispersant chemicals as measured during and after Deepwater Horizon. These results improve our knowledge about toxic mechanisms induced by oil and dispersant exposure, which helps provide a foundation for predicting effects on fish and inform future spill response.

Scientists examined the behavior and olfactory acuity of adult damselfish that had been exposed to crude oil when presented with chemical alarm cues. The treated damselfish that were returned to control conditions had a reduced ability to detect and failed to avoid olfactory cues that help fish evade predation. A failure to recognize olfactory stimuli may, in part, help explain declines in Gulf of Mexico damselfish populations through 2014 and points to the importance of evaluating sublethal effects of oil exposure, which may secondarily increase mortality. The researchers published their findings in Environmental Science & Technology: Damsels in distress: Oil exposure modifies behavior and olfaction in bicolor damselfish (Stegastes partitus). Data for this study are publicly available through the Gulf of Mexico Research Initiative Information and Data Cooperative (GRIIDC) at DOIs 10.7266/n7-48jn-7a47 and 10.7266/N7KH0KQ9.

Building upon previous research that suggested cardiac impairment may not be related to the observed reduced swim performance in oil-exposed young adult red drum, scientists assessed if impaired mitochondrial function in swimming muscles could help explain the reduced swim performance. Using high resolution mitochondrial respirometry, they found that mitochondrial dysfunction likely does not underlie impaired swimming performance nor is it associated with oil exposure at concentrations relevant to Deepwater Horizon. The researchers published their findings in Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology: Oil-induced responses of cardiac and red muscle mitochondria in red drum (Sciaenops ocellatus). Data for this study are publicly available through GRIIDC at DOI 10.7266/n7-y9mb-fn45.

Scientists examined the social behavior of oil-exposed Atlantic croaker that live in groups, which serves to improve foraging and successful reproduction and to reduce predation. Oil exposure impaired the group’s cohesion as there was increased distance between oil-exposed and controlled fish, and oil-exposed fish exhibited reduced voluntary movement speed. The presence of a single oil-exposed fish disrupted the entire group’s behavior, which may have implications for reduced ecological success. The researchers published their findings in Scientific Reports: Oil exposure alters social group cohesion in fish. Data for this study are publicly available through GRIIDC at DOIs 10.7266/N77D2SNH and 10.7266/N73N21WQ.

Researchers assessed how exposure to crude oil affects the way that early life stage mahi mahi handle ammonia and urea excretion and accumulation. Exposure modestly increased urea production and impaired ammonia excretion in hatched larvae; however, the overall ammonia and urea handling became stable by the test’s end. The results suggest that the increased production of ammonia and urea reinforces previous work that increased energy demand in oil-exposed embryos is fueled by protein metabolism and urea synthesis plays a role in ammonia detoxification in oil-exposed mahi embryos. The researchers published their findings in Aquatic Toxicology: The effects of Deepwater Horizon crude oil on ammonia and urea handling in mahi-mahi (Coryphaena hippurus) early life stages. Data for this study are publicly available through GRIIDC at DOI 10.7266/n7-q77z-bm73.

Researchers evaluated the transcriptomic and phenotypic developmental impacts of Corexit 9500A dispersant and chemically-dispersed Deepwater Horizon surface oil on mahi mahi embryos. There was no observable relationship between increasing dispersant concentration and enhanced fraction of dissolved oil compounds nor with mortality, phenotypic malformations, or increased differential gene expression. Though dispersant did not alter gene expression, dispersed-oil mixtures changed ion signaling consistent with earlier studies on oil-treated mahi that suggest heart- and eye-related genes are highly sensitive endpoints of dispersed oil toxicity in mahi. The researchers published their findings in Aquatic Toxicology: Effects of Corexit 9500A and Corexit-crude oil mixtures on transcriptomic pathways and developmental toxicity in early life stage mahi-mahi (Coryphaena hippurus). Data for this study are publicly available through GRIIDC at DOI 10.7266/n7-sfa3-9041.

Using available data from existing studies, researchers assessed how oil exposure may affect fishes’ ability to tolerate typical environmental stressors, such as fluxes in temperature, dissolved oxygen, salinity and pH. They concluded that sub-lethal oil exposure can compromise the ability of fish to successfully navigate normal environmental disturbances and that more oil toxicity studies are needed that consider organismal responses to environmental stress as a quantifiable endpoint of oil toxicity, as it is an important component of any toxicant’s adverse outcome pathway. They published their findings in Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology: Oil toxicity and implications for environmental tolerance in fish.

Researchers found that whole-transcriptome sequencing of fish mucus for oil exposure testing is a promising non-invasive alternative to lethal sampling methods. They tested the efficacy of epidermal mucus mRNA as a source for noninvasive sampling and found that it compared to that of tissue analysis. The mucus mRNA revealed a differential expression of well-established PAH biomarkers and transcripts involved in immune response, cardiotoxicity, and calcium homeostasis that parallel molecular responses in whole embryos. The researchers published their findings in Environmental Science & Technology Letters: Whole-transcriptome sequencing of epidermal mucus as a novel method for oil exposure assessment in juvenile mahi-mahi (Coryphaena hippurus). Data for this study are publicly available through GRIIDC at DOI 10.7266/n7-m7d5-nk45.

These studies illustrate that anthropogenic perturbations can have complex and potentially lasting effects on our delicate ecosystems, particularly fish, and the effects can vary among species and life stages. For example, the above laboratory-based experiments documented olfaction disruption in adult damselfish, schooling behavior disruption in juvenile Atlantic croaker, and altered waste handling in early life stage mahi mahi. There may be differing or multiple oil- and dispersant-induced toxicity that affects swim performance. For example, reduced swim ability in young adult drum was not related to muscular impairment and may not be solely related to cardiac impairment, although earlier studies suggested potential impaired swim performance due to reduced cardiac function in red drum larvae and cardio-respiratory function in juvenile cobia (Study Finds Oil Exposure Reduces Cardiac Function and Survival in Red Drum Larvae and Study Finds Oil Exposure Reduces Cardiorespiratory Function in Cobia Fish). Though there were no altered gene expressions from dispersed-oil exposure observed in mahi mahi embryos, there was changed ion signaling that could affect pathways and genes important for cardiac function and vision, which is in agreement with an earlier study (Study Suggests Wider Range of Mahi-Mahi’s Genetic Responses to Oil Exposure).

Here are additional laboratory-based studies that investigated oil and dispersant effects on Gulf of Mexico fish:

By Nilde Maggie Dannreuther and Stephanie Ellis. Contact with questions or comments.


This research was made possible in part by a grant from the Gulf of Mexico Research Initiative (GoMRI) to the Relationship of Effects of Cardiac Outcomes in Fish for Validation of Ecological Risk (RECOVER) consortium and RECOVER II.

The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research. All research data, findings and publications will be made publicly available. The program was established through a $500 million financial commitment from BP. For more information, visit

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