Fish Exposure Studies Begin at Mote Marine Laboratory

Understanding the immediate impact of oil spills on fish is one of the goals of GoMRI researchers in the coming months during new C-IMAGE fish exposure program.

Through a series of experiments, using sub-lethal exposure levels of oil and three species of unexposed adult marine fishes, answers to questions about biochemical and physiological changes in the days and weeks following an oil blowout will aid researchers in understanding potential short and long-term impacts on the Gulf of Mexico ecosystem.

The Center for Integrated Modeling and Analysis of Gulf Ecosystems (C-IMAGE) and partners at Mote Marine Laboratory began a ground-breaking study to evaluate sub-lethal responses in targeted marine fish species to oil contamination.

During oil spills, like Deepwater Horizon, skin lesions (open sores) on fish may be attributed to prolonged contact with oil. Fishermen from the northern Gulf of Mexico first reported these lesions in their catches beginning in winter 2010 and researchers followed with studies in 2011. However, the status of these fisheries prior to the oil spill was a mystery due to a lack of baseline data in the region.

Dr.’s Dana Wetzel and Kevan Main from Mote Marine Laboratory are leading their team of researchers at the Mote Aquaculture Park in Sarasota, FL. Wetzel and Main will study effects of oil on hatchery reared species of adult pompano, red drum, and flounder, which occupy different habitats, in the open ocean, nearshore, or bottom, respectively.

“Most oil exposure studies target early life stages of animals because they are considered to most vulnerable,” said Dr. Wetzel, C-IMAGE’s ecotoxicology task lead. “However, we believe that determining sublethal responses in adults that suggest a decline in immune status, ability to reproduce, and gene integrity are critical for ecosystem conservation.”

These designed studies will test three different species of marine fish to oil through four pathways: ingestion, sediment contact, water contact, and direct injection. The experiments will measure changes in immune function, reproduction and DNA damage along with many other biological parameters.

Direct Injection:

On July 7th, Mote Marine Laboratory began their first exposure study to understand the extreme effects of oil exposure to a fish. Through an intra-peritoneal injection (body cavity injection; IP), all three species of fish were acutely exposed to a mixture of Louisiana crude oil and corn oil (corn oil acting as a carrier).

Following 24, 48, and 72 hour exposure periods, fish were sampled for blood, muscle and organ tissue, otoliths (ear bones), and bile. Careful analysis of these samples will be critical for understanding the extreme cases of oil exposure and what might be observed during the other exposure trials.

Wetzel acknowledges that, “Direct injection of oil is not a realistic oil exposure pathway.  However, by carrying out this IP study, we will be able gain insight to confirm which biological health markers may be compromised or damaged during the remaining exposure scenarios.”

Dietary Exposure:

One pathway by which fish could be exposed to oil is through their diet. Oil in seawater can be adsorbed onto potential food particles (plankton, detritus, etc.) making its way into the food web and into fish. One question the Mote exposure studies will address is the efficiency of the metabolization of ingested oil – how well the fish breaks down oil compounds – in addition to other health impact assessments.  Researchers will use oil-coated food pellets to investigate how fish, in these trials red drum, respond to hydrocarbons by ingesting sub-lethal levels of oil.

Ingestion experiments are set to begin in Fall 2015.

Oil-Water Exposure:

A fishes lifestyle determines the pathway of oil exposure; bottom-dwelling fish have contact with sediments, while open-water fish, or pelagic fish, are exposed by the water soluble components from spilled oil. The effect of an oil-water mixture (water accommodated fraction or WAF) on pelagic fish like pompano will be studied as part of the new exposure studies.

Adult pompano in this study will be exposed to a moderate concentration of WAF, which will decline to zero oil concentration levels as new sea water is cycled through, known as a spiked-declining exposure method. These results will show the potential impacts of spilled oil exposure to open-water, pelagic fish species.

Following the oil-water exposure studies, pompano will be moved into spawning tanks to reproduce.  Reproductive fitness will be measured by the researchers through sperm and egg counts, hatch success, development abnormalities and egg/embryo biochemical composition.  This information will be valuable in predicting possible impacts of spilled oil on the next generation of oil-exposed fish.  

Trials for the WAF studies are set to begin in early 2016

Sediment Exposure:

Flounder are bottom-dwelling (benthic) fish spending their adult lives in contact with the ocean floor and sediments. During oil blowouts, sediments trap and retain oil in layers on the sea floor. Benthic dwelling fish are at risk of chronic oil exposure through these sediments.

This exposure study will expose flounder to oil-tainted sediments for several weeks to observe low level chronic conditions of exposure through contact with contaminated sediments. Sediment exposure studies are planned for Fall 2016.

“Exposure trials with sub-adult and adult fishes are challenging to carry out because of the large water volume required to implement these studies,” said Dr. Kevan Main, a Mote Marine Laboratory research focusing on fish reproduction. “Exposure trials will be conducted at Mote Aquaculture Park in tanks that are connected to a water treatment system; this system will filter and remove waste and oil from the allowing the reuse of clean water for exposure trials.”

The main goal of C-IMAGE is to advance understanding of the processes, mechanisms, and environmental consequences of marine oil spills. The results of these planned exposure studies have broad contributions to C-IMAGE II research by providing survival and reproduction information to the team’s ecosystem modelers for help in estimating population level responses to oil spills.

This research was made possible by a grant from BP/The Gulf of Mexico Research Initiative. Founded in 1955, Mote Marine Laboratory & Aquarium is celebrating its 60th year as an independent, nonprofit 501(c)3 research organization. Mote’s beginnings date back six decades to the passion of a single researcher, Dr. Eugenie Clark, her partnership with the community and philanthropic support, first of the Vanderbilt family and later of the William R. Mote family.