, 1998). In Gulf killifish and sea trout, our findings were check details the same: the response to oil exposure was a decreased number of circulating lymphocytes, which makes fish more susceptible to infectious diseases. Laboratory studies of the effects of petroleum products on fish immune responses were conducted before the Deepwater Horizon disaster and findings include increased or decreased macrophage respiratory burst, depending on the chemical, the amount used and the fish species (reviewed in (Reynaud and Deschaux, 2006)). Expression analysis of immune related genes following petroleum exposure showed that they were up-regulated (Bowen et al., 2007). Genomic analysis

of Gulf killifish liver tissue demonstrated that the oil exposure caused significant biological changes (Whitehead et al., 2011). RNA-Sequence analysis of Gulf killifish from another oil-exposed site indicated that the circulating (peripheral) leukocytes were undergoing immune stress (Garcia et al., 2012). Historically,

sampling surveys demonstrated that fish from polluted waters had a higher incidence of lesions. More specifically, hydrocarbon exposure results in decreased mucus production and increased epidermal lesions and parasitism as well as impaired function of many immune responses (reviewed in Austin, 1999). Alligator gar are large, euryhaline fish that can be found throughout Gulf coastal and in-land waters. They were selected as a target species because they are bi-modal breathers Ribociclib chemical structure and could be exposed to emulsified anti-PD-1 antibody or surface contaminants. Gar are also a top-predator and may demonstrate accumulated effects of oil in the ecosystem. However, they may not demonstrate the effects seen in the other estuarine fish because they cover expansive areas and move in and out of contaminated waters. This is probably why peripheral blood smears from alligator gar in Terrebonne Bay appeared normal. Conversely, Gulf killifish live in marshes, and usually stay in a localized area (McClane, 1978). They occupy a niche that is very vulnerable to contamination, and would remain there during the

spill. It is likely this is why peripheral blood leukocyte changes were observed in these fish. After the Gulf oil spill, surface water analyses conducted by the US Environmental Protection Agency (EPA) and the Mississippi Department of Environmental Quality (MDEQ) determined that daily air and water quality was within normal ranges at monitoring sites along the MS Gulf Coast (Beasley et al., 2012). During the spill, the majority of oil was emulsified and entered the deep waters of the Gulf (Camilli et al., 2010). A large sub-surface plume was followed for months. This plume contained an amount of petroleum hydrocarbon that was double the amount of naturally occurring seepage (Camilli et al., 2010). Damaged and killed coral beds in the path of the predicted deep-water oil plume demonstrated these systems were specifically impacted by Macondo oil (White et al.