Alligator gar Atractosteus spatula acclimated to brackish water (9 ppt) were exposed to water accommodated fraction oil loadings (surrogate to Macondo Deepwater Horizon, northern Gulf of Mexico) of 0.5 and 4.0 gm oil/L tank water for 48 h. The surrogate oil was approximately 98% alkanes and alkynes and 2% petroleum aromatic hydrocarbons. The 2% petroleum aromatic hydrocarbons were predominately naphthalene. After 48 h, naphthalene levels in fish liver exposed to 0.5 or 4 gm oil/L were 547.79 and 910.68 ppb, while muscle levels were 214.11 and 253.84 ppb. There was a significant decrease in peripheral blood lymphocyte numbers and a significant reduction of granulocytes in the kidney marrow of the same fish. Tissue changes included hepatocellular vacuolization and necrosis, necrotizing pancreatitis, renal eosinophilia, and splenic congestion. After 7 days recovery, liver naphthalene levels decreased to 43.59 and 43.20 ppb, while muscle levels decreased to 9.74, and 16.78 ppb for oil exposures of 0, 0.5 or 4 g/L. In peripheral blood and kidney marrow, blood cell counts returned to normal. The severity of liver and kidney lesions lessened after 7 days recovery in non-oiled water, but splenic congestion remained in all gar.

Diazinon is a widely used household and agricultural pesticide that accumulates in the aquatic environment and adversely affects non-target organisms such as mammals, birds, and fish. Sub-lethal pesticide levels occur in natural waters, and can impact the health, physiology and fitness of fish populations. This study was conducted to assess the effects of chronic, sub-lethal diazinon exposure to skin, liver, kidney, spleen, heart, gut, intestine, and gas bladder tissues of alligator gar, Atractosteus spatula. In two studies, gar were exposed to sub-lethal concentrations of 0.01, and 0.1 mg/L diazinon for 15 and 30 day periods. Skin, gills, liver, and kidney of exposed fish demonstrated remarkable microscopic lesions. These changes included skin lesions in the head and body, which started as white spots and progressed into deep ulcerations, hepatic vacuolation, swollen hepatocytes, steatosis, aggregation of macrophages, necrosis, and hepatic fibrosis. Gill tissues demonstrated epithelial hyperplasia in the secondary lamellae. Vacuolar degeneration was also present in the hematopoietic tissues of the kidney. Lesion occurrence and severity were correlated to increased diazinon dose and exposure time. Our findings revealed the harmful effects of chronic, sub-lethal diazinon exposure on alligator gar, and suggest other aquatic organisms may also be affected by sub-lethal concentrations of pollutants in their environment.

Anthropogenic factors seriously affect water quality and adversely affect fish populations. Agricultural runoff accumulates in the Mississippi River and the coastal estuaries. Alligator gar (Atractosteus spatula) inhabits these waters and is impacted by agricultural pollution, petrochemical contaminants and oil spills. These fish are bimodal air breathers, and use a primitive lung as an accessory organ. The gas bladder, or Air Breathing Organ (ABO) of alligator gar (Atractosteus spatula), is a vascularized air sac located dorsal to the body lumen. It has characteristics of amphibian lungs. Alligator gar air-breathing organs function to supplement branchial respiratory exchange with aerial gas exchange. The alligator gar gas bladder is an elongated air sac that originates dorsal to the pharynx. Air enters through a pharyngeal-esophageal duct that is controlled by two glottal ridges. The pharyngeo-esophageal duct is approximately 5mm long and is lined by ciliated columnar epithelium that is continuous with the central canal epithelium. The gas bladder has a central canal that subdivides the bladder into right and left lobes. Each lobe is further divided by septa into series of air spaces. The septa consist of blood vessels and smooth and striated muscles. Air circulates throughout the central canal, lobes and air spaces. The thickness of the septa is determined by underlying, supportive striated muscle. The internal surface of the gas bladder is a continuous respiratory epithelial layer that includes mucus cells, pneumocytes, and ciliated epithelial cells. An understanding of the normal tissue characteristics of this air breathing organ provides a baseline for studying the effects of environmental toxins on this organ.