Effect of Diesel Fuel Oil Exposure on Morphology, Behavior, and Internal Organ of Freshwater Fish, Nile Tilapia ( <i>Oreochromis niloticus</i> L. 1758)

Water pollution resulting from petroleum derivatives, notably diesel fuel oil, has emerged as a significant environmental concern recently. The experiment was conducted to find out the impact of diesel oil on morphology, behavior, and changes in internal organs i.e., heart, intestine, kidney, and liver in Nile tilapia ( Oreochromis niloticus ). There were controls and three groups of Nile tilapia ( Oreochromis niloticus ) exposed to 0 mL/L (control), 0.5 mL/L, 1.0 mL/L, and 1.5 mL/L of diesel for 15 days. Several morphological changes such as a broken fin, rough scale, increased mucous, and discolored gill were recorded. The treated fish displayed erratic swimming patterns, rapid operculum movements, and hovering in the water column, displaying signs of weakness whereas the untreated (control) remained calm and normal. Probit analysis revealed that the mortality rates were increased significantly ( p &lt; 0.05) with the increase of diesel concentrations. Multiple histopathological abnormalities were found and they were fragmentation of myocardial muscle fiber and formation of degenerative vacuoles in the heart; degeneration of epithelium, submucosa, and hemorrhage in the mucosa of the intestine; hemorrhages of glomerulus and dilation of tissues in the kidney; and enlargement of central vein, degeneration of hepatocyte, dilation of the sinusoid, hemorrhage, vacuolization of hepatocytes, necrosis, and thickening of the hepatocytic cells in the liver. This study also concluded that the dissolved oxygen levels decreased with the increase of oil concentrations, which led to poor water quality and had a significant effect on morphology, behavior, histology, and mortality. This study will grow social awareness and people will handle commercial diesel oil properly during transportation. Thus, the present findings might be helpful to save aquatic animals as well as aquatic environments.