Effects of acute ammonia exposure on histopathology of liver, gill and brain in juvenile cuttlefish (Sepia pharaonis)

The aim of this study is to investigate the toxic effects of ammonia-N stress on the histopathological changes of liver, gill and brain in juvenile cuttlefish (Sepia pharaonis). The S. pharaonis,whose initial average weight was (13.80±0.65) g, were first exposed to ammonia-N for 96 hours and then the 96 hours median lethal concentration was obtained. In this study, we established a control group (0 mg/L) and four different ammonia nitrogen concentrations of 1, 3, 6, and 12 mg/L for the acute ammonia toxicity experiment according to preliminary experimental results, and each ammonia-N level was respectively sampled at 96 h. The liver, gill and brain tissues were observed by optical microscope and transmission electron microscope. The results showed that the severity of lesions clearly differed among organs with the liver showing the most extensive damages, followed in order by the gill and brain. And there was no damage to the brain tissue. The damages of liver and gill increased with increasing exposure concentration and time. It is found that the liver is bright red, swollen, and easily eroding from the 96 h after exposure to no less than 6 mg/L ammonia. Microscopical observation showed that the liver displayed hypertrophy of hepatocytes, nuclear hypertrophy, cellular peripheral nucleus, hepato cellular vacuolation, hydropic degeneration, necrosis, dilatation in sinusoids, cellular outline indistinguishable and cytolysis. The transmission electron microscope observation showed the hepatocyte nuclear crinkle deformation, the nucleolus disappearance, the mitochondrial crista disorder, the vacuolation and the outer chamber swelling, and the number of Golgi bodies decreased. Microscopical observation showed shedding epithelial cells from gill lamella, irregular array and some necrosis phenomenon, vessel of gill filaments was pycnosis or even became cavum, and branchial swelling and congestion. The transmission electron microscope observation showed gill epithelium and chloride nuclear membrane breakage, and nuclear cleavage, mitochondrion has crinkle deformation, vacuolization and incomplete breakage. While the brain tissue and the optic lobes were observed, there was no cell damage in the brain tissue.