Effects of chronic exposure of greenlip abalone, Haliotis laevigata Donovan, to high ammonia, nitrite, and low dissolved oxygen concentrations on gill and kidney structure

After chronic, sublethal bioassays of juvenile greenlip abalone, Haliotis laevigata Donovan, to reagent ammonia, nitrite, and low dissolved oxygen, tissue samples were dissected for histological analysis. Exposure to the highest ammonia treatment (0.188 mg of free ammonia-nitrogen ([FAN]L^-1)) resulted in little difference to the gills of these abalone, relative to the controls (0.006 mg of FAN L^-1), whereas at this concentration, the right kidney showed decreased tubule definition and enlarged tubule lumen. Exposure to 7.8 mg of NO₂-N L^-1, resulted in gill lamellar thickening and epithelial lifting along with a proliferation of mucous cells. The proportion of kidney cell contents occupied by granules increased at this nitrite concentration. Associated with this change in kidney structure was an increase in basally located eosinophilic cytoplasm. Gill mucous cells from abalone exposed to depressed dissolved oxygen levels (55% oxygen saturation) exhibited more intense staining, indicative of a change in mucous composition. Some necrosis of gill epithelium was evident, either as a result of or in association with the occurrence of Ciliates (Ancistrocomidae) between the gill lamellae. Right kidney tissue did not exhibit any obvious changes in relation to exposure to low dissolved oxygen levels. Chronic exposure to slight oxygen supersaturation (117%) caused no apparent effects on gill or kidney structure.