Comparative sensitivity of six scleractinian corals to temperature and solar radiation.

Scleractinian corals were exposed to 6 combinations of temperature and solar radiation to evaluate effects on coral bleaching, survival, and tissue surface area changes during and after exposure. A recirculating coral exposure system was coupled to a solar simulator to allow laboratory testing of 6 species of Caribbean corals (Diploria clivosa, Montastraea faveolata, Porites divaricata, Stephanocoenia intersepta, Siderastrea radians, and Siderastrea siderea). Significant bleaching occurred in all of the corals exposed to high irradiance except S. siderea. Elevated light levels resulted in a decrease in photochemical efficiency for all species during the exposure period, with S. siderea showing the smallest decrease. The most prominent reductions in photochemical efficiency occurred in M. faveolata and S. intersepta, and these species exhibited extensive tissue loss and the highest mortality. In contrast to high irradiance, high temperatures significantly decreased photochemical efficiency for only D. clivosa and did not lead to severe tissue loss for this species. These results demonstrate species-specific responses to solar radiation and temperatures, with M. faveolata and S. intersepta being the most susceptible to bleaching due to high irradiance.

Histopathological Evidence of Regeneration following Hepatotoxic Effects of the Cyanotoxin Microcystin-LR in the Hardhead Catfish and Gulf Killifish.

The cyanobacterial toxin microcystin-LR (MC-LR) causes liver damage in several freshwater fish species. In the present study, two estuarine species, hardhead catfish Arius felis and gulf killifish Fundulus grandis, were injected intraperitoneally with MC-LR at 45-300 µg/kg and their livers examined histopathologically for up to 23 d postinjection (PI) in the catfish and 5 d PI in the killifish. The livers from both species exhibited extensive, diffuse hepatocellular necrosis by 6 h PI. The necrosis persisted, and by day 2 large numbers of basophilic cells had emerged throughout the liver parenchyma. These cells occurred individually or in small clusters. By 72 h, the basophilic cells appeared to be highly proliferative with numerous mitotic figures and were arranged in cords and tubules similar to mature hepatic parenchyma. Regeneration of the liver parenchyma was noted in gulf killifish at 5 d PI, as tracts of basophilic cells were still evident. In hardhead catfish, there were no signs of necrosis or proliferating basophilic cells by 9 d PI, and the hepatic parenchyma appeared normal except for the vacuolation of many hepatocytes and some areas of hepatic megalocytosis. The degenerative changes in the two species studied were similar to but more pronounced than those observed in freshwater fish species exposed to MC-LR. Evidence of regeneration from the hepatotoxic effects of MC-LR suggests that the toxin can be used to study regenerative processes in fish livers.

Diagnostic criteria for proliferative thyroid lesions in bony fishes.

Thyroid proliferative lesions are rather common in bony fishes but disagreement exists in the fish pathology community concerning diagnostic criteria for hyperplastic versus neoplastic lesions. To simplify the diagnosis of proliferative thyroid lesions and to reduce confusion regarding lesion interpretation, we propose specific criteria for distinguishing hyperplastic from neoplastic lesions. Development of these criteria was based on the examination of a large series of proliferative lesions from Japanese medaka (Oryzias latipes), lesions from other small fish species, and a reexamination of the 97 cases of proliferative thyroid lesions from bony fishes deposited in the Registry of Tumors in Lower Animals. Specific diagnostic criteria are provided for all lesion categories including follicular cell hyperplasia (simple, nodular, or ectopic), adenoma (papillary or solid), and carcinoma (well- or poorly differentiated). These criteria should assist fish pathologists in describing and categorizing naturally occurring proliferative lesions from wild fishes, lesions that develop in laboratory fishes due to suboptimal culture practices or water quality, those in fishes used in toxicological assays, and captive aquarium fishes.

Ovacystis-like condition in the eastern oyster Crassostrea virginica from the northeastern Gulf of Mexico.

Histological examination of the eastern oyster Crassostrea virginica from a study in Pensacola Bay, Florida, revealed 2 cases of abnormally large, basophilic ova that resembled cells characteristic of ovacystis disease previously reported in oysters from Maine and Long Island. The hypertrophied gametes measured up to 250 pm in diameter, had scant cytoplasm and contained granular nuclear-masses of Feulgen-positive material. Electron microscopy of reclaimed tissue revealed these masses to consist of virus-like particles (average 46 nm) similar to those reported in cases of ovacystis.

Histopathological Evidence of Regeneration following Hepatotoxic Effects of the Cyanotoxin Microcystin-LR in the Hardhead Catfish and Gulf Killifish.

The cyanobacterial toxin microcystin-LR (MC-LR) causes liver damage in several freshwater fish species. In the present study, two estuarine species, hardhead catfish Arius felis and gulf killifish Fundulus grandis, were injected intraperitoneally with MC-LR at 45-300 µg/kg and their livers examined histopathologically for up to 23 d postinjection (PI) in the catfish and 5 d PI in the killifish. The livers from both species exhibited extensive, diffuse hepatocellular necrosis by 6 h PI. The necrosis persisted, and by day 2 large numbers of basophilic cells had emerged throughout the liver parenchyma. These cells occurred individually or in small clusters. By 72 h, the basophilic cells appeared to be highly proliferative with numerous mitotic figures and were arranged in cords and tubules similar to mature hepatic parenchyma. Regeneration of the liver parenchyma was noted in gulf killifish at 5 d PI, as tracts of basophilic cells were still evident. In hardhead catfish, there were no signs of necrosis or proliferating basophilic cells by 9 d PI, and the hepatic parenchyma appeared normal except for the vacuolation of many hepatocytes and some areas of hepatic megalocytosis. The degenerative changes in the two species studied were similar to but more pronounced than those observed in freshwater fish species exposed to MC-LR. Evidence of regeneration from the hepatotoxic effects of MC-LR suggests that the toxin can be used to study regenerative processes in fish livers.