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.

Digestive tubules from intertidal and subtidal oysters, Crassostrea virginica, were histologically examined to gain a better understanding of their normal morphology during high and low tides and while being held out of water for up to 72 h. Intertidal and subtidal oysters from Bayou Texar, Pensacola, Florida, were collected from adjacent sites and processed for histological examination. A digestive tubule ratio for each oyster was determined by measuring the inside to outside tubule thickness from 20 tubules per animal. Digestive tubules with high tubule ratios (approaching 1.0) had low cuboidal epithelia, whereas tubules with low ratios (approaching 0.0) had columnar epithelia. In tidal studies, intertidal oysters sampled 13-15 h after emersion at low tides had no crystalline styles and high tubule ratios, whereas subtidal oysters collected at the same time exhibited crystalline styles and low tubule ratios. Intertidal oysters sampled 6-14 h after submersion at high tides had crystalline styles present and low tubule ratios, whereas subtidal oysters also possessed crystalline styles and low tubule ratios. These data indicate that intertidal C. virginica respond to tidal cycles with changes in tubule morphology, whereas subtidal oysters do not. In holding experiments, digestive tubule ratios in intertidal and most subtidal oysters held out of water did not significantly change over time, which may be a consequence of collection stress (quiescence and/or anaerobic metabolism).

Oysters sampled in February, 1992 from a low salinity site (3 ppt) in Apalachicola Bay, FL showed digestive tubule atrophy when compared with oysters from a higher salinity site (18 ppt) 16 km away. Experiments designed to induce tubule atrophy in the laboratory consisted of two starvation and two salinity stress tests. To quantify tubule condition for each oyster, inside to outside tubule diameter ratios were calculated from 20 tubules per animal using an ocular micrometer. Higher tubule ratios indicated greater tubule atrophy. The experiments showed that poor nutrition, during low salinity, may have played a significant role in the tubule atrophy of Apalachicola Bay oysters.

An ovarian mycosis in a topsmelt Atherinops affinis (Ayres), collected from Elkhorn Slough, Monterey County, California, USA, is reported. The fungus caused a considerable host response resulting in numerous granulomas and follicular atresia. Based on morphologic characteristics, the fungus was probably a member of the class Oomycetes. This is the first report of an invasive ovarian mycosis in a marine fish.

American oysters Crassostrea virginica exposed to high concentrations (600 mg I-') of nnitrosodiethylamine (DENA) during winter (February to May) showed significant enhancement of an epizootic apicomplexan parasite, Perkinsus rnarinus.The parasite reproduced and caused atypical lesions in exposed oysters in water temperatures at its lower range (20°C).The reasons for this enhancement are not clear but may reflect damage to the oysters' nonspecific, cellular defense mechanisms by the DENA without concomitant negative effects on the parasite.

Abstract. Sheepshead minnows, Cyprinodon variegatus Lacépède, exposed to 5.5 to 31 μg/1 of the herbicide trifluralin, throughout their first 28 days of life, developed a heretofore undescribed vertebral dysplasia. This dysplasia consisted of semi‐symmetrical hypertrophy of vertebrae (three to 20 times normal), characterized by foci of osteoblast and fibroblasts actively laying down bone and bone precursors. Effects of the abnormal vertebral development were dorsal vertebral growth into the neural canal, ventral compression of renal ducts, and longitudinal fusion of vertebrae. Pish, exposed for 51 days to 16.6 μg/1 trifluralin and thereafter depurated for 41 days, showed no increase in vertebral dysplasia during depuration; however, residual spinal column damage was evident. Serum calcium concentrations were elevated in adult fish exposed for 4 days to 16.6 μg/1 trifluralin. Fluorosis or mimicry of hypervitaminosis A are considered possible mechanisms for the osseous effect, but are not considered to be the only possible causes. The highly predictable nature of this disorder in experimental exposures strengthens the probability that young fish may serve as experimental models for determining effects of chemicals on early vertebrate ontogeny, particularly in regard to skeletal development.

Scoliosis in fish is caused by several diverse agents that possibly act on the central nervous system, neuromuscular junctions, or ionic metabolism. The organochlorine pesticide Kepone induces scoliosis in the sheepshead minnow. Some effects associated with Kepone-induced scoliosis in these fish are disruption of myotomal patterns, inter- and intramuscular hemorrhage, fractured centra of vertebrae, and death. The histological syndrome of Kepone poisoning in fish and the clinical syndrome in humans suggest that the nervous system is a primary target for Kepone and that scoliosis is a secondary effect of Kepone poisoning in fish.