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Infections by trematodes are among the most common fish-borne zoonoses. Metacercariae of the Family Heterophyidae in marine and freshwater fishes are nonfastidious in their choice of definitive hosts, and therefore, cause infections in human and domestic animals. In the present study, species-specific polymerase chain reaction (PCR) assays were developed for identifying and differentiating the various species examined. Sequencing and aligning the 18S (SSU) rDNA revealed interspecific variation for which species-specific DNA oligonucleotides were designed and used for the identification of 6 heterophyid species recovered from piscivorous birds. The oligonucleotides were further used to evaluate the various stages (cercariae recovered from snails, metacercariae recovered from fish and adult trematodes) of the digeneans. By applying this method we elucidated for the first time the life cycle of Pygidiopsis genata. The phylogenetic interrelationship among the newly sequenced species of Heterophyidae is outlined.

Examined fish of the genus Baryancistrus (Loricaridae) from Rio Xingu in central amazonian Brazil were found infected with extrasporogonic stages of Sphaerospora sp. (Myxosporea) in the blood and sporogonic stages in the glomeruli with the resulting escape of the sporogony products into the renal tubules, apparently when the mesangial tissue in the Bowman's capsule collapsed. Spores were seen evacuating via the urinary tubules. Blood stages were initially 2.1 x 2.8 to 2.8 x 2.8 microns in size, and when fully differentiated reached 5.6 x 5.6-5.6 x 7.0 microns; in blood smears they were 11.2 x 8.4 to 14 x 8.4 microns. Bisporoblasts in the glomerular taft were 9.8 x 7.0 microns, premature spores were 5.6 x 4.2-5.6 microns.

Epithelial hyperplasia was the most distinctive pathological change in gill filaments of striped bass, Morone saxatilis (Walbaum), from the lower Chesapeake Bay infested by Ergasilus labracis Krøyer. This tissue reaction initiated in the filament area most adjacent to the mouth of the attached parasite. Interruption of parasite egg sac production and eventual dislodgement associated with swelling of the gill filaments occurred unilaterally on gill arches of either side of the branchial basket. The largest number of parasites in all fish was found on the first outer hemibranch while abundance on successive hemibranches decreased in rank order. Copepods on the inner hemibranch, however, were least numerous on the first inner hemibranch and more numerous on the fourth inner hemibranch. On the whole, the number of parasites attached to the outer hemibranch outnumbered the number of parasites established on the inner hemibranchs. This differential settlement was most evident in low to moderate infections and became less apparent in heavy infections. Newly settled copepods showed highest abundance on the third arch and least abundance on the first and fourth arches. The causes for this differential distribution on the gill arches are discussed.

Caligus minimus (Otto, 1821) is a common parasite of Dicentrarchus labrax in Bardawil Lagoon and it also occurs sporadically on D. punctatus in this lagoon. It has also been found on D. labrax which were recently established in the Gulf of Suez. The incidence as well as the intensity of infection showed a distinct pattern of seasonal variation with maximum levels during winter and early spring and lowest levels of infection during summer and early autumn. Overall infection levels also showed distinct annual variation. Occurrence of larval stages on the fish followed the seasonal pattern observed in infections by adults copepods. The highest occurrence was observed every year in May. However, at any month of the year ovigerous females, and at least a few copeptides or chalimi may be found. Spatial distribution of infection among the fish was significantly contagious and with some exceptions followed the Poisson log normal distribution. However, the magnitude of overdispersion showed distinct seasonal fluctuations, with more extreme overdispersion in summer and autumn. These fluctuations apparently resulted from the diversity of temperature and salinity conditions in the lagoon which were most extreme during the summer and autumn. Positive correlation between host size and infection was evident only in the winter and spring months with highest levels of infection in the largest fish. Female copepods usually out number male copepods. The dominance of female over males was also evident in the preadult stages.

The article reports on the occurrence of lymphocystis virus infections in the Gulf of Aqaba, Red Sea. Sparus aurata L. has been cultured in the Gulf of Aqaba by the Mariculture Laboratory of the Israel Oceanographic and Limnological Research since 1973. The prevailing water temperatures in the Gulf water range annually from 23 to 26 degrees C and the salinity is about 40%. Maintenance offish in high densities, frequent handling, netting and transfer, which always results in minor injuries and abrasions to fish skin, could undoubtedly promote transmission of the virus and at the same time stress the fish, hence reducing their tolerance to infection.

Ulteastructural study of epitlieliocystis organisms from gills of Sparus aurata (L.) and Liza ramada (Risso) revealed in each fish a new form of the organism which differed from epitheliocystis organisms previously described. In their size range, the presence of a plasma membrane, a trilaminated cell wall and a central nucleoid, these organisms resembled chlamydial organisms (PLT). However they differed from them in the following respects: in both species several morphological forms were recognized; hyphae or mycelium-like forms and individual units, not comparable to any of the successive units described for Chlamydia organisms. Both organisms were contained within an inclusion in the host cell, but in epitheliocysts from S. aurata apparently intracytoplasmic forms were also observed. Ultra-structural studies of the cytoplasmic wall of the epitheliocystis inclusion in S. aurata suggest that the epitheliocystis cyst remains contained in a single unruptured hypertrophied cell, while in L. ramada the final cyst is formed through the coalescence of several epithelial cells. [ABSTRACT FROM AUTHOR]