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A study of microfauna, associated with pathological changes in the gills of Atlantic salmon, Salmo salar L., was conducted over 2001-2002. Monthly samples of 1(+) salmon smolts were taken, protozoan populations were quantified and gill health was assessed histologically. Protozoan densities were correlated with pathological changes, in order to determine their possible role in lesions in the gills. The most severe gill tissue changes were observed in summer/autumn and the least in spring. A diverse polyphyletic protozoan community was observed colonizing the gills, including Neoparamoeba sp., other amoebae, scuticociliates, Ichthyobodo-like flagellates, trichodinid ciliates and prostomatean ciliates. The earlier gill tissue changes in the gill were not always associated with the presence of these microorganisms, whereas amoebae (other than Neoparamoeba sp.), Ichthyobodo-like flagellates and trichodinid ciliates correlated with augmenting gill lesions. Neoparamoeba sp. was present, but its abundance did not correlate with the disease. This study suggests that a diversity of protozoans including Ichthyobodo-like flagellates, trichodinid ciliates and amoebae other than Neoparamoeba sp. are involved in the aetiology of amoebic gill disease in the Irish situation.

A 2-year study was carried out on amoebic gill disease (AGD) involving monthly samples of 1+ Atlantic salmon, Salmo salar L., smolts, histological assessment of the gills and analysis of environmental data. Gill pathology was seen before amoebae could be detected microscopically. These changes in gill integrity were associated with marine environmental conditions, particularly elevated ammonium, nitrite and chlorophyll levels. The results suggest that the environmental changes predispose salmon to colonization by amoebae and ciliates. High densities of histophagous scuticociliates were observed in the gills during periods of advanced gill pathology. A number of different amoebae were observed in close association with gill pathology. Neoparamoeba was not seen in high densities, nor was it associated with gill pathology, indicating that Neoparamoeba may not be the primary agent of the AGD in Irish salmonid culture.

The major research themes in poikilotherm leukaemias, and their progress over the past two years are reviewed. Despite the fact that poikilotherms represent 99% of the animal world including man, background knowledge on most poikilotherm species is sparse. Furthermore, haemic systems in many poikilotherms have functions different to those of homeotherms. Most progress is being made in relation to lethal blood mutant neoplasms in Drosophila, leukaemias of farmed salmonids among the fishes, and among shellfish, the hemic sarcomas of bivalves. The hypothesis that epizootic neoplasia in fish and shellfish populations could be indicative of environmental pollution is being refined in the light of recent studies; environmental xenobiotics are no longer considered to play a primary aetiological role in either lymphomas and leukaemias of fish or haemic sarcomas of bivalves, although xenobiotics may have a primary role in other poikilotherm neoplasms.

Examination of the cells of lymphoreticular neoplasms of the northern pike (Esox lucius L.) by electron microscopy has demonstrated the presence of unusual cytoplasmic crystalloid inclusions in cells of a spontaneous trunk tumor. The ultra-structural analysis revealed that the inclusions are composed of parallel arrays of filaments associated with rows of particles. This is designated as "particle-filament complex". The filaments of the complex measured 90--120A in diameter and 0.6--2.8 micron in length. A row of dense particles measuring 250A in diameter was arranged in regular manner between the parallel filaments. It is of interest that the complex was always accompanied by an unusual structure of nucleus of the tumor cell. The nuclei were composed entirely of filaments which were distorted and closely packed. The significance of the particle-filament complex associated with altered nucleus remains to be determined.

A 2-year study was carried out on amoebic gill disease (AGD) involving monthly samples of 1+ Atlantic salmon,Salmo salarL., smolts, histological assessment of the gills and analysis of environmental data. Gill pathology was seen before amoebae could be detected microscopically. These changes in gill integrity were associated with marine environmental conditions, particularly elevated ammonium, nitrite and chlorophyll levels. The results suggest that the environmental changes predispose salmon to colonization by amoebae and ciliates. High densities of histophagous scuticociliates were observed in the gills during periods of advanced gill pathology. A number of different amoebae were observed in close association with gill pathology.Neoparamoebawas not seen in high densities, nor was it associated with gill pathology, indicating thatNeoparamoebamay not be the primary agent of the AGD in Irish salmonid culture. [ABSTRACT FROM AUTHOR]