3.2. Histological examination
Signs of epitheliocystis could be clearly observed under light microscope
at a low magnification (objective 10×). Infected cells became
hypertrophied and round to oval in shape.Majority of the fish sampled
in autumn had more severe epitheliocystis with the cysts of various
sizes being evenly distributed on the gill sections. These enlarged cells
were occasionally located in the subepidermal fibrous tissue (Figs. 1
and 2). Most cysts were present in the lamellae (Figs. 2 and 3). The
cysts were evenly distributed in gill filaments of striped trumpeter;
there were approximately 60% of cysts positioned at tip of or along lamellae,
and 40% were located on filamentous epithelium of gills in
terms of locations. In some severely infected fish, cyst elicited host responses
such as infiltrationwith mononuclear cells and lamellar fusions
(Fig. 3). Lamellae containingmultiple cystswere clearly evident (Fig. 4).
The identity of infected cells was difficult to determine in the H&E
stained sections, but based on their position in the gill mostwere pavement
cells and some chloride cells. Average diameter of the cyst wassimilar for both cohorts and both sampling times (Table 2). Largest
cysts were observed in cohort B in spring and cohort A in autumn
(Table 2). There was no significant effect of sampling time on the size
of the cyst (t=0.823, df 30.256, p>0.05).