## 3 Results
### HSPs  
HSPs expression levels in the gills and liver of _A. vistonicus_ are shown in Figure 4. In the gills, HSP70 levels exhibited their lowest in July and their highest in August, when they were also significantly higher compared to all the rest samplings (Figure 4A). In the liver, HSP70 lowest expression levels were observed in June and the highest in December, when they were also significantly higher compared to the rest of the samplings, with the exception of those in February (Figure 4A).  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Histological Lesion** & **OCT** & **NOV** & **DEC** & **FEB** & **MAR** & **APR** & **JUN** & **JUL** & **AUG** & **SEP** \\ \hline
**Epithelium detachment (edema) at the secondary lamella** & +(3) & - & +(4) & +(2) & +(3) & +(3) & +(2) & - & +(2) & +(4) \\ \hline
**Hyperplasia of the primary lamella** & +(3) & - & +(3) & +(2) & +(4) & +(2) & +(2) & +(1) & +(1) & +(3) \\ \hline
**Hyperemia (aneurys) of the secondary lamella** & +(2) & - & - & - & - & +(2) & +(1) & +(1) & - & - \\ \hline
**Hyperplasia of the edge of the secondary lamella** & - & - & - & - & - & - & - & - & - & - \\ \hline
**Hypoplasia (small size) of the secondary lamella** & - & - & - & - & - & - & - & +(1) & - & - \\ \hline
**Hyperplasia of the secondary lamella** & - & - & - & +(2) & +(3) & - & - & +(1) & - & - \\ \hline \hline \end{tabular} The number of fish in which lesions are observed is mentioned in parentheses.  
\end{table}
Table 1: Presence (+) and absence (\(-\)) of histological lesions detected in gill samples of the freshwater fish species _Alburnus vistonicus_ in Vistonis Lake (Northern Greece), during the period October 2014–September 2015 (no samples were obtained in January 2015 due to unfavorable weather conditions).  
Figure 3: Histological lesions detected in the gills of the freshwater fish species _Alburnus vistonicus_ in Vistonis Lake (Northern Greece), during the period October 2014–September 2015. (**A**) November sampling. Normal gills architecture. (**B**) April sampling. Hyperplasia of the primary lamella (arrow) and epithelium detachment (edema) of the secondary lamella (arrowhead). (**C**) April sampling. Hyperplasia of the primary lamella (arrowhead). Arrow shows a secondary lamella. (**D**) June sampling. Aneurys of the secondary lamella (arrows).  
HSP90 levels in the gills exhibited seasonality, with their minimum in October and maximum in February. The expression levels in February were significantly higher compared to those in the rest of the months (Figure 4B). In the liver, HSP90 minimum expression levels were observed in August, while the maximum in December. HSP90 levels exhibited seasonality, with higher values during the winter and autumn months and lower during the summer ones (Figure 4B).  
HSP60 minimum expression levels in the gills were found in July and their maximum in August, when they were also significantly higher compared to the rest months (Figure 4C). In the liver, HSP60 levels exhibited their lowest in July. Protein expression levels were significantly lower in April, June, July and November compared to those in October, December, February, August and September. Moreover, HSP60 levels in September were significantly higher compared to those from the rest months, with the exception of August (Figure 4C).