Abstract
Herein we investigated the cellular responses of the endemic fish species Alburnus vistonicus Freyhof & Kottelat, 2007, under the variation of several physico-chemical parameters including temperature (°C), salinity (psu), dissolved oxygen (mg/L), pH and conductivity (μS/cm), which were measured in situ. Monthly fish samplings (October 2014–September 2015) were conducted in Vistonis Lake in northern Greece, a peculiar ecosystem with brackish waters in its southern part and high salinity fluctuations in its northern part. Fish gills and liver responses to the changes of the physico-chemical parameters were tested biochemically and histologically. Heat shock protein levels appeared to be correlated with salinity fluctuations, indicating the adaptation of A. vistonicus to the particular environment. The latter is also enhanced by increased Na+-K+ ATPase levels, in response to salinity increase during summer. The highest mitogen activated protein kinases phosphorylation levels were observed along with the maximum mean salinity values. A variety of histological lesions were also detected in the majority of the gill samples, without however securing salinity as the sole stress factor. A. vistonicus cellular stress responses are versatile and shifting according to the examined tissue, biomarker and season, in order for this species to adapt to its shifting habitat.
Highlights
The ecological stability of inland and transitional waters is more vulnerable to exogenous pressures compared to marine ecosystems, as the physicochemical characteristics of freshwater environments can be highly variable by season and by water body [1]
HSP70 lowest expression levels were observed in June and the highest in December, HSP60 minimum expression levels in the gills were found in July and their maximum in August, when they were significantly higher compared to the rest months (Figure 4C)
In the case of Vistonis Lake, the results presented exhibited a similar pattern regarding HSP70 expression levels and Na+-K+ ATPase in the gills, since both exhibited their maximum levels during increasing ambient water temperature, when mean salinity values increased
Summary
The ecological stability of inland and transitional waters is more vulnerable to exogenous pressures (e.g., climate change) compared to marine ecosystems, as the physicochemical characteristics of freshwater environments can be highly variable by season and by water body [1]. These aquatic ecosystems, and especially lakes, are subject to constant anthropogenic pressures, with the impact of degradation of their ecological value [2]. The lacustrine environment is known to constantly change and affect inhabiting fish species ecology [32,33,34,35], the effect of Vistonis Lake’s continuously changing physico-chemical parameters on the biochemical and physiological responses of A. vistonicus remains unknown
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