A quantitative study of the hepatic eosinophilic granule cells and rodlet cells during the breeding cycle of Ohrid trout, Salmo letnica Kar. (Teloestei, Salmonidae).

Fundamental questions remain on the nature and role of fish eosinophilic granule cells (EGCs) and rodlet cells (RCs). A poorly studied aspect is their suspected seasonality of occurrence under normal circumstances. In the liver of female Ohrid trout, Salmo letnica, we detected EGCs and RCs associated with stromal components. Both cell types could be considered a normal liver component in that wild fish population. A stereological study was performed to investigate eventual seasonality / breeding-related alterations in the amount (relative and total volumes) of EGCs and RCs. Differences only existed in the quantity of RCs; increasing from the earliest stages to the more advanced stages of ovarian maturation. EGCs made a greater pool than RCs only at early- and late vitellogenesis. Based on the breeding related fluctuations we suggest there is a hormonal regulation, by sex steroids, of the RCs liver content. Moreover, our data endorses the idea that, when using changes in the RCs pool as a biomarker, the fish breeding status must be considered as a potential source of changes in the RCs pool.