A qualitative and quantitative study of the hepatic pigmented macrophage aggregates during the breeding cycle of Ohrid trout, Salmo letnica Kar. (Teloestei, Salmonidae)

It is well known that factors such as aging and water quality may influence pigmented macrophages (PMacs) in fishes, but it is not established yet if PMacs undergo seasonal and breeding dependent variations. This study explored this caveat and reports qualitative histological and stereological data on liver PMacs from wild female Ohrid trout, Salmo letnica, during the annual breeding cycle. Data showed that a minority of PMacs contained melanin and that the vast majority of them contained only hemosiderin or hemosiderin and lipofuscin/ceroid pigment. It was suggested that this is the normal scenario for the species. One remarkable result was the demonstration of a striking increase, after spawning, of the relative and total volumes of the hepatic macrophages, both parenchyma and stroma located. Because the melano PMacs did not vary, those changes were due to fluctuations in the hemosiderin-laden PMacs. We concluded that Ohrid trout presented a pigment composition in liver macrophages that differed from other fish, including salmonids, where most liver phagocytes essentially display melanin. Our quantitative data support interspecies differences in the amount of liver macrophages and also that after spawning expansion of the macrophage pool is crucial and most likely connected with the needs of liver remodeling (leading to a decrease in hepatic mass). So, we suggested that the hormonal (sex steroidal) constellation influenced the liver macrophage pool. Additionally, we proved that the use of fish liver macrophages for biomonitoring should take into account the considerable natural breeding/seasonal dependent variations that are expected to occur.