Do macrophage centres in freshwater fishes reflect the differences in water quality?

Macrophage centres have been considered as a potentially useful indicator of fish health. In this histological work we tested this hypothesis with macrophage centres (MCs) in the spleen, the liver and the hematopoietic part of the kidney of two common freshwater fish species in Finland, perch (Perca fluviatilis) and roach (Rutilus rutilus). Samples were collected over 5 seasons from a system of 4 lakes providing a gradation in water quality. The mean number of MCs/mm(2) and the area covered (mu m(2)/mm(2)) by them differed between individual fish, species, organs, and lakes, with interactions amongst these factors. Hemosiderosis was recorded from the spleen and liver of both fish species; amounts differed between species of fish, organs, and lakes. None of the observed patterns agreed with rankings of water quality, and we conclude that macrophage centres have limited usefulness as indicators of pollution.