Changes in splenic melano-macrophage centres of dab Limanda limanda during and after infection with ulcer disease

Abstract

Splenic melano-macrophage centres (MMC) and associated parenchyme structures were compared in 3 groups of dab Limanda limanda L. from the North Sea: healthy fish, fish ulcers and fish with healed ulcers still recognizable as scars on the body surface. Dab with open ulcers showed enlarged splenic MMC somewhat reduced in frequency and with increased hemosiderin content.During this stage of infection the density of pigmented granules within MMC was reduced in favour of homogeneously scattered cells or a centrally located aggregation of cels, all of which lacked phagocytic inclusions. Leucocytes were accumulated to an elevaed degree around splenic capillaries. Because of the reduced occurrence of single pigment-bearing cells in the splenic parenchyma and the very regular, rounded shape of the MMC was diminished. On the other hand, the increase in seemingly non-phagocytic leucocytes in the MMC indicates a possible argumentation of the humoral immune response. After healing of the ulcers all splenic changes accompanyng infectious conditions regressed. However, a return to the normal picture seen in healthy fish did not occur as long as scars were still visible in the skin.