Studies on the melano-macrophage centres of seabass, Dicentrarchus Labrax, and seabream, Sparus aurata, from two fish farms in Malta

Abstract

In the present work, the distribution and histochemical nature of melano-macrophage centres in the spleen, kidneys and liver of clinically abnormal seabass (Dicentrarchus labrax), and gilthead seabream (Sparus auratus), collected from two fish farms in Malta, was studied. Starvation experiments were also conducted. The results demonstrate that melano-macrophage centres in sea bass which survived a VNN outbreak were not significantly affected, possibly due to the acute nature of the disease. In sea bream, the results suggest that tissue catabolism is a major factor contributing to the formation of the pigments within melano-macrophages. During the starvation experiments, the melano-macrophage centres had increased after 6 weeks and 10 weeks of complete deprivation of food. These results indicate that increased deposition of melano-macrophage centres was clearly associated with cachexia; there was less clear correlation with other clinical symptoms such as fin erosion and swollen abdomen. After ten weeks of starvation, haemosiderin is observed mostly in the melano-macrophage centres of the spleen, with no deposition being noticed in the kidneys. This work has confirmed that the splenic melano-macrophage centres of seabream are the sites where iron derived from effete red blood cells is stored as haemosiderin for possible eventual re-utilisation. The melano-macrophage centres were entirely absent from the liver of all specimens.