An electron microscopical study on the genesis of lipofuscin, melanin and haemosiderin in the haemopoietic tissues of fish

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Abstract
The mode of origin of the pigments within the macrophages of the haemopoietic tissues of some fish species was studied with the electron microscope. Lipofuscin appears to be derived from damaged cellular components, such as effete mitochondria, through the peroxidation of their unsaturated lipids. Haemosiderin is almost certainly derived from the breakdown of haemoglobin from effete erythrocytes. Melanin appears to be derived from phagocytosis of melanin granules or their precursor organelles from melanin‐containing cells. Both lipid peroxidation and haemoglobin breakdown produce free radicals and cations which are potentially toxic. Melanin absorbs free radicals and has strong affinity for cations and it is probable that they are neutralized by the melanin in macrophages. The electron micrographs published here illustrate the association of the lysosomal apparatus with pigment formation in fish melano‐macrophages. These findings appear valid for all the species examined and may apply to all fish. It has been suggested that fish melano‐macrophage centres represent primitive analogues of the germinal centres of higher animals. This study reveals that melanocyte‐like cells outnumber melano‐macrophages in the kidney of rainbow trout, Salmo gairdneri. Moreover, like melano‐macrophages, these cells increase markedly in number during starvation.