A rapid ex utero development, optical transparency and many fluorescent reporter transgenic lines that allow specific in vivo labelling of cell lineages or organs are among the most important reasons why the zebrafish (Danio rerio) has become a widely used model organism in the field of developmental biology. Besides, many studies using zebrafish have demonstrated that most developmental processes and the molecular pathways controlling them were conserved between zebrafish and mammals. The development of the hematopoietic system makes no exception to this rule: similar to mammals, hematopoiesis in the zebrafish happens in two sequential waves that eventually lead to the development of the main blood cell lineages also found in mammals, such as erythrocytes, myeloid cells and lymphoid cells, from multipotent precursors known as hematopoietic stem cells. In the present work, we focused our attention on two transcripts of unknown function si:ch214-211p16.1 and si:ch214-211p16.2 that are enriched in emerging hematopoietic stem cells. We inquired about the function of these two genes during embryonic definitive hematopoiesis by overexpressing them or suppressing them without drawing any relevant conclusion about their function. However, the study of the fluorescent reporter transgenic line p16.1:GFPLT in the adult zebrafish, in combination with other fluorescent reporter transgenic lines, allowed to gain better insights on the adult zebrafish hematopoietic system. Indeed, the p16.1:GFPLT transgene allowed the discrimination between brain macrophages and microglia by immunohistochemistry. But most importantly, the p16.1:GFPLT transgene brought our attention to a population of B-cells that express mpeg1, a gene originally described as macrophage-specific in the zebrafish model. Not only there are two subsets of B-cells, one expressing mpeg1 and the other not, but also this finding proves that the mpeg1 promoter cannot be considered as macrophage-specific as soon as B-cells are present in the fish, i.e. in juveniles and adults therefore questioning many studies that have been published in the last decade.