Rather than normal nucleoli, mammalian fully-grown (germinal vesicle, GV) oocytes and one-cell embryos (zygotes) contain intranuclear inclusions called "nucleolus-like bodies, NLBs" and "nucleolar precursor bodies, NPBs", respectively. Both entities remain almost inaccessible to various antibodies following standard procedure of immunofluorescence labeling that makes their protein composition and putative functions vague. Here we examine effects of molecular fixatives on the immunodetection of key nucleolar proteins in mouse NLBs and NPBs following different protocols of their fixation and post-fixation treatment. Our results show that the most impoverished for nucleolar proteins are zygotic NPBs, while only NSN-type NLBs contain all key nucleolar protein examined, including an rRNA processing factor SURF6/Rrp14. These observations support the idea that "nucleoli" of GV oocytes and zygotes have different capacities for ribosome biogenesis. The NSN-type NLBs can be involved in all nucleolar steps of ribosome production, including rDNA transcription, rRNA processing and pre-ribosome assembly. The NLBs of more mature SN-oocytes may only be capable of pre-ribosome assembly, whereas zygotic NPBs are, most likely, excluded from ribosome production.