[Nucleic acid and ribonucleoprotein status during early development of fish embryos (Salmo irideus and Salmo trutta fario)].

1. The total amount of nucleic acids as well as DNA and RNA were analysed biochemically in embryos of the troutsS. irideus andS. trutta fario from cleavage to early differentiation stages. In the same developmental stages ribonucleoprotein (RNA and basic protein) was investigated cytochemically at different embryonic regions. The phase of gastrulation was of main interest. 2. The results of both methods show that the quantity of RNA and ribonucleoprotein increases beginning with themorula stage. The maximum is reached in theblastula. 3. When during the blastoderm stage RNA and basic protein are stained histochemically a characteristic gradient of intensity can be determined. From the increase of RNA and basic protein in periblast and blastoderm and from the gradual staining effect itself one can conclude that RNA and basic protein is transported from the yolk through the periblast into the embryo. There should exist atransfer of substances possibly as ribonucleoprotein particles. The limited time of this transfer during early embryogenesis shows that this phenomenon is not the result of energetic yolk utilization but it is connected with the following differentiation processes. 4. After injection of actinomycin D into the blastocoel development is stopped at the beginning ofgastrulation. Therefore a new synthesis of messenger RNA should be necessary for further development. 5. The ribosomal RNA is constant duringgastrulation but the amount of basic protein decreases in this time. During neurulation and the beginning differentiation phase a new increase of RNA takes place but now the quantity of basic protein does not change. 6. In contrast to investigations of the Urodele development in the trout embryo no change of RNA and basic protein is found during gastrulation in the invaginating material and the covering neuroectoderm. Therefore no transfer of substances takes place between the two blastemas. There are many differences in the embryonic development of Urodela and Teleosts. Nevertheless in both classesa relation between the yolk system and the embryonic blastema results in the beginning of thedifferentiation processes. This results point to the possible morphogenetic importance of the yolk system.