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It was recently discovered that double-stranded RNA (dsRNA) was a potent and specific inhibitor of gene transcription in the Caenorhabditis elegans nematode. Similar results have been reported in Drosophila melanogaster, planaria, mice, zebrafish, among other species. The interfering RNA (RNAi) phenomena occurs when a dsRNA is processed by a protein complex, specifically generating small size molecules that anneal to a target sequence of messenger RNA and promote its degradation, while also blocking its expression. The dsRNA-mediated interference is in most cases a post-transcriptional gene silencing mechanism. This paper, demonstrates that gene function can be studied in aquatic organisms by using RNA interference. Here, we describe the application of this technique in two aquatic organisms: - Zebrafish (Danio rerio), a currently relevant animal model in the field of genetics, developmental biology and biomedicine. - White shrimp (Litopenaeus schimitti), uneconomically relevant shrimp specie from the Atlantic Ocean. The function of the myostatin growth factor on growth and differentiation of muscular masses and animal growth was studied. Results demonstrated the RNA interference technology as a useful tool to study the biological function of genes involved in zebrafish development. This paper give the first evidence on growth and development of the muscular mass through hyperplasia or hypertrophy of muscle fibers as the main function of myostatin in fish, although its expression is not restricted to the skeletal muscle as is the case in mammals. Furthermore, it was demonstrated that myostatin inhibition promotes a significantly increased muscular mass phenotype. This protein is studied in several laboratories in the world searching for methods or techniques to stably inhibit myostatin. This would be a high impact result for Cuban and wordl aquaculture if it is attained in commercially relevant species. There were no previous reports in the literature on the functionality of the RNAi technology in crustaceans in vivo. Recent studies demonstrated the functionality of gene silencing in cultured shrimp cells, without further demonstrations in vivo. Our studies give the first evidence on the usefulness of dsRNA in adult shrimps in vivo. Moreover, we isolated, cloned and characterized for the first time the cDNA of the crustacean hyperglycemic hormone (CHH) of the Atlantic Ocean shrimp. Energy regulation is the primary function of this hormone in crustaceans, it is also involved in reproduction, molting, digestion, osmoregulation, and lipid metabolism in different species. The ability of the dsRNA to inhibit the function of the CHH in shrimps was also studied. [ABSTRACT FROM AUTHOR]