A transgenic non-human aquatic organisms, such as piscine, crustacean, mollusks, and the like, having a transgene which results in disrupting the production of and/or activity of growth differentiation factor-8 (GDF-8) chromosomally integrated into the germ cells of the aquatic organism is disclosed. Also disclosed are methods for making such organisms and nucleic acid sequences encoding GDF-8 polypeptides from such aquatic organisms.