Methods are provided for delivery of at least one agent into egg(s) from an egg-producing aquatic animal including contacting fertilized or unfertilized egg(s) from said egg-producing aquatic animal with the at least one agent in the presence of a guanidine-containing compound capable of enhancing the permeability of the chorion of the egg(s). Methods are provided for the drug screening and compound toxicity assays. Methods are also provided for the production of reproductively sterile fish and aquatic animals for aquaculture, the aquarium trade, and control of invasive species are described. The methods include disruption of gonadal development through the administration of agents that lead to the failure of fertile gonadal development. Agents may be delivered to the eggs directly before the fertilization or post fertilization by contacting eggs in an immersion medium including the agent of interest.