Fish embryos may be successfully vaccinated or therapeutically treated if the therapeutic agent is injected into the yolk sac. Therapeutic agents may be directly injected or released from microspheres and enter the circulation and tissues. Injection into the yolk sac, combined with the use of carriers, allows for a continued, controlled release of therapeutic agents and processing of antigens. Fish vaccination or therapeutic treatment, selecting fish embryos post fertilization at the one-cell to eyed egg stage of develpment, and injecting the yolk sac with carriers associated with an antigen(s) or therapeutic agent(s), may be fully automated.
