The present invention provides a method of inhibiting maturation of the gonads of a juvenile animal which comprises administering to said juvenile animal an immunologically active molecule (IAM) or a vector comprising nucleic acid encoding an immunologically active molecule, said IAM being specific for a target protein within the gonads and binding thereto or causing an immune response against that target protein, and thereby inhibiting maturation of the gonads, as well as molecules of use in such methods.Se describe un método para inhibir la maduración de las gónadas en peces juveniles, tanto machos como hembras, que comprende administrar un péptido antigénico o un vector que comprende ácido nucleico que codifica un péptido antigénico, siendo dicho péptido antigénico un fragmento de una proteína blanco dentro de las gónadas, en particular un fragmento del antígeno linfocítico 75 (CD205/Ly75).
