It has been established recently that interspecific and intraspecific thoracic ganglia transplants from Penaeidae are gradually absorbed by the host without activating an encapsulation mechanism. Therefore, this research was designed to evaluate the thoracic ganglia extracts and implants from maturing Trachypenaeus byrdi (Burkenroad), Xiphopenaeus riveti (Bouvier) and Penaeus (Litopenaeus) occidentalis (Streets) females as potential inducers of sexual maturation in Penaeus (Litopenaeus) stylirostris (Stimpson), Penaeus (Litopenaeus) vannamei (Boone) and T. byrdi, from the Gulf of Nicoya, Costa Rica. Our findings suggest that interspecific and intraspecific thoracic ganglia extracts or implants from maturing penaeoid females are not capable of inducing a clear response in sexual maturation in males or females. Tissues were tested at increasing doses from 137, 386, 525 and 1500 μg g⁻¹ body weight, without any positive response. It is proposed that a hypothetical hormone, vitellogenesis-stimulating hormone, from the thoracic ganglia, is under the strong negative control of eyestalks, by the gonad-inhibiting hormone in the subgenus Litopenaeus. Therefore, the use of thoracic ganglia extracts or implants would be ineffective when compared with injecting serotonin alone, as the present results seem to support.