Inducing Effects of Hormones in Metamorphosis-arrested Grouper Larvae

Abstract

Recently, we obtained some metamorphosis-arrested larvae of king grouper (Epinephelus lanceolatus) from a private hatchery. The larvae had reached normal juvenile sizes and ages; however, they remained in larval period and had a translucent appearance with elongated dorsal and ventral spines. Histological study indicated that the abnormal larvae have fewer follicular cells in the thyroid than do normal larvae. We immersed the abnormal larvae in triiodothyronine (T3, 0.01 and 0.1 ppm), cortisol (0.1 ppm), or both hormones (0.01 ppm T3+0.1 ppm cortisol). The results showed that the larvae immersed in T3 and T3+cortisol entered the juvenile period, whereas the ones immersed in cortisol alone did not. Additionally, no significant synergistic effect of cortisol and T3 was observed in this experiment. Based on these data, we concluded that thyroid hormone is the major regulatory hormone in grouper metamorphosis. While cortisol may enhance the metamorphosis-inducing effect of thyroid hormone, it is completely ineffective in the absence of thy roid hormone.