Response of a neotenic goby,ice goby (Leucopsarion petersii), to thyroid hormone and thiourea treatments

In order to clarify the mechanisms of neoteny in the ice goby (Leucopsarion petersii), we examined effects of thyroid hormone and thiourea (TU) treatments on their neotenic characteristics and the pituitary-thyroid axis. Adult ice goby were exposed to 3, 5, 3'-triiodothyronine (T3, 0.1 ppm), TU (inhibitor of thyroid hormone synthesis, 30 ppm), or the combination of the two for 2 weeks. Observations of whole body T3 levels, thyroid follicles and TSH immunoreactive cells in the pituitary suggests the presence of a functioning thyroidal system. However, all of the neotenic features did not disappear in T3-treated fish, suggesting the absence of T3 responsiveness in peripheral tissues. These results indicate the similarity between neoteny of the ice goby and obligatory-type neoteny of urodeles.