The Role of Thyroid Hormone in Fish Development with Reference to Aquaculture

Abstract

Recent progress in an understanding of the role of thyroid hormone (TH) on fish development was reviewed with particular reference to fish farming. TH is a small liposoluble hormone produced in thyroid follicles and has two bioactive forms, tetraiodothyronine (thyroxine, T 4 ) and triiodothyronine (T 3 ). Mother fish deposits a considerable amount of TH in developing oocytes. The amount of TH and ratio of T 3 to T 4 in eggs vary among species and stocks of the same species. The role of TH in eggs is not yet clear, though enhanced survival and growth of embryos and larvae by the enrichment of the eggs with TH have been reported in some cases. On the other hand, the role of TH that promotes larvajuvenile transition or metamorphosis has been established in teleost fish. The level of TH elevates at the onset of metamorphosis, and the treatment with TH can induce precocious metamorphosis. Considering the TH role in fish development, the disorder of its proper function could lead to deformity in juveniles, which is frequently observed in hatchery. In addition, many environmental chemicals have potential disrupting TH function in developing embryos and juveniles of fish.

Progesterone and norgestrel alter transcriptional expression of genes along the hypothalamic–pituitary–thyroid axis in zebrafish embryos-larvae

“…However, NGT administration altered the transcription of Trh gene at 48 and 96 hpf, which implies that the production of thyroid stimulating hormone (encoded by Tshb gene) is independent of thyrotropin-releasing hormone (encoded by Trh gene) during the early development of zebrafish. These results are in accordance with the previous report that the secretion of thyroid stimulating hormone is controlled by thyrotropinreleasing hormone in mammals and birds, but not effective in fish (Yamano, 2005).…”

“…It is well known that thyroid hormones elicit specific physiological effects by binding to nuclear receptors (Thra and Thrb) and play a pivotal role in fish development (Yamano and Miwa, 1998;Yamano, 2005). Thus, transcriptional expression levels of Thra and Thrb genes were determined as indicator for circulating thyroid hormone levels.…”

Effects of persistent organic pollutants on the thyroid function of the European sea bass (Dicentrarchus labrax) from the Aegean sea, is it an endocrine disruption?

“…In fish, thyroid status is positively correlated to reproductive status, whereas a seasonal rise in thyroid hormones coincident with gonadal maturation and reproduction has generally been observed. During ovarian maturation, thyroid hormones accumulates in the developing oocytes where they play a significant role in fish embryogenesis (Power et al, 2001;Yamano, 2005). Small thyroid follicles appear first at early stages of the larval period, then the follicles increases gradually in number and size.…”

“…Small thyroid follicles appear first at early stages of the larval period, then the follicles increases gradually in number and size. These small follicles are able to produce thyroid hormones which are detectable in larval fish in low concentrations (Yamano, 2005). During this phase the thyroid hormones intervene in the transformation of larvae into juveniles (Power et al, 2001).…”

Assessing reproductive and endocrine parameters in male largescale suckers (Catostomus macrocheilus) along a contaminant gradient in the lower Columbia River, USA

“…Thyroid hormones are important for early development and somatic growth in juveniles and adults of some teleost species (Yamano, 2005;Carr and Patiño, 2011), but PBDE effects on thyroid function have been inconsistent for this group of vertebrates (Torres et al, 2013). Plasma T4 levels in male LSS ranged from undetectable (LOD, 2.5) to 10.4 ng/ml, and plasma T3 from undetectable (LOD, 0.7) to 9.1 ng/ml.…”