Study of the somatropic hormones expression during the early development of thick lipped grey mullet (Chelon labrosus)

Abstract

Mullets are considered as potential species for sustainable aquaculture due to their feeding characteristics. Among all the mullets found in the Spanish territory, Chelon labrosus is having higher commercial interest because, in comparison to the rest, it reaches larger sizes in a shorter period of time. Recently hatched larvae go through a series of molecular, biochemical and morphological changes during growth and development to juveniles. Some of the processes involved in larval development, including the growth hormone (GH) and insulin-like growth factor I (IGF-I), are subjected to endocrine control. With the purpose of deepening the knowledge of the possible factors involved in the early development and differentiation in this species, expression of the two somatotropic genes, gh and igf1, was studied during the first 92 days of life using real time PCR. These genes showed different expression patterns. The expression of gh increased significantly, reaching to its maximum at 43 days post hatch (dph), and decreased drastically afterwards, maintaining relatively low levels during the rest of the studied period. However, igf1 showed a gradual raise, peaking at 50 dph, and maintaining thereafter relatively constant levels. Moreover, the maximum growth rate, between 22 and 54 dph, coincides, to a large extent, with elevated expression levels of gh and the beginning in the increase of igf1 observed in this work. This can suggest that gh and igf1 are expressed in an independent manner during the first 50 days of life, while the GH/IGF-I axis starts to be functional afterwards.