Maternal Endocrine Factors in Early Zebrafish Development Korea

Abstract

Consistent production of viable seedstock is a critically important objective of sustainable aquaculture. Improved knowledge of regulatory mechanisms in embryogenesis could reduce early mortality and thereby contribute to more efficient fish hatchery technology. Earlier reports have shown that maternally-derived hormones deposited in yolk influence, the rate of differentiation and can alter organogenesis and viability of oviparous fish embryos and larvae. Thyroid hormones (TH) promote successful early development and survival in young fish, with actions comparable to those established in mammals, in which TH deficiencies are associated with poor performance and early mortality (Cretinism). Our experimentation tested the hypothesis that some TH actions during embryogenesis are mediated by a secondary hormone, Insulin-like Growth Factor I (IGF-1), also known to promote early tissue differentiation. To test for the presence of this possible endocrine cascade, TH actions were examined in the presence or absence of a peptide that specifically blocks IGF-1 binding to its receptor in zebrafish. Development, hatching, and larval survival were monitored in 4 groups: untreated controls, fertilized eggs immersed in the TH Triiodothyronine (T3), the IGF-1 receptor blocking peptide, or both T3 and the IGF-1 receptor blocking peptide. Expression of the IGH-1 gene was quantified with each treatment. Preliminary comparison of early events using these hatchery protocols revealed accelerated embryo development and significant induction of IGF-1 gene expression in the presence of exogenous T3, and a possible relationship of IGF-1 expression to the rate of successful hatching (R2 = 0.72). The rate of survival rate was also significantly enhanced (23.2%) in the cohort treated by T3 hormone than control. All treatment promoted survival significantly during experiment (P<0.05). The improvement in larval survival may be a result of the maintenance of elevated T3 levels through the early stage of development. Larval size was significantly decrease and increased frequency of skeletal deformities by treated with IGF-1 receptor blocking peptide. Our result also suggest interactive of both hormonal regulation (T3+ IGF-1 receptor blocking peptide) of development progress, IGF-1 receptor blocking peptide has no significant role for blockage growth and survival.