3462 | wileyonlinelibrary.com/journal/are Aquaculture Research. 2019;50:3462–3470. © 2019 John Wiley & Sons Ltd 1 | INTRODUCTION Larval development in fish involves tissue organizer activity and pat‐ terning followed by organ differentiation, the rate and success of which are influenced by thyroid hormones (THs) and the insulin‐like growth factor (IGF) signalling pathway (Eivers, McCarthy, Glynn, Nolan, & Byrnes, 2004). Maternally derived THs transferred to fish embryos act as regulatory compounds as yolk is absorbed. This trans‐generational signalling pathway has been referred to as ma‐ ternal provisioning (McComb, Gelsleichter, Manire, Brinn, & Brown, 2005). The primary goal of this study was to examine possible inter‐ actions of the TH and IGF pathways. The zebrafish, Danio rerio, has been identified as a critically im‐ portant model for genetic and endocrine studies with applications throughout finfish aquaculture (Ribas & Piferrer, 2013). Due to the ready access to DNA sequence data and commercially available nucleic acid polymers, this species was chosen for our study of genetic and endocrine regulation of early development. Abundant stores of maternal THs are found in unfertilized zebrafish eggs, and the genes required for the thyroid signalling pathway are expressed very early in zebrafish development (Campinho, Saraiva, Florindo, & Power, 2014). The somatotropin/IGF‐1 and pituitary/thyroid axes are fre‐ quently presented as separate regulatory signalling pathways (e.g. Reinecke, 2010; Zhu et al., 2017), but their developmental actions are not isolated. IGF‐1 has been shown to promote peripheral monodeiodinase activity, leading to enhanced conversion of less biologically active thyroxin (T 4 ) into triiodothyronine (T 3 ) in mam‐ mals (Hussain et al., 1996; Lartey, Werneck‐de‐Castro, O‐Sullivan, Unterman, & Bianco, 2015). The generalized notion that T 3 regulates Received: 10 April 2019 | Revised: 10 July 2019 | Accepted: 4 August 2019 DOI: 10.1111/are.14305 ORIGINAL ARTICLE Thyroid hormone‐induced swim bladder and eye maturation are transduced by IGF‐1 in zebrafish embryos Mohammad Habibur Rahman Molla 1 | Md T. Hasan 2,3 | Won J. Jang 2 | Cesar D. Soria Diaz 1 | Patrick Appenteng 1 | Haliliy Marufchoni 1 | Bushra Jahan 4 | Christopher L. Brown 1 1 World Fisheries University Pilot Programme, Pukyong National University (PKNU), Busan, South Korea 2 Department of Biotechnology, Pukyong National University (PKNU), Busan, South Korea 3 Department of Aquaculture, Sylhet Agricultural University, Sylhet, Bangladesh 4 Biotechnology and Genetic Engineering Discipline, Khulna University, Khulna, Bangladesh Correspondence Christopher L. Brown, World Fisheries University Pilot Programme, Pukyong National University (PKNU), 45 Yongso‐ro, Nam‐gu, Busan 48513, South Korea. Email: brownchristopher38@gmail.com Funding information World Fisheries University Abstract Maternally derived thyroid hormones (THs) deposited in yolk promote fish embryo‐ genesis and survival, and understanding early regulatory mechanisms could lead to improved seedstock production. We have tested the hypothesis that some thyroid actions may be mediated by insulin‐like growth factor I (IGF‐1), another promoter of embryo development. Differentiation and performance were assessed in embryos treated with THs in the presence or absence of an IGF‐1 receptor blocking peptide. Treatment with the TH triiodothyronine (T 3 ) promoted IGF‐1 gene expression at days 1 and 5, and advanced swim bladder and eye development, but blocking the IGF‐1 receptor eliminated the swim bladder and eye effects. Growth and survival at 1 week of age were impaired by the IGF‐1 receptor blocking peptide alone, but concurrent treatment with T 3 partially restored these indices. Our results confirm interaction of T 3 and IGF‐1 regulatory signalling in zebrafish embryogenesis and transduction by IGF‐1 of thyroid‐driven swim bladder and eye maturation. KEYWORDS embryo, hormones, insulin‐like growth factor 1, T 3 , thyroid, transduction, zebrafish