Ance with the growth PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/26024392 superiority of hybrid grouper. Meanwhile, expressions of genes related to the protein and glycogen synthesis pathway, such as PI3KC, PI3KR, Raptor, EIF4E3, and PP1 were up-regulated, while PYG expression was down-regulated. These order SP600125 changes might contribute to increased protein and glycogen synthesis in the hybrid grouper. Conclusions: We identified a number of differentially expressed genes such as GnRH1 and GnRH3, and genes involved in GH/IGF axis and its downstream signaling pathways for protein and glycogen synthesis in Hulong Grouper. These findings provided molecular basis underlying growth superiority of hybrid grouper, and comprehensive insights into better understanding the molecular mechanisms and regulative pathways regulating heterosis in fish. Keywords: Transcriptome, PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/28388412 Growth superiority, GH/IGF axis, Hybrid grouper* Correspondence: [email protected]; [email protected] 1 State Key Laboratory of Biocontrol, Institute of Aquatic Economic Animals and Guangdong Provincial Key Laboratory for Aquatic Economic Animals, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China Full list of author information is available at the end of the article?2016 Sun et al. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.Sun et al. BMC Genetics (2016) 17:Page 2 ofBackground As economically important fish species in marine aquaculture, groupers (Epinephelus spp.) are known for their delicious taste, tender flesh and rich nutrition [1]. In the past decades, grouper industry has developed rapidly and many grouper species have been widely cultivated in China and South-East Asian countries [2, 3]. However, the sustainable development of grouper industry has been threatened by the degradation of germplasm resources and availability of grouper fries in hatcheries [4]. To resolve these problems, hybridization technology has been introduced into grouper artificial breeding. Hybridization is defined as a successful mating strategy for two species with one or more heritable traits, and is often used in artificial breeding to obtain potentially desirable traits in their offsprings [5, 6]. In grouper species, hybridization was firstly achieved between white-spotted green grouper (E. amblycephalus) and red grouper (E. akaara) [7]. From then on, more efforts have been made in developing hybrid groupers and about eight hybrids with various favorable traits, such as faster growth and development, stronger immunity and higher survival rate were obtained [8?2]. Brown-marbled grouper (E. fuscoguttatus, Efu) and Giant grouper (E. lanceolatus, Ela) are both important breeding fishes with different growth rates and disease resistance. The former is a slow growing but long-lived species with high disease resistance [13, 14], while Giant grouper is popular breeding species for its rapid growth, reaching up to 3 kg in the first year [15]. Previously, by fertilizing the eggs of Brown-marbled groupers.