Kisspeptin (Kiss) and its cognate receptor, kisspeptin receptor (KissR; G protein coupled receptor 54, GPR54), have recently been recognized as potent regulators of reproduction in teleosts. Additionally, leptin plays an important role in energy homeostasis and reproductive function in teleosts. The purpose of this study was to examine differences in the concentration of the hormones of the Kiss/KissR system and leptin and the expression of their underlying genes, all of which are involved in the sexual maturation of female goldfish, Carassius auratus, following treatment with Kiss. The expression levels of KissR increased after the Kiss injection. Furthermore, the peptide hormone leptin also increased after the injection (in vivo and in vitro). Additionally, the expression of GnRH and GTHs (GTHα, FSHβ, and LHβ) increased in the brain and pituitary (in vitro and in vitro). These results support the hypothesis that Kiss plays important roles in the direct regulation of the hypothalamus-pituitary-gonad axis and leptin in goldfish. Therefore, we suggest that Kiss system gene expression is correlated with energy balance and reproduction.

Introduction
Materials and methods
    1. Study organism
    2. Kiss treatment and sampling (in vivo)
    3. Culture of liver and pituitary cells and subsequentKiss treatment (in vitro)
    4. Quantitative PCR (QPCR)
    5. Western blot analysis
    6. Plasma parameter analysis
    7. Statistical analysis
Results
    1. Time-course and dose-related effects of Kiss onKissR1 and KissR2 (in vivo)
    2. Time-course and dose-related effects of Kiss onGnRH (in vivo)
    3. Time-course and dose-related effects of Kiss onGTHs (in vivo and in vitro)
    4. Time-course and dose-related effects of Kiss onE2 (in vivo)
    5. Time-course and dose-related effects of Kiss onleptin (in vivo and in vitro)
Discussion

• Cheol Young Choi(Division of Marine BioScience, Korea Maritime and Ocean University, Busan 49112, Korea) Corresponding author
• Sung-Yong Oh(Ecosystem and Biological Research Center, Korea Institute Ocean Science & Technology, Ansan 15627, Korea)
• Young Jae Choi(Division of Marine BioScience, Korea Maritime and Ocean University, Busan 49112, Korea)
• Na Na Kim(Division of Marine BioScience, Korea Maritime and Ocean University, Busan 49112, Korea)