Seasonal Changes in Plasma Hormones, Sex-Related Genes Transcription in Brain, Liver and Ovary during Gonadal Development in Female Rainbow Trout (Oncorhynchus mykiss)

Huiqin Chen,Hua Rong,Baoliang Bi,Lingfu Kong,Yanhua Su,Qing Hu

doi:10.3390/fishes6040062

Abstract

The purpose of this study was to investigate the periodic seasonal changes in endocrine activity and gonadal development of female rainbow trout (Oncorhynchus mykiss) in a high-altitude cold-water environment. The fish were sampled monthly from January to November and the levels of plasma hormones (estradiol (E2), cortisol and thyroid hormones (THS)) and vitellogenin (VTG) were measured by ELISA. Moreover, the transcriptions of sex-related genes in the ovary, brain, and liver were detected by qRT-PCR. The results showed a seasonal fluctuation of plasma hormones and VTG together with the development of the ovary, which reached a peak from August to October. Similarly, the transcription of hypothalamic gonadotropin-releasing hormone-2 (cgnrh-2), hypothalamic gonadotropin-releasing hormone receptors (gnrhr) and follicle-stimulating hormone (fsh) in the brain varied from January to September, but the highest level was detected in September to November. In addition, the transcription of sex-related genes located in the ovary and liver increased significantly during August to October, accompanied by a continuous increase in the gonadosomatic index (GSI) and a decrease in the hepatosomatic index (HSI). Therefore, plasma hormones and sex-related genes regulate the development and maturation of O. mykiss oocytes with the change in seasons and peaked in November. The results of this study provide a reference for improving the efficiency of the artificial reproduction of O. mykiss.

Highlights

Reproduction is the basis of the whole ontogeny, which requires energy, ecology, anatomy, biochemistry and endocrine adaptations [1]
Sufficient information related to reproductive constant, developmental biochemistry, and molecular regulation mechanism of gonadal development are very important in aquaculture
The plasma hormones gradually increased from January to August, and peaked from August to October, which promotes the synthesis of VTG, and accelerated the development and maturation of oocytes in O. mykiss

Summary

Introduction

Reproduction is the basis of the whole ontogeny, which requires energy, ecology, anatomy, biochemistry and endocrine adaptations [1]. Sufficient information related to reproductive constant, developmental biochemistry, and molecular regulation mechanism of gonadal development are very important in aquaculture. Throughout the reproductive cycle, seasonal changes in tissue biochemical composition are related to gonadal weight, especially in females, in which the hepatic metabolism are stimulated during vitellogenesis [3]. Monthly variations in the gonadosomatic index (GSI) helps to determine the breeding season of the fish, and study of the hepatosomatic index (HSI) is important because the liver is a key organ in fish for production of vitellogenin which plays a significant role in the development of eggs [4,5]. Several studies have reported the seasonal endocrine and aromatase changes associated with reproductive activity, such as in O. mykiss [6], salmonids [7], rainbow trout (Salmo gairdneri) [8], and frog (Pelophylax esculentus) [9,10,11]

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