Effect of short- and long-term melatonin treatments on the reproductive activity of the tropical damselfish Chrysiptera cyanea.

Satoshi Imamura,Sung-Pyo Hur,Muhammad Badruzzaman,Dinda Rizky,Angka Mahardini,Akihiro Takemura,Yuki Takeuchi

doi:10.1007/s10695-022-01051-x

Abstract

Photoperiod plays a role in controlling the initiation and termination of reproduction in fish. Melatonin is an internal transducer of environmental photoperiod and is involved in regulating reproduction. The present study aimed to examine how melatonin impacts the transcript levels of kisspeptin (kiss1 and kiss2), gonadotropin-releasing hormones (gnrh1), and the β-subunit of gonadotropins (fshβ and lhβ) in the brain of the sapphire devil, a tropical damselfish with long photoperiod preference. Feeding mature females with melatonin-containing pellets inhibited increases in the transcript levels of kiss1, gnrh1, and lhβ within 3 h. Continuous melatonin treatment for 1 week resulted in oocyte regression and downregulation of kiss2, gnrh1, fshβ, and lhβ. When the transcript levels of kiss1 and gnrh1 were measured at 4-h intervals in the brain of sapphire devil, a day-high/night-low fluctuation was observed. The hypothalamic-pituitary-gonadal (HPG) axis may be influenced by melatonin, exerting a negative effect at night because the transcript levels of aralkylamine N-acetyltransferase (aanat2) increased during the scotophase. The expression of aanat2 was higher under short-day than long-day conditions, suggesting that there is a seasonal change in melatonin levels at night. It was concluded that change in photoperiod becomes a key factor for controlling the hormone synthesis in the HPG axis through melatonin.

Highlights

Histological observation revealed that ovaries of both groups contained vitellogenic oocytes at tertiary yolk stage (TYS) (Supplementary data 1)
Ovarian development of the zebrafish was stimulated when fish were reared in melatonin-containing water under long-day conditions (Carnevali et al 2011)
Our results support an inhibitory effect of melatonin treatment on ovarian development including vitellogenesis of the sapphire devil because feeding with melatonin-containing pellets for 1 to 2 weeks resulted in the induction of atresia and the arrest of recruitment in vitellogenic oocytes in the ovaries, as previously reported

Summary

Introduction

Melatonin levels fluctuate following a day–low/night–high cycle, which is controlled by the rate-limiting enzyme aralkylamine N-acetyltransferase (AANAT), which has a photodegradable characteristic and is affected by clock genes (Coon et al 1999; Falcón et al 2007). In addition to a daily cycle, certain fish exhibit seasonal changes to melatonin secretion according to day length (García-Allegue et al 2001; Bromage et al 2001). Seasonal change in melatonin secretion is likely an endogenous cue for the initiation and termination of seasonal reproduction in fish since melatonin levels increase during the winter months, corresponding to the longer length of the night (Porter 2000; Porter et al 2001; Bromage et al 2001). The gonadal development of the spotted snakehead Channa punctatus was inhibited after immersion in water containing melatonin, or after injection of melatonin

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Results

Conclusion