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Roles of melatonin in gonadal maturation of underyearling precocious male masu salmon.

Abstract：

:Testicular maturation of underyearling precocious male masu salmon (Oncorhynchus masou) is affected by photoperiod. It is accelerated by a short photoperiod (light-dark cycles of 8:16 h; LD 8:16) and delayed by a long photoperiod (LD 16:8). Circulating melatonin levels are high during the night and low during the day:the duration of the nocturnal elevation is longer under a short than under a long photoperiod, suggesting mediation of photoperiodic signals by melatonin. This study examined whether melatonin administration mimics short photoperiodic effects and whether it accelerates the testicular development of underyearling male masu salmon reared under a long photoperiod. Fish were randomly selected in June and were divided into two groups. They were reared under LD 16:8 (lights on 04:00-20:00 h) and fed pellets sprayed with melatonin (0.5 mg melatonin/kg body weight/day) or vehicle once a day at 11:00 h until October. The plasma melatonin profile of the melatonin-treated group was similar to that expected under a short photoperiod. Melatonin treatment had a stimulatory effect on the gonadosomatic index and pituitary gonadotropin (GTH) I contents. Plasma testosterone levels were significantly higher in the melatonin-treated group than in the control group in August. However, spermiation was observed in October in both groups and no significant differences were observed in GTH II contents in the pituitary in the two groups throughout the experiment. These results suggest that mimicking a short photoperiod by melatonin administration stimulated testicular development but did not completely activate the brain-pituitary-gonadal axis in precocious male masu salmon. Thus, melatonin is suggested to be one of the factors that mediates the transduction of photoperiodic information to the brain-pituitary-gonadal axis.

journal_name

Gen Comp Endocrinol

journal_title

General and comparative endocrinology

authors

Amano M,Iigo M,Ikuta K,Kitamura S,Yamada H,Yamamori K

doi

10.1006/gcen.2000.7547

keywords:

subject

Has Abstract

pub_date

2000-11-01 00:00:00

pages

190-7

issue

eissn

0016-6480

issn

1095-6840

pii

S0016-6480(00)97547-6

journal_volume

120

pub_type

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Roles of melatonin in gonadal maturation of underyearling precocious male masu salmon.