Reviews in Fish Biology and Fisheries 11: 321–330, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
A review of the multifunctional hormone melatonin and a new hypothesis
Marine Biology Center / Institute of Oceanology of Polish Academy of Sciences, sw. Wojciecha 5 Str., 81-347
Gdynia, Poland (E-mail: email@example.com)
Accepted 29 July 2002
Abstract page 321
One hormone – numerous effects 321
Melatonin in ﬁsh – physiological approach 322
Melatonin – a new factor contributing to osmoregulation in terrestrial vertebrates? 323
Melatonin – a factor contributing to osmoregulation in ﬁsh? 324
Preliminary results: melatonin binding sites in gills and kidneys of rainbow trout and ﬂounder
Interactions with other hormones
Conclusions and perspectives 327
Key words: ﬁsh, homeostasis, hormones, melatonin, osmoregulation, pineal organ
The pineal hormone melatonin is a potent regulator of seasonal and circadian rhythms in vertebrates, among them
ﬁsh. Melatonin synthesis shows a diurnal rhythm with higher levels at night. In recent years, the pineal gland and
its major product gained a number of attributes suggesting their role in integration of various neural and endocrine
functions. Besides the well-established physiological effects mediated via high-afﬁnity cell membrane receptors
belonging to the superfamily of G-protein – coupled receptors, melatonin reveals direct intracellular actions.
This paper attempts to synthesise the physiological roles of this multifaceted hormone in ﬁsh. The use of higher
vertebrates paradigms (considering every limit in interpretation) was essential due to lack of satisfactory data on
ﬁsh. The actions of melatonin in major organs responsible for osmoregulation in ﬁsh are discussed. The inﬂuence of
melatonin on water/ion excretion by affecting the circulatory blood hemodynamic and by interrelations with other
hormones systems engaged in water/ion homeostasis are considered. New data providing the ﬁrst evidence for the
presence of melatonin binding sites in ﬁsh gills and kidneys are presented. The paper suggests a new approach that
may lead to an improved understanding of osmoregulation processes.
One hormone – numerous effects
Melatonin (N-acetyl-5methoxytryptamine) came to
scientiﬁc attention as a potent agent for blanching in
frog skins in the late 1950s (Lerner et al., 1958).
The indole hormone is primarily synthesised and
secreted by the pineal gland in all classes of verteb-
rate. In all species examined, melatonin production