RT Journal Article T1 Interplay between the endocrine and circadian systems in fishes A1 Isorna Alonso, Esther A1 Pedro Ormeño, Nuria de A1 Valenciano González, Ana Isabel A1 Alonso Gómez, Ángel Luis A1 Delgado Saavedra, María Jesús AB The circadian system is responsible for the temporal organisation of physiological functions which, in part, involves daily cycles of hormonal activity. In this review, we analyse the interplay between the circadian and endocrine systems in fishes. We first describe the current model of fish circadian system organisation and the basis of the molecular clockwork that enables different tissues to act as internal pacemakers. This system consists of a net of central and peripherally located oscillators and can be synchronised by the light–darkness and feeding–fasting cycles. We then focus on two central neuroendocrine transducers (melatonin and orexin) and three peripheral hormones (leptin, ghrelin and cortisol), which are involved in the synchronisation of the circadian system in mammals and/or energy status signalling. We review the role of each of these as overt rhythms (i.e. outputs of the circadian system) and, for the first time, as key internal temporal messengers that act as inputs for other endogenous oscillators. Based on acute changes in clock gene expression, we describe the currently accepted model of endogenous oscillator entrainment by the light–darkness cycle and propose a new model for non-photic (endocrine) entrainment, highlighting the importance of the bidirectional cross-talking between the endocrine and circadian systems in fishes. The flexibility of the fish circadian system combined with the absence of a master clock makes these vertebrates a very attractive model for studying communication among oscillators to drive functionally coordinated outputs. PB Bioscientifica SN 0022-0795 YR 2017 FD 2017-03 LK https://hdl.handle.net/20.500.14352/18025 UL https://hdl.handle.net/20.500.14352/18025 LA eng NO Ministerio de Economía y Competitividad (MINECO) DS Docta Complutense RD 2 may 2024