Retinal light input is required to sustain plasma melatonin rhythms in Nile tilapia Oreochromis niloticus niloticus

Abstract

The aim of this work was to confirm previous findings suggesting that the eyes are required for night-time melatonin production in Nile tilapia and further characterise this divergent circadian organisation. To do so, melatonin levels were firstly measured in eyecups and plasma to determine circadian patterns of melatonin production.Secondly, the effect of partial ophthalmectomy on the suppression of melatonin production was determined in vivo as well as ex vivo pineal light/dark sensitivity.Finally, to investigate whether such findings could be related to post-surgery stress, melatonin analyses were performed in the subsequent 24 h and 7 days postophthalmectomy with cortisol levels assessed as an indicator of stress. Our results showed an inverse pattern of melatonin production in the eye cups of tilapia compared to blood circulating levels, suggesting different roles played by melatonin in these two tissues. Results then demonstrated that total or partial ophthalmectomy resulted in the suppression of night-time melatonin production. Furthermore, although pineals in culture were shown to be photosensitive, night-time melatonin levels were much lower than seen in other species. Finally, when performing sampling immediately or one week post-surgery, no difference in the melatonin profiles were observed. It is therefore unlikely that post-surgery stress would explain such suppression in melatonin production although all fish displayed high cortisol levels most probably due to social and handling stress. Taken together, these results provide further evidence of a new type of circadian organisation in a teleost species where the eyes are required to sustain night time melatonin levels. Section: Regulatory systems

Effect of LED light spectra on circadian rhythms in goldfishCarassius auratus: expression profiles following thermal stress

“…These results were similar to the in vivo results. This is in agreement with Martinez-Chavez and Migaud (2009), who reported that the pineal organ of the Nile tilapia Oreochromis niloticus niloticus was photosensitive and, when placed in vitro, increased night-time melatonin levels. We hypothesize that the observed increase in ZT16 and 40 means that photosensitivity was stimulated in the night-time as culture time passed.…”

Current knowledge on the photoneuroendocrine regulation of reproduction in temperate fish species

“…These two models, however, are only based on the pineal gland and do not consider the potential integrated role of the retina as is seen in other vertebrates. When this is taken into account and work on tropical species such as O. niloticus , O. mossambicus and C. gariepinus is included, then at least three models can be proposed from a pineal‐centred system in salmonids to a mammalian‐like centralized organisation in O. niloticus and C. gariepinus (Migaud et al , 2007; Martinez‐Chavez et al , 2009; Nikaido et al , 2009). In these later species, melatonin production was shown to rely predominantly on photic information perceived by the eyes.…”

Moonlight affects mRNA abundance of arylalkylamine N‐acetyltransferase in the retina of a lunar‐synchronized spawner, the goldlined spinefoot

“…Because in mammals, the photic information is transduced by a photoneuroendocrine network composed of the retina, suprachiasmatic nuclei (SCN), and pineal gland (Falcón et al, ; Migaud et al, ), the input of environmental illumination through the eyes appears to be an essential route. In some tropical teleost species such as the Nile tilapia Oreochromis niloticus and African catfish Clarias gariepinus , photic information perceived by the eyes has a predominant impact on melatonin production (Migaud et al, ; Martinez‐Chavez and Migaud, ). Moreover, the pineal gland and eyes are necessary for sustaining the full amplitude of plasma melatonin rhythms in the European seabass and Atlantic cod Gadus morhua (Bayarri et al, ; Migaud et al, ).…”