New cool research from Wagner et al. that despite the lack of “day” and “night”, deep-sea fish experience daily cycles. What is the trigger? Diurnal changes in bottom currents corresponding to tidal fluctuations. The below graphs shows current direction and velocity on deep-sea floor in the NE Atlantic Ocean indicating 12.5 hour tidal cycles.
The researchers followup by measuring pineal and retinal melatonin in two bottom-dwelling fish, a grenadier Coryphaenoides armatus and a deep-sea eel Synaphobranchus kaupii(below). They additionally quantified the release of melatonin in cultures of isolated pineal organs and retinae in S. kaupii.
Synaphobranchus kaupii, Cambraia Duarte, P.M.N. (c)ImagDOP
Both fish exhibited signs or synchronicity an periodicity in melatonin implying an ‘internal clock’ (figure below, click for larger). Furthermore, peak values correspond to the beginning of the lunar day and night with lower values during the second half of lunar day and night and during moonrise and moonset. The researchers suggest that fish “perceive these cyclic cues with the help of their lateral line system and use this information as an alternative to
photic stimuli to synchronise the various endogeous oscillators to the physical environment.”