Keeping track of time under ice and snow in a sub‐arctic lake: plasma melatonin rhythms in Arctic charr overwintering under natural conditions

Abstract

Although photoperiod is considered as a major environmental cue for timing of seasonal events in fish, little is known about the photic information perceived by fish in different aquatic environments. The strongly seasonal Arctic charr, Salvelinus alpinus, reside in lakes covered by thick ice and snow throughout the dark winter in the north. In the present study, we have measured diel changes in their plasma melatonin concentrations from September to June in Lake Storvatnet (70 degrees N), northern Norway. In addition, we have measured the in vitro melatonin production of Arctic charr pineal glands held at experimental light conditions. From September to April a diel profile in plasma melatonin was seen in the charr in Lake Storvatn, with highest concentrations at night. This profile reflected the prevailing above-surface photoperiod, even in February when there were minimal changes in sub-surface irradiance between day and night. In June, plasma melatonin was low throughout the 24-hr cycle, despite there being a marked sub-surface difference in irradiance between night and day. At this time the irradiance in night probably remained above the threshold for suppression of melatonin production. The in vitro experiments revealed no endogenous rhythm in the pineal melatonin secretion, supporting the conclusion that the diel profile seen in the Arctic charr in their natural habitat was driven by ambient photoperiod. In conclusion, the Arctic charr appear to keep track of time even under the extreme conditions of high latitudes during winter, when lakes have thick ice and snow cover.

Unique arylalkylamine N-acetyltransferase-2 polymorphism in Salmonids and profound variations in thermal stability and catalytic efficiency conferred by two residues

“…A previous study has indicated an effect of season on the amplitude of plasma melatonin surge in the Arctic charr (Strand et al, 2008). This, together with in vitro studies indicating temperature impacts on pineal AANAT2 activity (Benyassi et al, 2000;Falcón et al, 1996) that temperature may act directly on the Arctic charr pineal gland to regulate melatonin secretion.…”

“…Each challenge lasted for 90min and was preceded by 30min incubation at 5°C. At each step the medium was collected and stored at −20°C until melatonin was quantified using a validated radioimmunoassay as described previously (Strand et al, 2008).…”

“…Species of the family Salmonidae are migratory teleosts and their perception and anticipation of seasonal changes in the AANAT2 diversity and function in salmonids environment are crucial. In contrast to other teleost species, they lack a functional circadian clock in the pineal gland (Falcón, 1999;Iigo et al, 2007), yet in vitro and in the wild they exhibit daily melatonin rhythms that mirror exactly the prevailing day length throughout the year (Gern and Greenhouse, 1988;Strand et al, 2008). Temperature modulates the amplitude of the nocturnal surges in AANAT2 activity (Falcón, 1999) and melatonin secretion (Max and Menaker, 1992), and has also been suggested to be a driving signal of salmonids' biological rhythms because the seasonal changes in the amplitude of the nocturnal melatonin surge correlate with the ambient temperature changes (Strand et al, 2008).…”

Persistence, Entrainment, and Function of Circadian Rhythms in Polar Vertebrates

“…Diagram for reindeer adapted with permission from Macmillan Publishers, Ltd. (127). snow cover; yet, melatonin rhythms are abolished during the polar day (121). However, because light exposure directly inhibits release of melatonin by the pineal, persistent melatonin rhythms could also result from masking.…”

The role of winter phenology in shaping the ecology of freshwater fish and their sensitivities to climate change

“…For example, studies of several species in both Norway (Strand et al 2008) and Finland (Jurvelius and Marjomaki 2008) have shown that diel behaviour patterns driven by day-night cycling continue unimpeded in waters covered by thick layers of ice and snow. Successful feeding in reduced light can be achieved by improving vision or by employing other senses that do not depend on light (e.g.…”