Threshold for Synchronization of Locomotor Activity to Visible Radiation in the eel Anguilla Anguilla

Abstract

Locomotor activity of twelve small European yellow eels, exhibiting a nocturnal pattern of behaviour, was recorded in a computerized laboratory system. White light with an energy content of 20 IW cm2 in the light phase of the day synchronized the locomotor activity of all twelve eels used to the applied LD regime (LD 12:12 with a dusk and dawn period of 30 min). During a following period of constant darkness (D <10-7 1sW cm-; threshold of used radiometer) the eels lost this synchronized activity pattern and their diel locomotor activity appeared to be arrhythmic. When the animals were exposed to an LD regime again, the light phase was shifted 1800. In order to find the energy threshold for synchronization of the locomotor activity to an LD regime, the energy in the light phase was gradually raised. The following levels were used: 0.02, 0.05 and 0.09 tuW cmn2. An increasing number of eels synchronized their locomotor activity to the LD regime, from four at the low energy level to nine at the high level. When light energy of a specified narrow bandwith (548 nm A X = 16 nm) was used, one eel out of the twelve synchronized to an energy influx of 0.004 sW cm 2, equivalent to approx. 11 x 109 quanta-' cm'. An increase of the energy influx to 0.006 ILW cm2 or approx. 16x 109 quanta-' cm2 synchronized six out of the twelve. Subjected to an energy influx of longer (665-700 nm, 0.009 sW cmn2; approx. 30x 109 quanta-' cm-2) or shorter (403 nm, 0.005 ItW cm'; approx. lOx 109 quantas' cm-2) wavelengths the animals failed to synchronize. According to these findings the threshold for synchronization to radiation of 548 nm was estimated to be about 0.006 tiW cm2 and to white light 0.02 [tW cm'.