Summary
Drawing on work with passerine birds, investigations on the self‐selection of photoperiod in a constant environment by pumpkinseed sunfish (Lepomis gibbosus) capable of controlling their lighting have been carried out. Each aquarium with lighting equipment was set up in a separate, light‐tight compartment in a quiet, constant‐temperature room. Under one treatment, an overhead fluorescent light could be turned on and off by breaking a photobeam. Under two further treatments, breaking the photobeam turned the light on for three minutes. Fish were fed daily at a regular hour. The latter two treatments, but not the first, resulted in data containing diurnal rhythmic components as analyzed by autocorrelation techniques. The results are discussed in the context of different methods of measuring “internal clock” mechanisms.
Methodology
The apparatus was located in a quiet, windowless, steady temperature (21°C) room. A plywood box contained 4 separate, light-tight compartments (Fig. 1) each with an aquarium measuring 51 x 27 x 32 cm high. The lid of each compartment was fitted with a viewing port and a Sylvania F475/CW 40W fluorescent light unit, with the heat-generating ballast mounted on the outside, and connected to recording and switching circuitry. (The constancy of the temperature was established prior to the treatments using a Bristol Dynamaster temperature recorder.) Gravel covered the bottom of the aquarium, and a filter in the aquarium released compressed air. The water level in the aquarium was renewed weekly with distilled water.