Rhythmic colour change of the killifish, Fundulus heteroclitus

Abstract

A photoelectric method was developed to continuously record the colour of Fundulus heteroclitus. Subsequent recording revealed the existence of an endogenous rhythm of colour change with a period of 22 h 30 min to 26 h 30 min, and an amplitude of 2.5 Ostwald units. Light–dark cycles had a masking rather than entraining effect on colour change. Temperature–salinity alterations were also ineffective in entrainment. Blinding the fish did not affect the rhythm. Hypophysectomy extinguished the rhythm of colour change, but did not affect the ability to adapt to different backgrounds.