“…Histochemical, immunocytochemical, and biochemical studies have demonstrated that pineal cells in these species contain the indoles, 5-hydroxytryptophan, 5-hydroxytryptamine (serotonin) and melatonin (Falcon et al, 1980(Falcon et al, , 1981Fenwick, 1970 b ;Hafeez and Zerihun, 1976 ;Meissl et al, 1978 ;Owman and Rudeberg, 1970 ;Vivien-Roels et al, 19811 Quay, 1970 ;Weber, 1974, 1976). Levels of these compounds and protein content fluctuate over daily light : dark cycles (Birks and Ewing, 1981 b ;Falcon et al, 1980 ;Meissl et al, 1978 ;Weber, 1974, 1976 (Fenwick, 1970 b), and the killifish (de Vlaming et al, 1974) ; the effects generally depending upon the time of year and photoperiod. On the basis of these observations, it would be important to determine the effects of various photoperiod-temperature regimes on circadian rhythms of indoles and their related enzymes.…”