Daily rhythms of amino acid levels in the plasma of goldfish (Carassius auratus)

Abstract

1. 1. In order to determine the effect of photoperiodicity on the diurnal changes of plasma amino acid levels in the goldfish, Carassius auratus, groups of fish were maintained under short day, long day and natural day schedules for 2.5 months.

2. 2. After a 48-hr fast, five fish were killed at 3-hr intervals throughout a 24-hr period and amino acid levels were measured in plasma by a radiochemical method.

3. 3. Except for val, lys and tyr, amino acids showed circadian rhythms in at least two photoperiods. In some of these amino acids (ser, arg, asp, gln, met, leu + ile and his), changes during the day were dependent on the photoperiods, while the rhythms of others seems independent of the type of photoperiod.

4. 4. The highest value of most amino acids showing unimodal rhythm appeared at the onset of the dark phase. The bimodal change found in several amino acids may be related to reported diurnal variations of certain hormones such as corticoids and prolactin that may control these changes, as suggested for other metabolic parameters (Delahunty et al., 1978).