Estradiol (E2) and 17 alpha-hydroxyprogesterone (17 alpha-OHP) levels exhibited
significant circadian rhythms in the prespawning phase of the reproductive cycle. Pattern of
rhythm was unimodal. Whereas, in the spawning phase E2 levels did not show significant
fluctuations in their daily cycle whereas 17 alpha-OHP levels showed significant rhythm (P
less than 0.001). Amplitude of rhythm of E2 was greater in prespawning phase while 17
alpha-OHP showed greater amplitude in spawning phase.

Abstract Oestradiol and 17α-hydroxyprogesterone (17α-OHP) levels exhibited significant
circadian rhythms in the prespawning phase of the reproductive cycle. The pattern of rhythm
was unimodal. During the spawning phase, oestradiol levels did not show significant
fluctuations, but 17α-OHP levels showed a significant rhythmic pattern of variation. The
amplitude of the oestradiol rhythm was high during the prespawning phase and that of 17α-
OHP was high during the spawning phase.