Search

The plasma profile of growth hormone (GH) was monitored in the freshwater catfish, Clarias batrachus over a single 24-h transverse timescale in the middle of each month starting from March to August. This period included different physiological status of the fish and also varying environmental photoperiod and ambient temperature. Statistically significant ultradian rhythm in GH was detected in all the months of study. Of the two ultradian peaks, one was located invariably in the early photophase with the other one in the early scotophase. During the period of intense reproductive activity (June and July), circadian rhythm in GH was also recorded in addition to ultradian rhythm. The 24-h average (Mesor) and amplitude of ultradian rhythm of GH were high in March and April coinciding with the increase in photoperiod, temperature and feeding activity. Mesor increased further in May, reaching the maximum in June with a further rise in the water temperature and intense gonadal activity, but the amplitude declined during these months. In the breeding month of July, Mesor declined moderately and amplitude declined further. In August, Mesor and amplitude both attained minimum levels. In July and August one of the ultradian peaks overlapped with the circadian peak of the GH rhythm and the circadian peaks appeared in the night, while in other months it appeared in the early morning or at midday. Synchronization of one of the ultradian peaks with that of the circadian peak in GH in the night of July and August might provide physiological advantage for the execution of breeding at the coolest part of the day. The rhythmic patterns of GH secretion might have a strong correlation with the changing photoperiod, temperature, and feeding and reproductive activity. The observed temporal organization in GH in C. batrachus may have physiological consequences that might provide suitable milieu for the regulation of its somatic and gonadal growth, and execution of reproductive activity. [ABSTRACT FROM AUTHOR]

Analysis of changes in the plasma levels of GTH II over a 24-h day/nightcycle revealed statistically significant circadian or ultradian variationor both in its circulating level during the gonadally active months of thereproductive cycle. The 24-h average and amplitude of circadian or ultradianrhythm in GTH II increased with the advancement of ovarian development andmaturation. In April, a single peak in GTH II level was noticed in the nightat 20.6 h. In contrast, in May, June and July a biphasic pattern (ultradianrhythm) was noticed with two characteristic peaks, one in the photophase andthe other in the scotophase. In addition, in May a statistically significantcircadian rhythm in plasma GTH II was validated with a peak located at 20.1h. These rhythms seem to have physiological significance. The ultradian rhythmwith two peaks during the reproductively active phase appears to provide asuitable physiological milieu for the temporally different yet synchronouspopulation of oocytes for the secretion of steroids. Thus, the observed temporalorganization in GTH II may have physiological consequences leading to accomplishmentof reproductive process at appropriate time of the year. [ABSTRACT FROM AUTHOR]

In the present investigation, daily variations in plasma levels of melatonin,testosterone and estradiol-17β were analysed in the tropical freshwatercatfish, Clarias batrachus during early and late-preparatory, pre-spawning,late-spawning and post-spawning phases of its annual reproductive cycle. Plasmamelatonin levels exhibited a significant circadian rhythm during all the reproductivephases but peaks were invariably at night. The amplitude of melatonin washigh during the early-preparatory phase and low in the pre-spawning phase.Testosterone also displayed significant rhythm during all the studied phasesexcept post spawning phase. Estradiol-17β revealed diurnal rhythm onlyduring preparatory and pre-spawning phases. The peak in the levels of plasmatestosterone and estradiol-17β were recorded during the photophase. Duringthe late-preparatory phase, the rhythm of testosterone coincided with therhythm of estradiol-17β. [ABSTRACT FROM AUTHOR]