Daily Rhythmic Expression Patterns of Melatonin Bio-synthesizing Genes in Zebrafish (Danio rerio) Testis in Response to Altered Feeding Condition

The alternation of light (L) and darkness (D) cycle is the most important zeitgeber (“time giver”) of the circadian system. Still, feeding time also acts as a potent synchronizer of the teleost circadian system. In fish, the impact of the altered photoperiodic condition is known, but the impact of altered feeding cycles in the daily rhythm of fish circadian system is largely unknown. The objective of this work was to explore how 12 hr shift in feeding time alters expression of genes concerned with melatonin synthesizing enzymes in zebrafish testis tissue. In this study, zebrafish maintained under a 12 hr light-12 hr darkness were fed at light phase (ZT03 and ZT10) in normal feeding (NF) group and another one was the altered feeding group (AF) fed at dark phase (ZT15 and 22) for 30 days. Daily rhythms of expression of genes concerned with melatonin synthesizing enzymes and circulating melatonin level were studied. The 12 hr shift in scheduled feeding induced a phase delay of 4-5 hr in the acrophases in the case of aanat2, 10-11 hr for asmt and 4 hr for aanat1 but a slight shift seems to exist in case of tph1. Serum melatonin levels showed a significant daily rhythm in both condition but displayed phase delay in AF condition. Rhythmic expression of aanat2 and peak at midnight corresponds with the high concentration of melatonin during the night. Melatonin is a multi-potent molecule; the change in the rhythmic expression of its bio-synthesizing enzyme genes through altered feeding time may lead to desynchronization in the physiology.