Day-night behavior in river entry of kutum and its relation to melatonin

Abstract

Reproduction in most fish species is a scheduled phenomenon and spawning occurs at a precise time ensuring maximum survival of offspring. During the spawning season, reproductive activities of fish species and their daily entry to rivers are influenced by environment. Number of Rutilus frisii kutum entered a river discharging to Caspian Sea was analyzed to investigate the association between timing of river entry and day–night changes in environmental variables. Four thousand five hundred and sixty seven ascending adult kutum were collected in Khoshkrood River between March and May 2012. Physicochemical parameters were recorded and Melatonin levels were measured in a hundred migratory kutum over day and night during the spawning period. A significant effect of daytime on river entry was observed, as more fish entered the river at night. Melatonin levels decreased to the minimum level during peak days of migration, suggesting variations in melatonin levels can help to harmonize the daily rhythm in kutum migration.

Keywords:

• Melatonin
• Rutilus frisii kutum
• circadian
• photoperiod
• movement

Acknowledgments

We are grateful to Shahid Ansari Hatchery Complex staff members for their generous help with animal collection, especially Ahmad Ghanaat parast. In addition, special thanks must go to Akbar Nasrollahzade for providing constructive advice and Khayam Delafkar for his helpful endeavors while sampling period.