| Abstract |
The Allis shad (Alosa alosa L.) is a diadromous fish distributed along the coastal areas from Germany to Portugal. After approximately five years at sea, adults migrate upstream for hundreds of kilometres to reach spawning grounds in the middle and upper sections of river catchments, where they reproduce. Photoperiod is a key environmental factor, known to influence fish reproduction in temperate regions. This study examines the influence of photoperiod on the nocturnal spawning of Allis shad in the Loire River catchment (France). Results reveal a consistent spawning dynamic across the locations where it occurs in the study area, with activity beginning 1 h and 45 min before the start of dark night, peaking at 2 h after the start of dark night, and ending at 6 h after the start of dark night, with a total activity duration of 7 h and 45 min. However, variations in spawning dynamics were observed throughout the spawning season, with significant differences between long and short nights. Specifically, spawning dynamic was shorter and more intense during short nights, while it was longer and more moderate during long nights. These findings highlight the role of photoperiod in regulating the spawning dynamics of Allis shad. |