Effect of temperature and photoperiod on sexual maturation and spawning of the common carp: II. Under conditions of low temperature

Abstract

Carp were reared at a constant cool temperature (16°C) combined with either short (12L–12D) or long (16L–8D) photoperiods. The fish showed similar, continuous increases in the number of matured oocytes and body weight increment during the first 5–6 months (August–January). Loss of matured oocytes and a reduction in body weight, probaly indicating repeated partial spawnings, were observed from time to time commencing in February. These changes became more significant after 9 months. Fish ovulated one month earlier at 16L–8D than at 12L–12D later changed to 16L–8D. Fish from the long photoperiod group spawned totally when the temperature was raised to 22°–25°C, while fish of the short photoperiod group ovulated at 20°–24°C. Photoperiodism is probably involved, although slightly, in ovarian maturation even under cool temperatures.