Off-season spawning of Eurasian perch Perca fluviatilis

This study was designed to determine the effects of the selection for body weight and of two final warming durations during an out-of-season reproductive cycle on gonad recrudescence, plasma steroid levels and spawning in Eurasian perch Perca fluviatilis males and females. Two different bodyweight classes (200-250 and 350-400 g) and two different warming periods (1 or 2 months) were studied. At the end of the chilling period, a significant effect of the selection for body weight was observed on gonad development whereas fish were the same age. According to higher levels in testosterone (12 ng mL(-1)), a better development was recorded for smaller breeders (P<0.05). A short water warming period up to 14 degrees C (1 month v.s. 2 months) allowed higher rates of females with completed gonadogenesis (33-38% v.s. 7-8%) and spawning (31-33% v.s. 0%) (P<0.05). Spontaneous out-of-season spawning (17 ribbons) and larvae were obtained. Relative fecundity was about 100 eggs g(-1) of female body weight. Five ribbons were partly fertilized with a rate ranging from 5 to 90%. These studies have shown that delayed spawning in Eurasian perch can be obtained by a temperature manipulation, but results are not sufficient because of low stimulation rate of females, low spawning rates and high heterogeneity of fertilization rates. The effects of other environmental factors like photoperiod should be tested in further experiment to improve the protocol inducing out-of-season spawning production.