Le contrôle environnemental et hormonal de la reproduction du barbeau, Barbus barbus (L.) et du chevaine, Leuciscus cephalus (L.) (Pisces cyprinidae), en captivité

The barbels and the chubs are reared in heated water (20-25 °C) and under natural or controlled photoperiod. The female barbels can ovulate spontaneously 15 times (maximum) during a reproductive season (January-July). The female chubs ovulate (after hypophysation) 2 times (perhaps 3) in a year (January and May-July). The distribution of intraovarian oocytes of female barbels, just after ovulation, is quadrimodal (including primary oocytes, oocytes with vacuoles, vitellogenetic oocytes and ova). The ovarian structure of the chub, just after hypophysation is trimodal (including primary oocytes, oocytes with vacuoles and ova). When barbels are submitted to an annual photoperiodic cycle contracted to 6 months (2 cycles in a year), two reproductive periods are observed (January-May and September-November). This phenomenon is certainly the consequence of the inhibiting effect of a decreasing photoperiod on the sexual maturity of both males and females. The maturity of female and male barbels (previously maintained under 10L/14D or 16,5L/7,5D) remains a longer time under 6L/2D/2L/l 4D or 6L/8,5D/2L/7,5D than under 8L/16D. Under constant photoperiod (8L/16D), the reproduction of the barbels begins spontaneously but, the average number of spawnings for each female decreases and the reproductive periods are shorter. In natural water temperature (in tank) the female barbels spawn two times during the reproductive period (June-July). While reproducting, the somatic growth of the barbels is low, sometimes nul or negative (loss of weight). Somatic growth begins once reproduction is ended. It seems that some females are more efficient. In female barbels the period between two successive ovulations is characterized by high E2 levels (> 300 pg/ml) and a sinusoidal variation of these E2 levels. There is a significant linear correlation between the testosterone levels and the gonadosomatic index in the males. The thyroxine (T4) concentrations of the males and females are low during reproduction. They are high outside reproductive periods. The opposite is noticed for the plasma triiodothyronine (T3) concentrations. The barbels exhibit a spontaneous and synchronized expelling of sexual products if there is a spawning substrate.