STUDY OF THE REPRODUCTIVE-CYCLE OF THE GUDGEON, GOBIO-GOBIOL .3. MATURATION OF GONADS UNDER OVULATORY AND SUB-OVULATORY TEMPERATURE REGIMES

The effects of ovulatory (20-degrees-C) and sub-ovulatory (15-degrees-C) temperature conditions on breeding performance were investigated in captive gudgcon, Gobio gobio L. Breeders were reared in controlled temperature and photoperiod conditions in order to accelerate gonad maturation and produce off-season spawning. Gonad maturation was determined monthly by morphometric and cytological examination of oocytes sampled in vivo. During the spawning season, ovulation was induced by hormonal treatments with carp pituarity extracts (10.0-mu-g/g body weight). The effects of temperature were evaluated in terms of percentage of mature fish, number of induced and spontaneous ovulations, pseudogonadosomatic index and egg production. This study indicated that rearing breeders at a subovulatory temperature (15-degrees-C) elongates the spawning season (99 versus 57 days at 20-degrees-C), increases the percentage of mature and ovulated females and reduces the rate of spontaneous ovulations (10 % versus 52 %), limiting in ovario regression and loss of sexual products.