Development of a broodstock of Arctic charr was undertaken in experimental tanks supplied with water pumped from Lake Léman (Geneva) at a depth of 36 metres. Spawners were subjected todifferent thermal regimes to determine the effects of temperature on spawning time and gameteviability. In the tanks, the ovulation occurred spontaneously at the same time as the wild fish in the lake. The timing of ovulation was slowed down at 8 °C and above. At 11 °C, ovulation was inhibited. When the water temperature of the rearing tanks was higher than 5 °C for several weeks prior to spawning, the quality of eggs produced by reared females was poorer than those of wild fish because the process of overripening was very rapid above 5 °C. Provided that spawners were reared at 5 °C and examined twice a week to detect ovulation, 80 to 90 percent survival to the eyed stage could be expected for eggs of reared females. The fertilization rate of eggs produced by spawners transferred from 8 to 5 °C in December was high (78%). When the transfer occurred in January, the viability of ova tended to decrease (63%).

The results of preliminary experiments in the development of a hatchery brood stock of whitefish of Lake Geneva, Coregonus shinzi palea Cuv. and Val. (lavaretus), are described. Factors likely to influence the date of spawning and the quality of eggs were studied by reference to the performance of wild spawners from the Lake Geneva. Fish were reared in tanks and the ovulation of females occurred spontaneously at the same spawning time as in wild spawners from the lake. Reared females have produced 30 000 eggs/kg against 45 000 in wild fish. The survival rate of a domestic egg was about 10% less than that of wild females. Since the overripening of the ova was rapid it was necessary to check the ripe females twice a week. The exposure of fish to long days in autumn delayed spawning by two months and permitted the synchronization of hatching under optimal conditions of growth. The ovulations were spread over a period of 3 months when the fish were subjected to long days until spawning. In contrast, termination of the long day regime in December induced a synchronization of the ovulations over just one month.