In captive Heterobranchus 1ongifilis females, oocytes maturation and ovulation are induced by a single injection of human chorionic gonadotropin (hCG) at a dose of 1.5 I.U./g body weight. In the present study, three experiments were performed in order to specify the timing of ovulation and the effects of varying latency period on the quantity and quality of the collected ova. The ova quality was estimated by hatching percentage and proportion of deformed larvae obtained after artificial fertilization. The results showed that, in an individual female, ovulation of postvitellogenic oocytes is not synchronous and takes 3 to 4 hours to be completed, between 7–8 h and 11 h after hCG injection at 30 °C. The quantity of ova that could be collected by handstripping increased with the latency period, from 18,000 ± 12,000 to 72,000 ± 29,000 ova per female at 8 h and 11 h after injection, respectively. However, the first ova obtained (8 h after injection) were of good quality (94% hatching) and showed no signs of incomplete final maturation. Eleven hours after injection, the percentages of ovulated oocytes within the whole ovarian population of postvitellogenic oocytes were high in all the females, being generally around 90%. After ovulation, aging of ova occurred rapidly: the proportion of deformed larvae increased significantly (from 4 to 20%) 2 h after completion of ovulation and, 4 h post-ovulation, hatching percentage dropped from 92 to 36%. In H. longifilis, the optimal latency period can be defined as the time, from injection to stripping, allowing the best compromise between quantity and quality of ova released. This latency period was found to be 11 h following hCG injection at 30 °C, and corresponds approximately to the completion of ovulation.

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.