Factors influencing ovulation in the Mexican axolotl as revealed by induced spawnings

Axolotl females may be induced to spawn by injecting them with small doses of FSH prior to mating. Data on the different categories of spawnings obtained by this procedure have established the following points. (1) Spawnings of injected females completely without fertile eggs are small (173 eggs average). Courtship occurred in some of the matings (spermatophores found) but not in all. Spawnings of injected but uninseminated females re-mated with a second (or third) male, not becoming inseminated, but all having some eggs fertilized by contact with spermatophores (showing courtship) are likewise small (219). It can be concluded that courtship of the injected female, even by two successive males, does not stimulate ovulation of additional eggs. (2) Insemination of injected females induced additional ovulation more or less frequently, depending upon whether the female was inseminated by the first, or a subsequent male with whom she was mated. Insemination by the first male, within 15 hours after the female had been injected with FSH, resulted in stimulation of ovulation in 36 of 54 spawnings (67%). The 36 spawnings averaged 593 eggs per spawning. In contrast, insemination by a second or third male, more than 15 hours after the female was injected with FSH, resulted in stimulation of additional ovulation in only 4 of 21 spawnings (19%). (3) Survival time of spermatozoa in inseminated females has been established. Considerable numbers of spermatozoa capable of fertilizing eggs survive for about one week. A few survive for 11 to 12 days, but none was found after 14 days.