Age-Specific Reproductive Characteristics in Fishers

Abstract

We studied the age-specific reproductive characteristics of 29 male and 43 female captive fishers (Martes pennanti) during 1991–1993. Length of baculum was shorter in yearlings than adults, but changed little in length after the first 15 months of life. Adult (>18 months old) and yearling (6–18 months) males were nonreproductive June-January based on low concentration of testosterone and regressed testes. Testes were smaller in yearlings than adults, but there was no difference between age classes in level of testosterone in blood, number of sperm, and concentration of sperm. Concentration of testosterone began to increase in December for adults and in January for yearlings, followed by an increase in testicular size that reached a maximum in March and April for adults and yearlings, respectively. Maximum production of sperm for both age classes occurred March-May. Concentration of testosterone began to decrease in April and testes were fully regressed and production of sperm ceased by June. Adult and yearling females were anestrus June-March. Size of vulva was different among yearlings, nonpregnant adults, and pregnant adults. Vaginal cornification was lower in yearlings and concentration of progesterone in blood was higher in pregnant adults than the other groups of females. Cornification of adults was >90% by 7 days postpartum and remained >90% for 3–5 weeks. Only three of 16 yearlings exhibited cornification >90%. Mean postimplantation development was 36 days. Concentration of progesterone peaked in pregnant females during February corresponding with implantation.