AGE-SPECIFIC REPRODUCTIVE CHARACTERISTICS IN FISHERS

We studied the age-specific reproductive characteristics of 29 male an d 43 female captive fishers (Martes pennanti) during 1991-1993, Length of baculum was shorter in yearlings than adults. but changed little i n length after the first 15 months of life. Adult (> 18 months old) an d yearling (6-18 months) males were nonreproductive June-January based on low concentration of testosterone and regressed testes, Testes wer e smaller in yearlings than adults, but there was no difference betwee n age classes in level of testosterone in blood, number of sperm, and concentration of sperm. Concentration of testosterone began to increas e 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 fo r both age classes occurred March-May. Concentration of testosterone b egan to decrease in April and testes were fully regressed and producti on of sperm ceased by June, Adult and yearling females were anestrus J une-March, Size of vulva was different among yearlings, nonpregnant ad ults, and pregnant adults, Vaginal cornification was lower in yearling s and concentration of progesterone in blood was higher in pregnant ad ults than the other groups of females, Cornification of adults was > 9 0% by 7 days postpartum and remained > 90% for 3-5 weeks. Only three o f 16 yearlings exhibited cornification > 90%. Mean postimplantation de velopment was 36 days. Concentration of progesterone peaked in pregnan t females during February corresponding with implantation.