The ovarian cycle durations observed in this study differed
from those previously reported for sirenian species.
Nascimento (2004) observed mean cycles of approximately
23 days in Amazonian manatees, and Larkin (2000) and
Horikoshi (2004) observed a high variation of the cycle
duration (ranging from 9 to 42 days) in their studies of
Florida manatees. Our results did agree with those reported
for dugong (56
±
8.6 days; Wakai et al., 2002), although the
procedure for the definition of ovarian cycle duration may
have been one of the factors responsible for the variation
observed by those authors. Nascimento (2004) reported
the use of the interval between fecal estrogen peaks as
a reference for cycle calculation. Considering the proximity
of cycle length reported by the author and the interval
between the two different estradiol peaks observed in our
study (23.33
±
9.20 days), the author may have considered
the interval between these two peaks as one complete
cycle. Horikoshi (2004) and Larkin (2000) defined the ovarian
cycle as an increase in fecal estrogen followed by an