| Summary: | 碩士 === 國立臺灣大學 === 漁業科學研究所 === 85 === Grey mullets Mugil cephalus are not only important coastal
or inshore species but also very desirable aquaculture species
in Taiwan. Adults migrate to the southwestern coasts of Taiwan
for spawning during late November through the following late
January. However juveniles are captured from early November in
the coastal estuaries. These phenomena indicate the
disagreement in the period between adults spawning and juveniles
occurrence. For understanding the disagreement, the periodicity
of daily growth increments deposited in otoliths of juvenile
grey mullets was validated by using tetracycline immersion.
Then, daily age and growth of the juveniles collected in the Tan
- Shui River Estuary during the periods from November 1995
through March 1996 and from November 1996 through March 1997
were determined by growth increments in otoliths. Spawning
period of the juvenile grey mullets was backcalculated from
their daily age. Except the daily growth increments, several
remarkable checks like sub - daily growth increments, accessory
primordia, secondary growth zones and first feeding check were
found in the otoliths. The juvenile grey mullets arrived the
estuary at the size of 20.56 mm mean TL (approximately 32 days
after hatching), left the estuary at 34.00 mm (62 days). The
duration of estuarine staying was about a month, growth rate was
0.452 mm d-1 during this period. The juveniles in the estuary
were composed of multiple cohorts. Backcalculated spawning
period lasted approximately five months from October through the
following February. This indicated that the juveniles collected
in the Tan - Shui River Estuary were not completely originated
from the migratory spawning stock in the coastal waters off
southwestern Taiwan.
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