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Daily age and growth of juvenile grey mullets Mugil cephalus in the Tan-Shui River Estuary as revealed from otolith microstructure
|Publication Year :||1997|
結果發現，烏魚耳石日週輪的形成具有日週性，由日週輪的數目可推算日齡。除了日週輪之外，也發現次日輪、副核心、第二成長區及首次攝食輪等記號，這些記號容易混淆日齡的估算。淡水地區烏魚稚魚的出現季節為11月中旬至翌年的3月下旬，其加入群數不止一個。加入的最小平均體長為20.56mm（日齡約32天）：遊出體長為34.00mm（日齡約62天）。稚魚在河口域停留的時間為1個月左右，此時的成長率為0.452 mm d^(-1)。由稚魚日齡所逆推的產卵期約在10月至翌年2月，換言之，淡水地區的烏魚稚魚，並非完全來自11月下旬至l月下旬的洄游產卵群。
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.
|Appears in Collections:||漁業科學研究所|
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