Ovarian Cycling of Japanese Barracuda Sphyraena Japonica in Northeastern Taiwan Waters

Abstract

布氏銀带鰶（Encrasicholina punctifer Flowler，1938）與島嶼銀带鰶（Stolephorus insularisHardenberg，1933）為淡水河口仔稚魚羣聚中的主要優勢種類。為瞭解其在河口域生態系中所扮演的角色，於1989年10月～1990年10月，每月在淡水河口以流袋網利用漲潮時採集標本，由腸胃內含物與發育階段及消化道形態之關係來探討其攝食策略。結果發现，這兩種鯷魚在初期生活史階段食性很類似，為嗜浮游生物性。主要餌料生物種類為浮游矽藻與橈脚類，其次為浮游性藍綠藻與綠藻、原生動物、介形類、短尾類與長尾類幼生、端脚類、藤壺幼生、軟體動物二枚貝的幼生、箭蟲、尾索類住囊蟲科的幼生與魚卵等。胃部形態隨著發育階段而改變，後期仔魚期為字型，稚魚期為字型，幼魚期為字型。各發育階段之攝食選擇偏好性之差異很大，在腸胃道形狀由直線形轉為曲線形時，食性急速變化；食性從植物性浮游生物轉為動物性浮游生物。食性轉換時空胃率發生的頻率較高。文中並探討兩種鯷魚在個體發生過程的食性之變化與食物資源分割利用之關係。The feeding strategy of the larvae of two dominant species,Encrasicholinapunctifer Flowler 1938 and Stolephorus insularis Hardenberg 1933,in the estuary ofTanshui River was studied based on the monthly sampling by using a modifiedcommercial set net during day-time flood tide from October 1989 through October1990.Their larvae are planktivorous.The dominant diets found in their stomachcontents were diatom and copepoda,followed by blue-green algae,green algae,protozoa,branchiopoda,malacostraca,Balanus sp.,mollusca,chaetognatha,proto-chordata,and fish eggs.The morphology of stomach patterns changed withdevelopmental stages,i.e.,I-type in postflexion larva,V-type in juvenile,andY-type in young fish,respectively.The diet of the fish changed significantly withtheir ontogenetic developmental stage.Dramatic change appeared during theperiod when intestinal pattern changed from linear to loop types,in which dietchanged from phytoplanktivorous to zooplanktivorous,and the frequency ofstomach empty rate also increased at this period.The ontogenetic diet shift inrelation to food resource partition is also discussed.