寄生性橈足類Caligus macarovi感染西北太平洋秋刀魚之研究

Parasitic Copepod Caligus macarovi Infection on Pacific Saury in the Northwestern Pacific Ocean

秋刀魚（Cololabis saira）是一種在北太平洋表層洄游之重要經濟性魚類。本研究分析在2009年台灣秋刀魚漁業漁季中5月（漁季先期）、6-7月（漁季初期）及8-11月（漁季主期）等三時期漁獲物秋刀魚遭寄生性橈足類Caligus macarovi感染之盛行率、平均感染強度及豐富度，及其與魚體肉體長、體重及肥滿度間關係。研究結果顯示，秋刀魚遭C. macarovi感染之盛行率，由5月開始之81.6%，至6-7月下降爲68.3%，再下降至8-11月的51.1%。平均感染強度及豐富度之變動趨勢與盛行率相同，分別由5月開始之3.38及2.76，至6-7月下降爲2.66及1.81，再下降至8-11月的2.40及1.23。在肉體長與體重上，在8-11月中遭寄生者顯著小於未遭寄生者，且此時期之寄生蟲數量頻度分布在肉體長與體重上均呈現雙峰分布，其分界處分別約在29-30cm與130-140g。同時，秋刀魚肉體長與體重僅在8-11月時會與C. macarovi寄生蟲數間呈現顯著負相關性，但在5月與6-7月時之相關性不顯著。肥滿度對寄生蟲之盛行率、平均感染強度及蟲數間之相關均不顯著。綜言之，在2009年漁季主期之8-11月中C. macarovi感染西北太平洋秋刀魚之盛行率可能約在50%左右，並且該盛行率會受到秋刀魚季節性洄游之漁獲月份與漁場位置（經緯度）所影響。

Pacific saury (Cololabis saira) is a migratory pelagic fish, one of the important target species in the North Pacific fisheries. During three saury fishing periods of May (pre-fishing period), June-July (initial fishing period), and August-November (main fishing period), 2009, we investigated prevalence, mean intensity, and abundance of the parasitic copepod Caligus macarovi infected on the fish in catches of the Taiwanese saury fishery, and examined their relationships with fish's knob length, body weight, and condition factor. The prevalence was 81.6% in May, decreased to 68.3% in June-July, and decreased further to 51.1% in August-November. The mean intensity and the abundance had the trends similar to that of the prevalence. They were, respectively, 3.38 and 2.76 in May, decreased to 2.66 and 1.81 in June-July, and further deceased to 2.40 and 1.23 in August-November. The knob length and body weight of the infected fish were significantly smaller than those of the un-infected in August-November, expressed by the frequency distribution curves, each with two peaks separated at the boundaries of 29-30 cm and 130-140g, respectively. Also, the numbers of the parasites infected were significantly, negatively correlated with the length and the weight in August-November but not in May and June-July. The condition factor was not significantly correlated with the prevalence and mean intensity of the infection, and the number of the parasites infected. It was concluded that in the 2009 fishing season, the prevalence of the C. macarovi infected fish might be around 50% during the main fishing period of August-November. The prevalence changed with month of the fishing and location (latitude-longitude) of the fishing ground due to the fish migration.