以組織學的方法判別日本鯷仔魚的營養狀態

Abstract

為瞭解宜蘭灣地區初孵化日本鯷仔魚的營養狀態情形以便於評估其初期死亡時做為依據，我們在日本鯷成魚來遊到宜蘭灣產卵的季節，1994年的2至4月期間分別進行六次的仔魚採樣。所得仔魚利用組織狀態的判別方法，來估算日本鯷初孵化仔魚的營養狀態。採樣之同時並進行浮游動物的調查，用以探討日本鯷仔魚的營養狀態和環境中浮游動物量變化之間的關係。除此之外，於組織狀態判別營養狀態之方法確立後，我們將本法應用於臺灣東北海域所採集的日本鯷仔魚。該仔魚係來自一條穿越黑潮、湧升流及陸棚邊緣區調查線，企圖瞭解日本鯷在不同的水體的營養情形，並比較兩地區的差異。 實驗結果顯示在宜蘭灣六次採樣中，191尾日本鯷的初孵仔魚中確有饑餓的現象發生，總體來看其饑餓率為0.54。由中腸細胞高度和體長的關係上來看，初孵化日本鯷仔魚在體長和中腸細胞高度的關係上是不會因產卵時期的先後而有所不同。而在產卵中期所採獲的日本鯷(3月14日的採樣，饑餓率為0.36)的營養狀態較產卵初期(2月23日，饑餓率為0.52)來得好。在組織狀態和浮游動物量的關係來看，發現仔魚的營養狀態和同出現的浮游動物量之間亦有相關存在(rs=-0.94,p=0.004)，而與大環境中的浮游動物量較不相關。由組織狀態之判定、中腸細胞高度之測量及初孵化日本鯷仔魚的營養狀態與同出現浮游動物之數量關係加以探討之後，其方法可以確立。 應用已確立的營養狀態判定法於東北海域不同水體中的日本鯷仔魚，結果發現在湧昇流區的日本鯷其營養狀態相當地好，平均饑餓率為0.19，而且比宜蘭灣的日本鯷是有較好的抗饑餓能力。

In this study the assessment of the early reduction of the Japanese anchovy (Engraulis japnoica) in I-Lan Bay was based on the nutritional status of the newly hatched larvae. The Japanese anchovy immigrate to I-Lan Bay to lay eggs in the spawning season. During the spawning season of 1994, from February to April, I took fortnight plankton samples, six times in total. Anchovy larvae were sorted from the samples and their nutritional status was evaluated based on the histological condition of the midgut cells. The residue of the plankton samples was used for plankton analysis. Number of individuals and dry weight of major groups of zooplankton were recorded. A relationship between the nutritional status of the larvae and the abundance of zooplankton in their immediate environment was established. I defined the nutritional status of anchovy larvae by the histological condition of the midgut cells and applied this method to study the Japanese anchovy larvae collected from a transect crossing Kuroshio, upwelling zone, and continental shelf of the East China Sea in the North Pacific off northeastern Taiwan. An attempt to study and compare the nutritional status of the Japanese anchovy from the transect and the I-Lan Bay. My results showed that among the anchovy larvae sampled from the I-Lan Bay, 54% were classified starved. No evidence was found that the time of the season when the eggs were laid had any effect on the relationship between the height of midgut cell and the body length in newly hatched larvae. Anchovy larvae caught in the mid spawning season (March 14, starved rate 36%) seemed to have better nutritional status than those caught at the beginning of the season (February 23, starved rate 52%). I found that the nutritional status of anchovy larvae was correlated with the zooplankton biomass in the same sample (r5=-0.94 P=0.004), but not with the zooplankton biomass of the environment in general. The success in the assessment of the nutritional status in newly hatched anchovy larvae by histological status, height of midgut cells, or zooplankton biomass in the same sample has confirmed that the histological methods to evaluate the nutritional status in larval Japanese anchovy are valid. When these methods were applied to the Japanese anchovy larvae from the different water mass in the North Pacific northeast off Taiwan, I found that the larvae from the upwelling zone had good nutritional status and low starved rate (19%). Their resistence to hunger was stronger than that of the larvae from the I-Lan Bay.