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Study on the Relationship between Acoustic Backscattering Strength and Density of Larval Anchovies
鮆科仔稚魚密度與超音脈波之后方散亂反射強度之相關性
摘要
為瞭解Anchor Tag標識法之效果及其對白鰻，Anguilla japonica，之影響，利用經海水馴化之種鰻41尾，於1987年12月至1988年9月分成A（有標識且催熟）、B（有標識無催熟）、C（對照組）三組，進行標識及體長、體重等項觀測。標識後第一個月卽有絲藻附著，但號碼清晰可辨，第五個月起開始模糊。若管理良好或在大海中，絲藻附著不嚴重，則字跡應可維持半年以上。由於標識的發炎、潰爛，而引起標識籤的脫落；但如果打標識時確實植入鰻體，且環境適當，不使標識部位發炎、潰爛，標識籤應是不容易脫落的。標識籤若脫落，由於鰻魚之復原能力强，若有再捕，很難由標識的痕跡確認是經過標識之鰻魚。標識對種鰻的成長有明顯之影響，但標識部位的發炎、潰爛並不是導致種鰻死亡的主要原因。
並列摘要
A field culture experiment on adult Japanese eel(Anguilla japonica)wascarried out to investigate the efficiency of anchor tags and their effect ongrowth and survival of eel.It was conducted in a sea water pond fromDecember 1987 to September 1988.Forty one eel were divided into three groups:(A)tagged,with hormonetreatment;(B)tagged,without hormone treatment;and(C)control.Filamentous algae were found to grow on the tags one month after thecommencement of experiment when the marks on the tags were still clearlyseen.Five months latter,the marks on the tags became hardly recognizable.It is thought that the marks on the tags will last for at least six monthssince the covering of filamentous algae are less possible under a strictly controlled environment(or treated in open sea).It was found from this experiment that the tags were shed due to infections,inflammations and ulcerations of the fish.However,the tags will notbe easily shed when they were properly embedded deeply into the eel skinunder adequate environmental conditions.Taggings had an obvious effect on the eel,particularly the retardationof growth.Inflammations and ulcerations caused by tagging are not themain cause for the death of eel.