マダイ人工放流魚と天然当歳魚の外部形態の比較〔外部形態によるマダイ人工放流魚と天然当歳魚の比較と識別-1-〕

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The present study aims at finding the differentiation of hatchery-reared and artificially-released red sea bream from wild fish, based upon their morphometric differences. A total of 80000 hatch-ery-reared red sea bream fry, ranging 40-60mm FL, were fin-clipped and released at three locations in the coastal waters of Hirado island, Nagasaki Prefecture in 1980 and 1981. Experimental Gochi trawlings were carried out at the three locations seven times three months after releasing each year, yielding 1011 artificially-released red sea bream (hereafter referred to aftificial fish) and 1177 wild fish of age O. Morphometric measurements were done on fork length and 14 other characters. Regression lines of each of the latter on the former for artificial fish and wild fish were compared by means of covariance analysis. The results obtained were given below: 1. Body height. height at eye, eye diameter and upper jaw length were smaller in artificial fish than in wild fish of the same size. 2. Length of the longest dorsl fin spine, length of pectoral fin, length of caudal fin and length of ventral fin spine showed lower values in artificial fish than in wild fish at the time of releasing and for a short time after that. About a month later, however, however, no significant difference was seen in length of any fins between two groups of the fish, suggesting that artificial fish adapted themselves to wild surroundings.
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