太平洋赤道水域産キハダの外部形態について

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On the yellowfin tuna distributed in the tropical and subtropical zones of the Pacific, we made a biometrical analysis on the various morphological characters, so as to know that the fins Japanese tuna fleets are catching belong either to one population or not, based upon the specimens from 1953 to date. Samples used in this report are tabulated in Table 1, showing the origin, fishing date, number of fish, range and average of body length. All specimens were measured by the junior author at the Tokyo Central Fish Market. Measurements were made in millimeters using slide calipers and a pair of dividers in accordance with the techniques described by Marr and Schaefer (1949). Several samples of yellowfin tuna, Neothunnus macropterus, from the Equaforial Pacific ranging from 130° W to 130° E were compared on sixteen different body characters (Fig. 1) and the following results were obtained. 1) The specimens of yellowfin taken from the same area in different years show difference in maxillary length, anal length and spread caudal (Table 2). But generally we can say with certainty, they have considerably similar morphometrical characteristics. 2) It appears to be a much greater degree of separation between 170° W and 150° E and between 160° W and 130° W, than between 150° E and 130° E and between 170° W and 160° W (Table 3). 3) The specimens of yellowfin from the area of 160°W have shorter head, more anteriorly positioned ventral and pectoral fin than those form the eastward and westward regions (Table 4, Fig. 2). But for eye diameter, second dorsal and anal length, the measurement is the greatest in the Western Pacific ones and the least in the Eastern Pacific ones, and this tendency agrees with Royces result (1953). 4) By the facts above mentioned, it is morphometrically probable that there would be at least three populations rather independently but with some mixing between each other.
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太平洋赤道水域産キハダの外部形態について

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