天草周邊に於ける重要生物の資源學的研究II.カタクチイワシに関する研究

Abstract

The present papar is based on the measurements of Japanese anchovy, Engraulis japonicus Temminck & Schlegel, carried out at Tomioka, Amakusa, from September in 1946 to February in 1948. The fishing season of the said species is extending from January or February to October or November at the mentioned districts. It measures from 40mm to 120mm in total length, but it does not increase in size uniformly according to the advancement of the season. Judging from the degree of maturity of gonad, the spawning season of this species seems to be twice in a year around Amakusa, one corresponding to the latter part of May, while the other to the beginning of November. The average number of vertebrae for each group (containing a urostyle) is whithin a range from 44.93±0.0774 (S. E.) to 45.68±0.1060. Further, it shows a minimum in April, while it becomes maximum in July. The coefficient of variability of to ?? al length, C (=σ×100/M; M, mean total length in mm; σ standard deviation), indicates a rather complicated seasonal variation, but it becomes minimum twice during the season, namely in the beginning of May and in the latter paat of August. The values of k and n in a formula, W=kLn (W, body weight in g; L, total, length in mm), are 1.75×10-6 and 3, 267 respectively. When n is made equal to 3.267, the value of k for each group is whithin a range from 1.46×10-6 to 2.10×10-6. Such a value of k bears some relation to the total length, being low between 80mm and 90mm. Further, it shows a seasonal variation, being high in March and October, while low in July. This seasonal variation of k is considered to be mainly affected by the maturation of gonad or spawning.