ニジマスの卵の量的特性と産卵期

Abstract

1) Total weight of eggs, number of eggs, egg diameter, gonad index and their relationships with the period of spawning season were surveyed in 700 specimens of rainbow trout from six hatcheries in Honshu, Japan during the time from 1969-1971. 2) Linear relationship was observed between body weight and total weight of eggs, number of eggs, egg diameter. Egg diameter was almost independent of body weight in age group 4. Smaller specimens (both in age and in size) showed higher values of regression coefficients in all the characters. 3) Majority of the surveyed hatcheries did not show any annual variation though all the surveyed characters were found to vary over a range in every hatchery. 4) Interbatchery variation was observed in all the characters. Akashina and Okutama exhibited higher values of total weight of eggs, number of eggs and gonad index while Hiruzen exhibited higher values of egg diameter. Fujinomiya also exhibited higher values of total weight of eggs but the gonad index became less as the specimens were extraordinarily larger. 5) Total weight and number of eggs were found to vary in the early, mid and late spawning groups of the Okutama hatchery. Late spawning group exhibited higher values followed by the mid and the early spawning groups. Except Oizumi, hatcheries exhibiting lower values of the number of spots in area B (reported in the previous paper4)) showed higher values of total weight of eggs, gonad index and number of eggs. Hiruzen exhibited maximum values of the number of spots and egg diameter. All the characters exhibited intermediate values in Nikko while lower values in Oizumi.