Chromosome Behavior of Meiosis-inhibited Eggs with Cytochalasin B in Japanese Pearl Oyster

Abstract

For efficient induction of triploid pearl oyster, the effect of cytochalasin B (CB) treatment on meiosis and fertilization of eggs in Japanese pearl oyster Pinctada fucata martensii was investigated. CB treatment (0.1 mg/l) was initiated at 5 min after insemination for 10 min (CB 1) or initiated at 15 min after insemination for 15 min (CB 2). In CB 2, two groups of chromosomes at anaphase of second meiosis became two female pronuclei at 33 min after insemination due to the lack of second polar body formation. In CB 2, 51.1 % of eggs had two female pronuclei and one male pronucleus at 33 min after insemination. Chromatin of these three pronuclei gradually condensed and became metaphase chromosomes for first cleavage. Eggs with three pronuclei seemed to develop into triploid embryos. In CB 1 the percentage of eggs with three pronuclei was lower (16.6% at 33 min) than that of CB 2. In CB 1 we classified abnormal chromosome behavior of eggs into following typical two types: (1) both first and second polar bodies formation was inhibited. Eggs formed four or five pronuclei. (2) At anaphase of first cleavage one pronucleus derived from second polar body was still observed. The percentage of these abnormalities was higher in CB 1 than in CB 2. © 1990, The Japanese Society of Fisheries Science. All rights reserved.