Histoarchitectural variations during Oocyte growth in rainbow trout (Oncorhynchus mykiss)

Abstract

During the present study changes in gonadsomatic index and hepatosomatic index in different reproductive phases of rainbow trout Oncorhynchus mykiss has been worked out. This study represents detail description of histological variations during developmental stages of ovarian follicles. In this study, oocyte growth has been described in 7 stages Chromatin-nucleolus, Perinucleolar, Cortical alveolus, Primary vitellogenesis, Secondary vitelliogenesis, Maturation and Spent phase. The mean oocyte diameter increased from 183.5µm at perinucleolar phase to 2249.5µm in maturation phase, and nuclear dimensions changed from 73.5 µm in perinucleolar phase to 184 µm in secondary Vitellogenic stage. During this dramatic increase in the ooplasm and follicle wall revealed a numerous changes in morphological characteristics like nuclear extrusion, alveoli formation, vitelliogenesis, and variations in thickness of zona pellucida. These morphological changes in growing oocyte have been discussed in relation to various physiological factors, including endocrine, exocrine and environmental cues.