Changes in the ovaries of adult carp

Abstract

Three series of experiments were carried out. In the first, studies were conducted on the changes occurring in the ovaries of four groups of adult female carp during a yearly cycle (between two spawning periods). Gonadal samples in vivo were taken monthly from the same marked females from August 1975 to July 1976. A portion of the samples was subjected to histological examination and the rest used for counting and measuring oocytes. It was found that changes in the adult carp ovaries during a yearly cycle consist of a gradual development of a resorption process in the oocytes after a completed vitellogenesis, the store of oocytes being progressively supplemented by those in earlier stages of development. The changes studied are not temperature-dependent and their course is similar, irrespective of whether the females had or had not spawned during the spawning season preceding the experimental period. In the second series, studies were conducted on 26 marked, mature female carp, for 5 weeks, starting on the day before artificial spawning. Gonadal samples were taken in vitro, analysed histologically, a portion being cleared in turpentine oil while others were used for in vitro culture. It was found that, irrespective of whether the females had spawned or not, they possessed oocytes after a completed process of vitellogenesis. Their response to hypophysial homogenate added to the culture medium resulted in nucleus migration. In the third series, studies were conducted on the effect of clomiphene on the ovaries. It was found that clomiphene given to mature female carp during the spawning period caused a statistically significant increase, compared to the control, in the percentage of oocytes with the nucleus shifted peripherally. However, in contrast to hypophysial homogenate injections, it failed to induce ovulation.