TESTICULAR AND SOME HORMONAL CHANGES DURING THE 1ST 4 YEARS OF LIFE IN THE MIRROR CARP, CYPRINUS-CARPIO L

Male carp bred in outside ponds in Poland were sampled monthly from 5 to 46 months old, to analyse changes in gonadosomatic index (GSI) and pituitary gonadotropin hormone (GTH) in blood serum and in pituitary, 17α20β8P and 11KT in blood and gonadotropin releasing hormone (GnRH) in pituitary and hypothalamus. First signs of puberty with significant testis development (a high GSI of 12% and strong mitotic activity of the type‐B spermatogonia) were seen at 13 months and 4548° days. By 16 months the GSI had declined to 6%. At 25 months the GSI remained at 6%, active spermatogenesis was observed, with some accumulation of spermatozoa but no spermiation. During the years 4 and 5 the GSI increased regularly from 6 to 12% and spermiation was observed nearly all the time. Some GTH was found in the blood before gonad development occurred. Thereafter there was no major change in GTH (10–20 ng ml−1 serum) except a peak of 200–130 ng ml−1 at 38. 39 months: this peak was not related to any major biological event, except that all fish reached spermiation at that time. A progressive increase of the amount of GTH in the pituitary was observed during the sampling period. Opposite fluctuations in the GnRH content were observed in brain and pituitary. Circulating 11‐ketotesterone (11‐KT) increased to 20 30 ng ml−1 serum in spring 22–25 months and at 36–37 months in parallel with the progressive rise of the water temperature, but independently of stage of testes development. These peaks of 11‐KT were followed immediately (1984) or two months later (1983) by temporary major rises of 17αa‐hydroxy‐20β‐dihydroprogesterone reaching 2–3 ng ml1 serum; this was not related to the temperature nor to the spermatogenetic stage. Copyright © 1992, Wiley Blackwell. All rights reserved