Temperature and reproduction in tench: effect of a rise in the annual temperature regime on gonadotropin level, gametogenesis and spawning. I. The male.

During a 9-month period (corresponding to a sexual cycle), the adult male tench, Tinca tinca, was kept in fish farm ponds receiving heated water from a power plant. In 1974, the males were submitted to three different temperature regimes: group I: ambiant temperature; group II: ambiant temperature +3 degrees C; group III: ambiant temperature + 6 degrees C. The experiment was repeated in 1975, but only using groups I and III. The reproductive cycle and thermal treatment were studied from a quantitative analysis of spermatogenesis, the duration of the spawning cycle and radioimmunoassay (RIA) measurement of gonadotropin (GTH) in plasma and pituitary, using a carp RIA system turned out to be sensitive enough to assay tench GTH, which was expressed in a c-GTH equivalent. Spermatogenesis in the tench was a discontinuous process, starting in the spring and finishing in the summer. It began earlier in heated water in which the spawning period was also considerably longer (3 months in group III against 1 month in group I). At the beginning of spermatogenesis, pituitary and plasma GTH was low, but rose rapidly when spermatogenesis was initiated (appearance of type B spermatogonial cysts and meiosis). The highest GTH levels in the blood were recorded during the spawning period, with important fluctuations probably due to discharges from the pituitary.