Studies on the reproductive rhythm of fishes - XXXI. Rematuration of male goldfish under continued warm of cool temperature in combination with short or long photoperiod.

Abstract

Five groups of 2 year old goldfish were cultured at 16°C or 24°C combined with 12L or 16L or natural conditions for 12-17 months starting on June 22.Under natural condition, the males were always ready to milt except during August-September and January-March. Plasma testosterone (T) level decreased from late June and reached the lowest in August. The levels were rather high in autumn but lowered again in winter. The T level increased sharply from late March and peaked in April. Plasma gonadotropin (GtH) was low in September and December-February, but high in other months and peaked in August, October, and April.At 24°C/12L, most fish milted in September, January-March, and June when plasma T levels were high. In other months, none milted and the T levels were low. Plasma GtH fluctuated in small scales from July till February and in larger scales after March. At 24°C/16L, the males milted heavily in the first month when the T and GtH were at high levels. Thereafter, most fish did not milt, the GtH levels were low, and the T almost undtectable.At 16°C combined with 12 or 16L, the males were milting almost continuously. Plasma GtH and T were high and fluctuated several times. Their levels were mostly higher at 12L than at 16L. Key words: Male, Goldfish, Rematuration, Temperature, Photoperiod