EFFECTS OF PHOTOPERIOD AND TEMPERATURE ON TESTICULAR DEVELOPMENT IN MALE AYU, PLECOGLOSSUS-ALTIVELIS

Growth, gonadosomatic index and plasma steroid profiles in male ayu, Plecoglossus altivelis, cultured under short/long photoperiods and cool/warm temperatures were determined. Juvenile males were assigned to each of four different photoperiod/temperature regimes (16 L/18-degrees-C, 16 L/24-degrees-C, 8 L/18-degrees-C and 8 L/24-degrees-C) at random. Fish were killed and examined bi-weekly over the following 16 weeks. Mean body weight in the 16 L/18-degrees-C treated fish was the highest among four treated groups. No significant differences between body weights of the 16 L/24-degrees-C, 8 L/18-degrees-C and 8 L/24-degrees-C treated groups were observed. Ayu in the 8 L/18-degrees-C treated group had the highest values of gonadosomatic index, plasma testosterone (T) and 17-alpha-hydroxyprogesterone (17-alpha-OH P). No significant differences of plasma E2 were observed among the treated groups. In the 8 L/18-degrees-C and 8 L/24-degrees-C groups, peak levels of 17-alpha-OH P occurred after 12 and 14 weeks of treatment, respectively. No peak levels of plasma T and 17-alpha-OH P were observed in 16 L/18-degrees-C or 16 L/24-degrees-C treated ayu. Spermiation occurred only in ayu with 8 L/18-degrees-C treatment. The data suggest that testicular development in ayu is temperature and photoperiod dependent: short photoperiod and cool temperature favour gonadal development.