Effects of Photoperiod and Temperature on Gonadal Activity in the Cyprinid Teleost, Notemigonus Crysoleucas

The effects of various photoperiod-temperature regimes on gonadal activity in the cyprinid teleost, Notemigonus crysoleucas, were examined during several different phases of the annual reproductive cycle.2. Regardless of the time of year when the experiment is initiated a long photoperiod-warm temperature regime stimulates gonadal development to the prespawning condition or induces spawning. Neither a warm temperature alone nor a long photoperiod alone will stimulate final gonadal maturation.3. Notemigonus is not "refractory" to long photoperiod-warm temperature gonadal activation during the postspawning season.4. Short photoperiods in combination with warm temperatures cause gonadal regression in this species. A low temperature-short photoperiod regime does not induce gonadal involution.5. Spermatocyte formation and proliferation as well as the early phases of vitellogenesis occur independently of environmental factors. Final gonadal maturation and the rate of gametogenesis, however, depend on specific environmental conditions.