Abstract
Semen volumes and sperm concentrations of 10 Humboldt penguins kept in Niigata city aquarium were measured throughout the year. It was possible to collect the Humboldt penguins semen throughout the year, however successful trials of semen collection decreased during the molting period. Semen volumes were constantly maintained between 0.02 to 0.04ml. The average semen volume was 0.026±0.009ml. Sperm concentration sustained high levels from October to February, while the values decreased remarkably during the molting period. The average sperm concentration was 21.9±11.2 10^8/ml. As a consequence of change in sperm concentrations, it is thought that the period suitable for most reproductive of captive male Humboldt penguins is from late autumn to spring.
