1Shibushi Station, National Center for Stock Enhancement (NCSE), Fisheries Research Agency (FRA), Shibushi, Kagoshima 899-7101, 2Yaeyama Station, NCSE, FRA, Ishigaki, Okinawa 907-0451, Japan
This study addresses egg size and the relationship between seawater temperature and egg incubation period of the red frog crab Ranina ranina reared in the laboratory. Major-axis and minor-axis diameters and the volume of eggs increased from ca. 0.66 mm, 0.60 mm and 0.13 mm3 on the day of egg-laying to ca. 0.83 mm, 0.79 mm and 0.27 mm3 on one day before hatching, respectively. The incubation periods (days) of eggs from egg laying, embryonic body appearance and eye-pigmentation appearance to hatching decreased exponentially with increasing temperature. The relationships between mean seawater temperature and the egg incubation periods were analyzed using three non-linear regression models. Consequently, Belehrádek's equation and the equation from heat-summation theory fit the data well. Parameters that show the theoretical value of lower threshold temperature for egg development are ca. 16-18°C and 14-15°C in Belehrádek's equation and heat-summation theory equation, respectively.