Egg size and relationship between seawater temperature and egg incubation period of the red frog crab Ranina ranina (Decapoda: Raninidae) reared in the laboratory

Abstract

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.