Effect of Density, Sex Ratio, and Refractory Period on Spawning of the Mud Crab Rhithropanopeus Harrisii in the Laboratory

Abstract

Adult mud crabs, Rhithropanopeus harrisii, were held in the laboratory for 14 months at densities of 20 or 40 crabs per 0.5 m2 and at female: male ratios of 2:1, 4:1, and 6:1. Females spawned for 9 months during the calendar year and entered a refractory period from November through January. Field populations in North Carolina spawn for only 5 months of the year. Spawning increased with increasing crab density and female: male ratio. Ovigers were most abundant in habitats containing 40 crabs at a 6:1 sex ratio (8.3 ovigers per week), and were least abundant in habitats containing 20 crabs at a 2:1 ratio (2.8 per week). However, the highest proportion of crabs spawned in habitats containing 20 crabs at a 6:1 sex ratio. Neither density nor sex ratio affected female mortality. Crabs at the lowest sex ratio (2:1) and highest density (40 crabs) produced larvae that survived poorly (45% survival to first crab stage). However, larval viability was good at all other densities and sex ratios. Maintaining crabs at high densities and female: male sex ratios in the laboratory, even during a portion of the nonbreeding season, augmented egg production. These methods can facilitate studies of reproduction and development of R. harrisii.