Development of an efficient, noninvasive method for identifying gender year-round in the sea urchin Paracentrotus lividus

Identification of sex in the sea urchin, Paracentrotus lividus, has thus far been achieved through gamete analysis, often using lethal, stressful and generally invasive methods. In this study, we developed a noninvasive technique to identify the sex of P. lividus based on the secondary sexual characteristics of genital papillae. This method was evaluated with fully and nonfully sexually mature individuals that were collected during both reproductive and nonreproductive seasons. Each individual was examined under a stereomicroscope, and the genital papillae were classified according to morphological features such as male characteristics (conical protuberances) or female characteristics (flat papillae, sometimes sunk below the body surface). Subsequently, the reliability of the method was verified through gamete observation. Regardless of the season, the methodology resulted in reliable results for approximately 95% of fully mature individuals, while it was somewhat less reliable (approximately 73% accuracy) in nonfully sexually mature sea urchins. The observation of genital papillae morphology is thus a noninvasive, nonlethal (100% survival of animals), that is seasonally independent and inexpensive, and allows the number of animals used during experiments to be minimized, thus promoting animal welfare. This meth-odology is therefore expected to allow gender identification to be conducted year-round, with significant positive impacts in research and actual aquaculture operations.