Sex differences in the growth of sea cucumber (Apostichopus japonicus)

Sea cucumber (Apostichopus japonicus) is a commercially important mariculture species in China. Generally, sea cucumbers weighing around 100 g and older than two years, with mature gonads are harvested for food. Sexual dimorphism is widely observed in aquaculture animals, and sex control biotechnologies have created typical cases of genetic breeding in several aquaculture species. Clarifying the sex differences in important economic traits and developing a rapid genetic sex identification method are critical steps for establishing a monosex aquaculture population. In the present study, we established a loop-mediated isothermal amplification (LAMP) based method to identify the genetic sex of sea cucumbers in the field without complex equipment. Subsequently, we investigated the growth difference between males and females in terms of weight gain, and revealed that there was no significant growth difference between males and females 1-2 -year -old juvenile sea cucumbers with undifferentiated gonads. However, among 2-3 -year -old adult sea cucumbers with differentiated gonads, males exhibited greater growth advantages compared to females. The weight increment and specific growth rate (SGR) of male sea cucumbers were 1.73 and 1.52 times greater than those of female sea cucumbers, respectively, highlighting the economic value in producing all -male populations of A. japonicus. Furthermore, the expression levels of growth trait candidate genes (hgfr1 and c-myc) in the body wall tissues showed no significant differences between males and females of 1-2 -year -old A. japonicus. However, in 2-3 -year -old A. japonicus, the expression levels of these genes were significantly higher in males than in females. Conversely, cyp1a1 and cyp17a genes were more highly expressed in differentiated ovaries than in differentiated testes. This study provides a solid foundation for achieving sex control breeding in sea cucumbers.