Workpackage 6: Sexual reproduction to provide resting eggs of selected clones will be optimised as these eggs can be used as a cysts bank to increase the genotypic diversity in commercial hatcheries.

For the mass production of rotifers, the amictic way of reproduction is preferred, since it is the fastest and cheapest way to obtain and maintain high-density mass cultures. Sexual reproduction, however is a way to preserve heterogeneity in the gene pool of rotifer populations ( Gómez and Carvalho, 2000; Hagiwara, 1994; Ricci, 2001; Ortells et al., 2000). Resting eggs can be stored and have a long shelf-life, making it a very convenient product to start-up new rotifer cultures. Moreover, they are very tolerant to disinfection procedures and therefore enable the start of bacteria-free and pathogen-free rotifer cultures ( Balompapueng et al., 1997; Dhert et al., 1995). These traits underline the interesting potential of the use of rotifer cysts in aquaculture. In the framework of this study proposal, the advantage of resting eggs resides in the fact that hatcheries could maintain the genetic pool of rotifers strains with exceptional characteristics by frequent inoculation of new cultures at regular time intervals (5).