Survivorship and growth rates of hatchery-reared sea urchins.

The survivorship and growth rates of juvenile, hatchery reared Psammechinus miliaris (Gmelin) were observed for sea urchins fed different diets, and maintained at varying stocking densities and locations (tank or sea-based). In addition survivorship and growth of second generation hatchery stock was also recorded. Somatic growth rates of juvenile urchins (initial test diameter 6.5 mm SD 1.26) were measured over 9 months. A high lipid, high protein diet supported higher somatic growth of urchins in this size range. Higher stocking densities (4 individuals l(-1) as opposed to 2 individuals l(-1)) adversely affected growth as did location (sea-based urchins being smaller than tank based) although survivorship in all treatments and in both first and second generations was exceptionally high. Further research is required to design diets promoting somatic rather than gonadal growth in urchins below market size.