The effect of size and diet on gonad production by the Chilean sea urchin Loxechinus albus

Gonadal production was studied in Loxechinus albus (Molina, 1782) maintaine d in cages suspended from a long-line in the Estero Castro, Chiloe for 3 mo during the austral summer. The sea urchins were fed either an artificial d iet or a natural diet consisting of the macroalgae Macrocystis pyrifera and Ulva sp. Both diets were tested for four size ranges: 40-45, 50-55, 60-65 and 70-75 mm diameter. For all four size ranges, highest gonad production w as with the artificial diet. Gonad production was greatest in the 40-45 mm individuals with an increase of about 1,400% and 750% in the wet weight of gonads in individuals fed the artificial and natural diet, respectively. Wi th the three other size ranges, the increase was nearly 100% with the artif icial diet and nearly 0% with the natural diet The gonad index showed simil ar patterns, being highest in the smallest individuals. Small individuals f ed the artificial diet would provide the most cost effective aquaculture as production is best. It is not necessary to grow L. albus to the minimal le gal size for fisheries (70-mm diameter) for cost effective gonad production .