Use of maize as a food source for sea urchins in a recirculating rearing system

Six diets were tested on the somatic growth and mortality of the sea urchin Paracentrotus lividus reared in a semi-closed system. Three of the diets were algal-based (Palmaria palmata, Laminaria digitata and a mix of L. digitata (80%) plus P. palmata (20%)), the other three being based on maize (pure maize or a mix of maize (80%) plus P. palmata (20%) and maize (80%) plus L. digitata (20%)). Best growth rates were obtained with the mix maize plus P. palmata, the lowest conversion rates were obtained with the algal-based diets. Mortality rates were not significantly different between the diets. Sea urchins (3791) were reared in a semi-closed circuit and fed a mix of maize plus P. palmata. Growth, size distribution and mortality were studied to an age of 23 months, when their mean diameter was 21.4 mm (size distribution from 6 to 46 mm). The fastest growing urchins reached 40 mm in 15 months. Size frequency histograms were extrapolated to show that 25% of the urchin population reach a size >40 mm in 41 months. Forty-nine months would be necessary for 50% of the population to reach that size and 63 months for 75% of the population. © Rapid Science Ltd. 1998