Influence of gametal release method and larval initial density in the culture of the sea urchin Paracentrotus lividus

The gonads of sea urchins have increased interest for human consumption, as a culinary delicacy worldwide. In Europe, the species Paracentrotus lividus was identified as an ideal candidate to meet the growing demand for this product, due to its high gonadosomatic index and easy access. However, the current commercial model, based on the exploitation its natural populations, may be unsustainable. Therefore, its production in aquaculture would be beneficial to avoid depletion of natural stocks of these organisms. The present study sought to develop a culture system for Paracentrotus lividus in aquaculture, which would allow maintaining the early embryonic and larval stages of this animal. A trial was set using 3 gametal release methods (due to stress induced by capture and by injecting 0.125M and 0.250M of potassium chloride) and 3 densities of sea urchin embryos (530 embryos/L, 1000 embryos/L and 2000 embryos/L), using 5 replicate individual culture tanks for each combined factor. The embryos were obtained by adding gametes to sea water, in a proportion 1 egg : 100 spermatozoids, and by discarding unfertilized floating eggs by decantation. Afterwards, the embryos were transferred to a culture system composed by cylindrical-conical plastic tanks of 2L. These were decontaminated and filled with 0.750L of sea water, continuously aerated through a sterile pipette of 3mL. These tanks were placed on metal shelves, artificially illuminated with daylight fluorescent lamps (18w/765, 400Lux) and maintained at 22°C. The larvae were fed each 2 days, with a mixture of microalgae Tetraselmis chuii, Phaeodactylum tricornumtum and Thalassiosira weliflogii at a concentration of 800-1000 microalgae/mL, adding 15µL, 50µL and 30µL to each individual tank, respectively for each of the initial larval densities introduced. There was an influence of the factor initial larval density in the mortality rate, wherein the number of larvae that died during the trial was much greater, the greater the initial density. There was also an influence of the factor induction of gametes release. The larvae obtained by the injection method with 0.125M KCl recorded a number of dead larvae slightly lower during the trial than the other methods. These results influenced the larval densities at the end of the trial. The factor initial larval density presented no influence, but the induction of gametal release did. At the end of the trial, the larval densities achieved through the injection method with 0.125M KCl were higher than those of other methods. Still, the densities of larvae that survived the trial were very low, under 16 larvae/L. During the 4 weeks trial, the larvae reached the post pluteus stage with 8 tri-radial spicules.