Assessment of magnesium chloride as an anaesthetic for adult sea urchins (Paracentrotus lividus):: incidence on mortality and spawning

During this study different concentrations of magnesium chloride (MgCl2) were tested on adult wild-caught sea urchins (Paracentrotus lividus) immediately after their collection in the field in order to assess whether MgCl2 can act as an anaesthetic during their transport and prevent unplanned spawning. Such accidental spawning is a stress response associated with transport of this species. The mortality and gonadal indices were recorded after a 1-h submersion in different strength solutions of MgCl2 (5, 20, 40, 80 and 100 mmol L-1 MgCl2), followed by 5 h of dry transport under two different temperatures (19 and 25 degrees C). The effective concentration of MgCl2 was defined as one that does not induce mortality and gonad mass loss following sea urchin transport and laboratory conditioning. Treatment of sea urchins with 5 mmol L-1 MgCl2 prevented mortality and unplanned spawning; however, elevated concentrations of magnesium (40, 80 and 100 mM) were toxic to sea urchins, inducing a massive mortality and gonad mass decrease during the acclimatization period, essentially when sea urchins were transported under an elevated temperature (25 degrees C). It is concluded that MgCl2 is a suitable non-toxic anaesthetic, easily available for adult sea urchins (P. lividus) when it is used at its optimal anaesthetizing concentration.