ヨシエビの生活史初期個体に対する貧酸素および硫化水素曝露の影響

抄録

We examined the tolerance of greasyback shrimp Metapenaeus ensis to hypoxia and H₂S exposure under controlled laboratory conditions. Larvae and juveniles were exposed to normoxic or to hypoxic water (dissolved oxygen concentration <0.5 mg/L) with or without un-ionized H₂S (concentrations, 0.09 to 0.62 mg/L). One-hour exposure experiments revealed ontogenetic changes in the shrimp’s tolerance to hypoxia and H₂S exposure: tolerance to hypoxia was high in larvae at nauplius (survival rate, 100%) and protozoea stages (79%), but was attenuated significantly in larvae at mysis and postlarval stages as well as in juvenile stage (0% for these stages). Presence of H₂S of the concentration >0.1 mg/L enhanced decrease in the survivability after the one-hour exposure even in the hypoxic-tolerant nauplius and protozoea stages. Larvae and juveniles ceased swimming behavior and sank to the bottom soon after the initiation of exposure to hypoxic water with H₂S, followed by death within 24 hours. These results suggest that mass mortality of larvae and juveniles of greasyback shrimp could occur by exposure to hypoxia and H₂S in the field.