Effect of water pH on the survival rate of larvae of the American tadpole shrimp, Triops longicaudatus (LeConte) (Notostraca: Triopsidae)

Survivorship of the larvae of American tadpole shrimp, Triops longicaudatus, was examined in the paddy water of organic farming soil which was adjusted to different pH values by NaOH solution. Among the range of pH 4.4 to 5.3, all inoculated larvae died within 12 h. In the range of pH 5.9 to 6.6, the survival rate of the larvae until 24 h was more than 50% and the rate increased with increasing pH. The effect of rectifying the acidity of organic farming paddy soil by adding Ca(OH)(2) was examined in artificial paddy containers. The water pH without Ca(OH)(2) was 4.9 during the first 10 days, and all larvae died within 6 days after inoculation. About 60% of larvae survived until 22 days after inoculation in paddy water adjusted to over pH 6.7 by adding Ca(OH)(2). The brooding individuals appeared from 14 days after inoculation and ovipositing behavior was frequently observed. It was determined that the boundary of suitable and unsuitable water pH for larval survival was between 5.7 and 5.9, and the larvae can grow to the ovipositional stage by rectification of soil acidity.