Abstract:

Metapenaeus ensis larvae at various stages were exposed by static renewal method to different concentrations of ammonia (NH_³ + NH_⁴+) in seawater at 33 ppt, pH 8.10 and temperature 30ºC. The 24-hour median lethal concentration (LC_⁵⁰) values were 10.33, 4.82, 35.97, 30.33 and 24.39 mg•l_^-1 ammonia-N (un-ionized plus ionized ammonia as nitrogen); and 0.65, 0.30, 2.25, 1.90 and 1.53 mg•l_^-1 NH_³-N (un-ionized ammonia as nitrogen) for nauplius third substage (N3), zoea second substage (Z2), mysis second substage (M2), postlarvae first and tenth substage (PL1, PL10). The 48-hour LC_⁵⁰ mg•l-1 NH_³-N. The threshold time was 108 hours and the incipient LC_⁵⁰ was 3.04 mg•l_^-1 ammonia-N and 0.22 mg•l_^-1 NH_³-N for PL1. The LC_⁵⁰ values of ammonia-N and NH_³-N decreased with longer exposure. Among the development stages of M. ensis larvae tested, zoea larvae were the least tolerant and mysis larvae the most tolerant to ammonia. The concentrations less than 0.30 mg•l_^-1 ammonia-N and 0.02 mg•l_^-1 NH_³-N are considered safe for rearing M. ensis in the hatchery.

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Date 1991/03/01

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