Abstract
This study was conducted to determine the individual and combined effects of ammonia and nitrite on Litopenaeus vannamei postlarvae (25- to 45-d old PL) at 10 ppt salinity, 28 C, and a pH of 7.8. The independent variables were salinity, total ammonia nitrogen (TAN), and nitrite nitrogen (NO2-N). The TAN experiments were conducted at 18 and 10 ppt salinity, and the NO2-N test was conducted at 10 ppt salinity. Combined TAN and NO2 tests were also conducted at 10 ppt salinity. The 48-h lethal concentration (LC50) values for TAN at 18 ppt salinity, TAN at 10 ppt salinity, and NO2-N at 10 ppt were observed to be 42.92, 39.72 (2.26 and 2.09 mg/L unionized ammonia-N), and 153.75 mg/L, respectively. When NO2-N was adjusted to the lowest observed effect concentration (LOEC) level and TAN concentrations were varied, synergistic effects were observed, with a 48-h LC50 calculated to be 28.2 mg/L TAN (1.49 mg/L unionized ammonia-N). However, when the ammonia level was adjusted to the LOEC and nitrite was varied, antagonistic effects were observed with a 48-h LC50 calculated to be 163.3 mg/L NO2-N. This study demonstrated that the combined toxic effects of ammonia and nitrite need to be considered when developing standard operating procedures for shrimp culture.
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