Acute toxicity of nitrite on tilapia (Oreochromis niloticus) at different external chloride concentrations |
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Authors: | Wang Yanbo Zhang Wenju Li Weifen Xu Zirong |
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Institution: | (1) Animal Science College of Zhejiang University, Hangzhou, China;(2) Food Quality & Safety Department of Zhejiang University, Hangzhou, China |
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Abstract: | Tilapias (Oreochromis niloticus) juveniles (total length 4.9 ± 0.2 cm and weight 1.8 ± 0.2 g) were exposed to several nitrite concentrations (0, 10, 18,
32, 56 and 100 mg l−1) for 96 h, using a semi-static renewal method at chloride levels of 35.0 and 70.0 mg l−1. At the end of the 96-h period, the median lethal concentration (LC50) of nitrite was 28.18 mg l−1 in water with low chloride content (35.0 mg l−1) and 44.67 mg l−1 with high chloride content (70.0 mg l−1, respectively). It indicated that high concentrations of chloride ions could reduce the toxicity of nitrite. During the toxicity
experiments, the behaviour and clinical signs of tilapias were also observed. Furthermore, the test of toxic mechanism was
designed taking five test concentrations, viz., 5, 10, 15 and 20 mg l−1 and a nitrite-free control. Nitrite exposure produced high levels of methaemoglobin (MHb) but did not seem to cause mortality,
as surviving tilapias showed high levels (85.37 ± 2.23 and 53.82 ± 3.44 at 35.0 and 70.0 mg l−1 chloride, respectively). The percentage of MHb exposed to nitrite was significantly higher (P<0.05) than the control (0 mg l−1 nitrite) and increased with the increasing nitrite concentration. However, the percentage of MHb decreased with the increasing
chloride concentration. |
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Keywords: | chloride nitrite Oreochromis niloticus tilapia toxicity |
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